Yearly variation and annual cycle of total column ozone over
Transcript Of Yearly variation and annual cycle of total column ozone over
Yearly variation and annual cycle of total column ozone over New Delhi (29◦N, 77◦E), India and Halley Bay (76◦S, 27◦W), British Antarctic Survey Station and its effect on night airglow intensity of OH(8, 3) for the period 1979–2005
P K JANA1,∗, D K SAHA2 and D SARKAR3
1Department of Chemistry, Institute of Education (P. G) for Women, Chandernagore, Hooghly 712 138, West Bengal, India.
2Department of Chemistry, Dinabandhu Mahavidyalaya, Bangaon, North 24 Parganas 743 235, West Bengal, India.
3Department of Chemistry, Howrah Zilla School, Howrah 711 101, West Bengal, India. ∗Corresponding author. e-mail: [email protected]
A critical analysis made on the long-term monthly, seasonal, yearly variation and annual cycle of total column ozone (TCO) concentration at New Delhi (29◦N, 77◦E), India and Halley Bay (76◦S, 27◦W), a British Antarctic Service Station reveals more decline in yearly mean ozone concentration at Halley Bay than at New Delhi from 1979 to 2005. The nature of variations of monthly mean TCO during the months of August and September was the most identical with that of yearly mean ozone values at New Delhi and Halley Bay, respectively, for the same period. Annual cycles of TCO over these stations are completely different for the above period. The effect of O3 depletion on night airglow emission of OH(8, 3) line at New Delhi and Halley Bay has been studied. Calculations based on chemical kinetics show that the airglow intensity of OH(8, 3) has also been affected due to the depletion of O3 concentration. The yearly variations and annual cycle of intensities of OH(8, 3) line for the above two stations are depicted and compared. It has been shown that the rate of decrease of intensity of OH(8, 3) line was comparatively more at Halley Bay due to dramatic decrease of Antarctic O3 concentration.
1. Introduction
In the upper atmosphere, where the densities of air molecules are relatively small and more high energy photons are sufficient to produce excited species, many constituents fluoresce or chemiluminescence. This self-luminescence of the upper atmosphere called the airglow emission (Midya and Midya 1993) that occurs in all latitude (deMesnes et al. 2011) comprises the light
of the wavelengths ranging from the far UV to near IR (Hargreaves 1992; Gombosi 2004). The airglow emissions do exist during both the day and night including twilight also. The mechanism for excitation involves photo-ionization, photoelectron excitation and chemical excitation. Photoionization, photoelectron excitation and chemical excitation are active during daytime, while the chemical excitation is the only source for the night-time airglow emission apart from the small
Keywords. Ozone depletion; airglow emission; excitation mechanism; intensity.
J. Earth Syst. Sci. 121, No. 6, December 2012, pp. 1527–1541 c Indian Academy of Sciences
1527
1528
P K Jana et al.
contribution from cosmic rays. The lifetime of the excited species ranges from milliseconds to minutes depending upon the altitudes from which they emanate. Green and red lines of oxygen, yellow lines of sodium and OH bands are the main emissions during day, twilight and night time. Meinel (1950a) first identified rotational–vibrational band of OH airglow emission. Meinel (1950a, 1950b, 1950c) discovered various vibration– rotation bands of the OH radical in the night airglow. These are known as the Meinel (M) bands, viz., OH M(7, 4) band, OH M(6, 3) band, OH M(3, 1) band, OH M(4, 2) and OH(5, 3) R heads. OH M(7, 4) band, OH M(6, 3) band, OH M(3, 1) band, OH M(4, 2) band and OH M(5, 3) band have been identified near 7530, 8744, 6169, 6503, and 6165 cm−1, respectively. OH(8, 3) is the other important emission of airglow spectrum. Takahashi et al. (1974) identified OH(8, 3) band airglow emission at latitude of 23◦S. They also reported that nocturnal variation of intensity was correlated with that of a rotational temperature. Krassovsky and Shagaev (1974) observed the wave-like propagation of disturbances of rotational temperature of OH(8, 3). Takahashi et al. (1977) studied the diurnal and seasonal variation of intensity of OH(8, 3) emission from 1972 to 1974. It showed a significant seasonal effect. The OH(8, 3) emission was found to increase slightly during magnetic disturbances. The proposed excitation mechanism (Bates and Nicolet 1950) of OH(8, 3) line indicates that the intensity of OH(8, 3) line is affected with the variation of ozone concentration.
Ozone, though a very minor atmospheric constituent, plays an important role to control the chemical kinetics of troposphere, stratosphere and mesosphere. The global ozone assessment confirms that ozone is declining everywhere in smaller amount (Bojkov 1992). But Farman et al. (1985) first reported that dramatic decrease of ozone concentration takes place at Antarctica during spring time causing an ozone hole. Afterwards, it was verified by different investigators all over the world (Midya and Jana 2002).
Conventionally, it is assumed that there is an ozone hole when the ozone abundance is ≤220 Dobson units (D U) (1 DU = 0.001 atm cm) in a specific geographic place (WMO 2002). The 1997 monthly averaged column ozone from the total ozone mapping spectrometer (TOMS) is up to 25 DU lower than the TOMS climatological mean (1979–1996) and up to 20 DU below the previous record low values (Cordero and Nathan 2002). Kerr (1998) reported that the 1998 Antarctic ozone hole is the biggest one ever observed. Average area of ozone hole was 25.3 × 106 km2 in September and 20.6 × 106 km2 in October 1998. The area of Antarctic ozone hole (area of O3 < 220 DU)
increased (Uchino et al. 1999) steadily from 1979 to 1998 and the 2000 ozone hole was the largest on record (Bodeker et al. 2002). Averaged area of the Antarctic ozone hole, determined by the area enclosed by the 220 DU total ozone contour, increased (Madrigal and Peraza 2005) from 2.6 × 106 to 25.8 × 106 km2 for the month of September and from 2.7 × 106 to 16.7 × 106 km2 for the month of October, during 1982–2003. Several theories have been proposed for the Antarctic ozone hole. Chemical, dynamical and natural theories are mainly important and are explained in an earlier publication (Jana and Nandi 2005). If ozone hole is created at any place in the atmosphere, O3 concentration also decreases in other regions due to atmospheric diffusion and circulation (Jana and Nandi 2005).
Measurement of airglow emission can be used as an important tool in studying the behaviour of the ionosphere and the upper atmosphere basically on the dynamical–photochemical processes that control the species composition and energy balance (Krasnopolsky 1986; Haider et al. 1992; Slanger et al. 2001). OH airglow emissions can be used as tracers of gravity wave (GW) that play an essential role in determining the global circulation and thermal balance of the atmosphere. A realistic GW parameterization is important for accurate atmospheric model. Dynamic control of OH altitude/ temperature at high latitudes was supported by the anti-correlation between OH peak altitude and temperature found in SABER (Sounding of the Atmosphere using Broadband Emission Radiometry) data (Winick et al. 2009) and also between OH peak altitude and meridional wind strength (Dyrland et al. 2010). Measurement of OH airglow can be used to derive atomic hydrogen concentration if ozone density is known (Mlynczak et al. 1998) and the OH rotational temperature near the mesopause (Lowe and Turnbull 1995). The OH airglow emission can extensively be used for studying atmospheric temperature variation at mesospheric region (Greet et al. 1998; Bittner et al. 2000). The airglow OH(8-3) and (6-2) band rotational temperatures were measured and compared using two scanning photometer at Cachoeira Paulista (23◦S, 45◦W) in 1999. The rotational temperature were obtained from the ratio between the P1(5) and P1(3) in the case of (8-3) band and P1(4) and P1(2) lines for the (6-2) band. It was shown that both the temperature did agree well (Wrasse et al. 2004).
Airglow emission can be influenced by atmospheric parameters including temperature, vertical advection, diffusion and some chemical species. Moreover, its temporal and spatial distributions are often modulated by dynamical perturbation such as gravity waves, planetary waves, tides and
Yearly variation and annual cycle of TCO over New Delhi and Halley Bay
1529
so on. Stratospheric sudden warming (SSW), the most important event in the mid-winter polar stratosphere can perturb atmospheric temperature, winds and distribution of several atmospheric chemical constituents in the middle atmosphere (Sathiskumar and Sridharan 2009; Funke et al. 2010). Therefore, influence of variation of total column ozone on OH airglow emission is an important approach for investigating the coupling between stratosphere and mesosphere-lower thermosphere (MLT) region (Gao et al. 2011). Wiens and Weill (1973) on analysis of the diurnal, annual and solar cycle variations in OH nightglow reported that the diurnal variation patterns altered with latitude and season and OH nightglow intensity followed the solar activity. Batista et al. (1994) showed that the OH(9, 4) band intensity had a positive correlation with the F 10.7 index. Abreu and Yee (1989) on the basis of the seasonal variations in the OH(8, 3) nightglow emission pointed out that there was a strong semi-annual oscillation with maxima near the equinoxes in the OH nightglow. Marsh et al. (2006) mentioned that the OH nightglow was stronger than the OH day glow. Shephered et al. (2006) showed that a 1% increase in temperature led about 4% increase in OH emission and OH emission was linearly sensitive to atomic oxygen concentration on the bottom side of the atomic oxygen layer.
In this paper, the nature of variations of monthly, yearly and seasonal total column ozone (TCO) over New Delhi and Halley Bay has been presented from 1979 to 2005. The most and the least identical monthly and seasonal variations with that of yearly TCO have been identified for these stations. Annual cycle of monthly TCO over these two stations has also been depicted. From the excitation mechanism OH(8, 3) airglow emission, the volume emission rate for different altitudes are computed. From the volume emission rate curve, the intensity of OH(8, 3) has been calculated for the year 1979. Following this process, the intensity of the same line over two stations, namely, New Delhi, India which has comparatively less depletion in ozone concentration and Halley Bay (76◦S, 27◦W), a British Antarctic Survey station which has comparatively much more depletion in ozone concentration, have been calculated for other years, considering the fluctuation percentages of O3 concentrations assuming that the variation of OH intensity is unaffected by the density of atomic hydrogen. The nature of different type of variations of TCO and intensities of OH(8, 3) is compared over these two stations because the stations are associated with distinctly different rates of ozone depletion without considering the semiannual oscillation (SAO), annual oscillation (AO) and quasi-biennial oscillation (QBO). In our previous
publications (Jana and Nandi 2006; Jana et al. 2011), effect of long term TCO on intensities of Na 5893 ˚A nightglow line and lithium 6708 ˚A over Dumdum (22.5◦N, 88.5◦E) and Varanasi (25◦N, 83◦E) had been presented and compared with that at Halley Bay (76◦S, 27◦W), respectively which showed same type of excitation mechanisms of sodium and lithium airglow emissions having different types of their importance in mesosphere. In case of OH(8, 3) airglow emission, the excitation mechanism and the role of OH(8, 3) which is stated above are completely different from the sodium and lithium airglow emission.
2. Data and analysis
Total column ozone densities of different stations have been obtained from the website http://jwocky. gsfc.nasa.gov (Jana et al. 2010a, 2010b). Monthly mean ozone densities have been calculated from daily average value of ozone in DU for the stations, namely, New Delhi and Halley Bay. The yearly mean ozone densities have been calculated from monthly average value of ozone in DU. The mean ozone for December, January and February (DJF) provides winter (summer) ozone, March, April and May (MAM) constitute pre-monsoon (fall) values, June, July and August (JJA) make monsoon (winter) values and September, October and November (SON) comprise post-monsoon (spring) values for the station New Delhi (Halley Bay), respectively. Total ozone data has been measured by the satellites Nimbus-7 Total Ozone Mapping Spectrometer (TOMS), Earth probe TOMS and Ozone Monitoring Instrument (OMI). TOMS and OMI provide high resolution daily global information about the total ozone content of the atmosphere by measuring ultraviolet sunlight backscattered from the ground. TCO in this study includes retrievals from Nimbus 7 (November 1978 to May 1993) and Earth probe (July 1996 to present) total ozone mapping spectrometer (TOMS). Data from HALOE (halogen occultation experiment) are used in this first method to extend the vertical span of MLS (highest pressure level 46 hPa) using simple regression. This assimilation enables high resolution daily maps of tropospheric and stratospheric ozone which is not possible from solar occultation measurements alone, such as from HALOE or Stratospheric Aerosols and Gas Experiment (SAGE) (Jana et al. 2012).
3. Results and discussions
The proposed excitation mechanisms of OH(8, 3) band are as follows:
1530
P K Jana et al.
1. Bates–Nicolet mechanism (Bates and Nicolet 1950)
O + O2 + M →K1 O3 + M,
(1)
O3 + H →K2 O2 + OH∗ (3.32 ev) ,
(2)
OH∗ A→vv OH + hv,
(3)
where K1 = 1.5×10−34 exp (445/T) cm√6 S−1 (Stuhl and Niki 1971) and K2 = 1.5 × 10−12 T cm3 S−1 (Nicolet 1970).
2. Breig mechanism (Breig 1970)
H + M + O2 →K3 HO2 + M,
(4)
HO2 + O →K4 OH∗ + O2,
(5)
where K3 = 3.3 × 10−33 exp(800/T√) cm6 S−1 (Gattinger 1971) and K4 = 1.5 × 10−12 T cm3 S−1 (Gattinger 1971).
3. Krassovsky mechanism (Krassovsky 1956)
O2 + O + M →K5 O3 + M,
(6)
O + O3 →K6 O∗2 + O∗2,
(7)
O∗2 + H →K7 OH∗ + O,
(8)
where K5 = 1.5×10−32 cm6 S−1 (Midya et al. 1998) and K7 = 10 × 10−10 cm3 S−1 (Midya et al. 1998). K1, K2, K3, K4, K5, K6 and K7 are all reaction rate constants. Midya et al. (1998) have established that Bates–Nicolet mechanism is the predominant and appropriate excitation mechanism of OH emission.
According to Bates–Nicolet mechanism, ignoring quenching terms, the volume emission rate of OH* is given by:
n (OH∗) = K2 [O3] [H]
(9)
So, the volume emission rate of OH(8, 3) band will be as follows:
Q∗OH = A8,3K2 [O3] [H] / Avv . (10)
where Avv is the Einstein transition probability from vibrational level v to v .
A8,3 = 0.0296 S−1
(11)
Avv = 13.5 (Midya et al. 1998). (12)
The Einstein A-coefficients associated with the OH* vibrational emissions have been measured in the laboratory (Nelson et al. 1990). Uncertainties regarding the quenching lifetimes and the rate constants for the reactions with atomic O remain fairly large (Mlynczak et al. 1998) and make the interpretation of the airglow feature difficult (Llewellyn et al. 1978).
Using the number densities of O3 and H, the volume emission rates of OH(8, 3) band for different altitudes have been calculated with the help of the equation (10). It attains maximum value at an altitude of 80 km. Altitudinal number densities of O3 and H and volume emission rates of OH(8, 3) band have been shown in table 1. Intensity has then been calculated from the volume emission rate curve with the help of the following equation:
Intensity = 1 × layer thickness 2 × peak volume emission rate. (13)
The value of layer thickness was 14.8 km and peak volume emission rate was 46 × 102 cm−3 s−1 for normal volume emission rate curve shown in figure 1. Thus, the intensity of OH(8, 3) band became 34.04 KR (KiloRayleigh) (1R = 1.0 × 105 cm−2 s−1). The number densities of H and O3 have been taken from Jacchia (1977). The OGOsatellite mass spectrometer launched in 1969 provided the first measurements of the densities of N2, O and He in the thermosphere. The observed variations in composition did not agree with Jacchia model. Accuracy may be improved with the corresponding data produced from MSIS (Mass Spectrometer and incoherent Scatter) model for various geographical, temporal and solar conditions, but pattern of variations of yearly, seasonal and annual cycle of OH intensities would be unaltered. The latest model, MSIS-86 was chosen for CIRA (COASPER International Reference) 1986. The database for MSIS-86 consists of composition, temperature and density data with in situ thermospheric measurements as well as rockets and ground based scatter stations (Marcos 1987). Gao et al. (2010) had also calculated the mean OH nightglow emission rate at the altitude of 88 km, the temperature and [O3] at 88 km which were observed by SABER, but they did not use [O] and [H] data measured by SABER because of large errors. They found that the distribution of the OH nightglow emission rate at 88 km, the peak emission rate (Vmax), intensity (I) and [O3] are similar to one another. Thus, they also concluded that the seasonal variations of temperature, [O], and [O3] played an important role in the seasonal variation of OH nightglow emission, Vmax and I. The TIMED (Thermosphere, Ionosphere, Mesosphere, Energetics, and Dynamics) satellite was launched on 7 December. The height of the TIMED circular orbit is about 625 km and the inclination is 74.1◦. The SABER, one of the four instruments onboard the TIMED satellite directly measures atmospheric emissions, such as OH airglow emission, O2 airglow emission and NO airglow emission over a broad spectral range using a multichannel infrared
Yearly variation and annual cycle of TCO over New Delhi and Halley Bay
1531
8.52 30.79 48.41 59.34 65.92 62.98 56.4 49.59 46.06 40.65 36.07 31.49 27.73 22.68 18.09 13.28
Halley Bay cm−3 s−1× 10−2
11.75
16.02
20.07
25.45
27.87
31.93
35.98
40.77
43.89
49.92
57.74
58.34
52.52
42.85
27.25
7.54
New Delhi cm−3 s−1× 10−2
Volume emission rates(Q) of OH(8, 3)
11.3
15.4
19.3
23.6
26.8
30.7
34.6
39.2
42.2
48
53.6
56.1
50.5
41.2
26.2
7.25
Normal cm−3 s−1
n(O3) × 10−8 Halley Bay 3.76 3.29 2.94 2.47 2.12 1.65 1.53 1.41 1.36 1.27 1.18 1.2 1.22 1.25 1.27 1.29
1.14
1.12
1.1
1.08
1.06
1.04
1.12
1.21
1.25
1.35
1.46
1.87
2.18
2.6
2.91
3.33
n(O3) × 10−8 New Delhi
Number densities (atoms/cc)
radiometer and indirectly measures atmospheric parameters, such as temperature, atmospheric density, ozone density, atomic oxygen density and so on.
Variations of yearly mean ozone concentrations at New Delhi and Halley Bay have been presented in figures 2 and 3, respectively, from 1979 to 2005. The nature of variations of ozone concentrations for each month for different years has been compared with the variation of yearly mean ozone concentrations. It has been observed that the variations of ozone concentrations for all months and variation of yearly mean ozone values followed nearly the same trend. The nature of variation of mean ozone values during the month of August from 1979 to 2005 was the most identical with the variation of yearly mean ozone values for the same period and the variation of mean ozone values during the month of December was the least identical with the variation of yearly mean ozone values for the same period at New Delhi. It has also been verified by the value of coefficient of correlation as depicted in figure 4 that depicts the variation of correlation coefficients with months at New Delhi (29◦N, 77◦E) and at Halley Bay (76◦S, 27◦W) from 1979 to 2005. The coefficient of correlation between August ozone mean values with yearly mean values was the maximum (0.82). It was the minimum for December ozone mean values (0.35). The yearly mean ozone concentration as well as the concentrations of ozone for every month was gradually decreasing from 1979 to 2005 at different rates at New Delhi. The rate of yearly mean ozone depletion was 0.3629 DU per year. It was 0.2102 and 0.8053 DU per year for the months of August and December, respectively. Therefore, the variation of August concentration of ozone mostly controlled the variation of annual TCO over New Delhi from 1979 to 2005 as the rate of ozone fall in August from 1979 to 2005 was the closest to that of annual TCO.
But in case of Halley Bay, the nature of variation of mean ozone values during the month of September from 1979 to 2005 was the most identical with the variation of yearly mean ozone values for the same period and the variation of mean ozone values during the month of April was the least identical with the variation of yearly mean ozone values for the same period. It has also been verified by the value of coefficient of correlation as shown in figure 4. The coefficient of correlation between September ozone mean values with yearly mean values was the maximum (0.97). It was the minimum for April ozone mean values (0.51). The yearly mean ozone concentration as well as the concentrations of ozone for every month was gradually decreasing from 1979 to 2005 at different rates. The rate of yearly mean ozone
11.3
15.4
19.3
23.6
26.8
30.7
34.6
39.2
42.2
48
53.6
56.1
50.5
41.2
26.2
7.25
QOH(8, 3) × 10−2
n(H) × 10−8 0.51 2.1 3.7 5.4 7 8.6 8.3 7.9 7.6 7.2 6.9 5.9 5.1 4.1 3.2 2.3
n(O3) × 10−8 3.2 2.8 2.5 2.1 1.8 1.4 1.3 1.2 1.16 1.08 1 1.02 1.04 1.06 1.08 1.1
Table 1. Volume emission rates of OH(8, 3).
Altitude (km) 75 76 77 78 79 80 81 82 83 84 85 86 87 88 89 90
1532
P K Jana et al.
92
90
88
Normal
New Delhi
86
Halley Bay
84
Altitude (km)
82
80
78
76
74
0
10
20
30
40
50
60
70
Volume emission rate of OH (8, 3) x 10 -2(cm -3 s-1 )
Figure 1. Altitudinal variations of volume emission rates of OH(8, 3) band at New Delhi (29◦N, 77◦E) and at Halley Bay (76◦S, 27◦W).
depletion was 2.684 DU per year. It was 4.7434 and 1.0914 DU per year for the months of September and April, respectively. So, the variation of yearly mean TCO over Halley Bay was controlled by that of September ozone values.
300
290
280
Seasonal variations of ozone densities at New Delhi reveal the most identical variation in DJF (winter) and least identical variation in SON
350 Apr
Sep
Mean
300
Fall
Spring
Density of ozone (DU) at New Delhi (29oN, 77oE) Density of ozone (DU) at Halley Bay (76 o S, 27o W)
270 250
260
250
240
230
Aug
Dec
220
Mean
Winter
210
Post-monsoon
200 1979 1982 1985 1988 1991 1994 1997 2000 2003 Year
200
150
100 1979 1982 1985 1988 1991 1994 1997 2000 2003 Year
Figure 2. Variation of ozone concentration at New Delhi (29◦N, 77◦E) from 1979 to 2005.
Figure 3. Variation of ozone concentration at Halley Bay (76◦S, 27◦W) from 1979 to 2005.
Coefficient of correlation between monthly mean and yearly mean ozone variation during 1979 to 2005
Ozone density (DU)
Yearly variation and annual cycle of TCO over New Delhi and Halley Bay
1533
1
380
0.9
0.8
330
0.7
0.6
0.5
280
0.4
0.3
0.2 New Delhi Halley Bay
0.1
230
0 Jan Feb Mar Apr May Jun Jul Aug Sep Oct Nov Dec
Months
180
New Delhi Halley Bay
Figure 4. Variation of correlation coefficients with months at New Delhi (29◦N, 77◦E) and at Halley Bay (76◦S, 27◦W) from 1979 to 2005.
(post-monsoon) with yearly mean variation. The rate of ozone depletion was 0.0763 and 0.028 DU per year in winter and post-monsoon, respectively. But, in case of Halley Bay, the most identical seasonal variations of ozone were observed in SON (spring), while the least identical seasonal variation in MAM (fall) with yearly mean ozone variation. The rate of ozone decline was 0.7174 and 0.159 DU per year in spring and fall, respectively.
Annual cycle of ozone concentrations for the stations at New Delhi and Halley Bay for the period 1979–2005 have been shown in figure 5, respectively. At New Delhi, ozone concentration attained the maximum value for the months of June and July. The minimum ozone concentration occurred for the months of December and January. Ozone concentration gradually increased from the month of January, attained its maximum for the period of June and July, then gradually decreased and reached its minimum value for the month of December.
In case of Halley Bay, ozone concentration attained the maximum value for the months of December and January. The minimum ozone concentration occurred at the months of September and October. Maximum ozone concentration occurred during the month of January, then gradually decreased, attained minimum for the month of September–October and then gradually increased. At both the stations, annual cycle of ozone densities for every year and their mean annual cycle followed nearly the identical variations.
Equation (10) clearly reveals that the volume emission rate of OH(8, 3) band is directly proportional to the concentrations of H and ozone
130
JAN
AR M
AY M
JUL SEP
NOV
Months
Figure 5. Annual cycle of ozone concentration at New Delhi (29◦N, 77◦E) and Halley Bay (76◦S, 27◦W).
(O3 + H → OH* + O2) with the reaction rate increasing with increasing temperature. O3 is produced from the reaction O + O2 + M → O3 + M and is destroyed mostly by the reaction O3 + H* → OH* + O2 and O + O3 → O2 + O2. The destruction of ozone due to the reaction with H is larger than the reaction with O by several orders of magnitude below 95 km (Xu et al. 2010). So, the contribution of producing OH airglow is somewhat nullified by the destruction of O3 that produces OH airglow. The production of O3 and consequent OH nightglow emission at mesosphere are proportional to the atomic oxygen density, thus OH airglow emission is influenced by atomic oxygen, ozone densities and also by atmospheric temperature. Ward (1999) reported that the OH nightglow is approximately proportional to the volume mixing ratio of O. Marsh et al. (2006) indicated that the transport of O is responsible for the annual cycle of the SABER OH emissions at higher latitudes. Xu et al. (2010) pointed out that the SABER OH nightglow brightness and temperature near the equator were positively correlated below about 94 km and negatively correlated above. The concentration of ozone in stratosphere varies in considerable amount from year to year, as well as from month to month. This stratospheric variation of ozone may influence the mesospheric altitudinal concentration of ozone. On the basis of recent study on the
Table 2. Yearly variation of intensity of OH(8, 3) at New Delhi and Halley Bay.
Year
Mean O3 (DU) at New Delhi
O3 fluctuation % from mean at New Delhi
Mean O3 (DU) at Halley Bay
O3 fluctuation % from mean at Halley Bay
Peak volume emission
rate OH(8, 3) at
New Delhi cm−3 s−1
1979 1980 1981 1982 1983 1984 1985 1986 1987 1988 1989 1990 1991 1992 1993 1994 1995 1996 1997 1998 1999 2000 2001 2002 2003 2004 2005
287.81 280.13 285.11 289.69 278.07 279.13 267.1 276.24 275.4 270.21 283.35 279.64 283.3 275.74 265.63 277.33 273.8 270.22 275.87 278.16 272.39 276.11 278.42 270.95 277.45 296.7 274.22
4.007 1.225 3.03 4.687 0.487 0.87 −3.476 −0.173 −0.477 −2.428 2.395 1.055 2.348 0.058 −4.911 −0.852 1.005 −2.348 −0.307 0.513 −1.568 −0.22 0.614 −2.085 0.263 −2.54 −0.907
300.54 299.48 294.94 286.14 286.56 271.33 264.93 267.56 258.03 279.77 261.99 251.04 254.01 250.08 251.29 233.57 237.84 242.1 252.6 227.91 228.39 236.13 227.81 253.04 226.09 234.09 227.81
17.5 17.08 15.31 11.87 12.03
6.08 3.37 4.61 0.88 9.38 2.43 −1.85 −0.69 −1.95 −1.76 −8.68 −7.01 −5.35 −1.24 −10.89 −10.71 −7.68 −10.94 −1.07 −11.37 −8.36 −10.94
58.34 56.79 57.79 58.73 56.37 56.59 54.15 56 55.83 54.74 57.45 56.69 57.42 56.13 53.35 55.62 55.53 54.78 55.93 56.39 55.22 55.98 56.45 54.93 56.23 54.68 55.59
Peak volume emission rate OH(8, 3) at Halley Bay cm−3 s−1
65.92 65.68 64.69 62.76 62.85 59.51 57.99 58.69 56.39 61.36 57.46 55.06 55.71 55 55.11 51.23 52.17 53.1 55.4 49.99 50.09 51.79 49.96 55.5 49.72 51.4 49.96
Intensity of OH(8, 3) line at New Delhi KR
35.4 34.46 35.07 35.64 34.21 34.34 32.86 33.98 33.88 33.21 34.86 34.4 34.84 34.06 32.37 33.75 33.7 33.24 33.93 34.21 33.51 33.97 34.25 33.33 34.13 33.18 33.73
Intensity of OH(8, 3) line at Halley Bay KR
39.99 39.85 39.25 38.08 38.14 36.11 35.19 35.61 34.34 37.23 34.87 33.41 33.81 33.38 33.44 31.09 31.65 32.22 33.62 30.33 30.39 31.43 30.32 33.68 30.17 31.19 30.32
P K Jana et al.
1534
Table 3. Seasonal variation of intensity of OH(8, 3) from 1979–2005 at New Delhi.
Yearly variation and annual cycle of TCO over New Delhi and Halley Bay
Year
Amount of O3(DU) in winter
O3 fluctuation
% from mean in winter
Intensity of OH(8, 3) in winter KR
Amount of O3
(DU) in pre-monsoon
O3 fluctuation
% from mean in pre-monsoon
Intensity of OH(8, 3) in pre-monsoon
KR
Amount of O3 (DU) in monsoon
O3 fluctuation
% from mean in monsoon
Intensity of OH(8, 3) in monsoon
KR
Amount of O3
(DU) in post-monsoon
O3 fluctuation
% from mean in post-monsoon
Intensity of OH(8, 3) in post-monsoon
KR
1979 1980 1981 1982 1983 1984 1985 1986 1987 1988 1989 1990 1991 1992 1993 1994 1995 1996 1997 1998 1999 2000 2001 2002 2003 2004 2005
290.33 270.95 284.84 282.59 274.61 285.28 259.69 274.01 263.21 269.61 279.51 277.43 275.78 267.14 256.55 276.54 267.78 259.03 265.15 270.86 263.18 268.55 265.92 258.96 276.65 257.8 263.96
7.29 0.13 5.27 4.43 1.49 5.43 −4.03 1.26 −2.73 −0.36 3.3 3.21 1.92 −1.27 −5.19 5.6 −1.04 −4.27 −2.01 3.39 −2.73 −0.75 −1.72 −2.05 2.24 −4.73 −2.45
36.52 34.08 35.83 35.55 34.55 35.89 32.67 34.47 33.11 33.92 35.16 35.13 34.69 33.61 32.27 35.95 33.69 32.59 33.36 35.19 33.11 33.78 33.45 33.34 34.8 32.43 33.21
299.8 292.46 296.46 310.88 281.68 287.25 269.19 288.13 293.21 272.29 290.6 289.23 297.21 291.94 274.43 287.48 287.33 286.52 285.72 290.17 268.56 289.65 296.57 276.89 288.89 276.8 290.11
4.31 1.76 3.16 8.17 −1.99 −0.05 −6.33 0.26 2.03 −5.24 1.17 0.64 3.42 1.6 −4.51 0.03 −0.02 −0.03 −0.58 0.97 −6.55 0.79 3.19 −3.65 0.52 −3.68 0.95
35.51 34.64 35.12 36.82 33.36 34.02 31.88 34.13 34.73 32.26 34.44 34.25 35.2 34.58 32.5 34.05 34.03 33.94 33.84 34.37 31.81 34.31 35.13 32.79 34.22 32.78 34.36
287.86 284.27 283.2 292.17 282.13 281.9 272.77 274.94 283.94 273.93 286.78 280.32 286.87 280.46 273.77 277.75 276.53 275.32 278.48 283.15 283.75 284.98 284.59 278.68 282.28 280.51 282.49
2.35 1.07 0.69 3.35 0.38 0.23 −3.02 −2.23 0.96 −2.59 1.97 −0.33 1.88 1.34 −2.66 −1.24 −1.68 −2.11 −0.98 0.68 0.89 1.33 1.19 −0.91 0.36 −0.26 0.44
34.84 34.4 34.27 35.24 34.16 34.12 32.95 32.28 34.37 33.16 34.71 33.93 34.68 34.5 33.13 33.62 33.477 33.32 33.71 34.27 34.34 34.49 34.45 33.37 34.16 33.95 34.19
273.24 272.78 275.93 273.11 268.56 262.07 266.74 267.86 261.13 264.99 272.99 271.58 273.33 263.43 257.97 267.55 263.54 260.02 274.13 263.74 274.06 261.25 266.44 269.26 261.99 263.68 260.29
2.3 2.13 3.31 2.25 0.55 −1.88 0.13 0.28 −2.67 0.79 2.21 1.67 2.33 1.37 3.42 0.17 −1.33 −2.65 2.63 −1.26 2.61 −2.19 −0.25 0.81 1.91 −1.28 −2.51
34.82 34.77 35.17 34.8 34.23 33.4 34.08 34.14 33.13 34.31 34.79 34.61 34.83 34.51 35.2 34.1 33.59 33.14 34.93 33.61 34.93 33.29 33.95 34.32 34.69 33.6 33.19
1535
Table 4. Seasonal variation of intensity of OH (8, 3) from 1979–2005 at Halley Bay.
Year
Amount of O3 (DU) in Summer
O3 fluctuation
% from mean in Summer
Intensity of OH(8, 3) in Summer KR
Amount of O3
(DU) in Fall
O3 fluctuation
% from mean in
Fall
Intensity of OH(8, 3) in Fall KR
1979 1980 1981 1982 1983 1984 1985 1986 1987 1988 1989 1990 1991 1992 1993 1994 1995 1996 1997 1998 1999 2000 2001 2002 2003 2004 2005
320.19 332.7 325.95 314.14 326.53 311.3 302.05 298.94 297.21 308.26 299.85 284.85 300.78 295.53 296.48 288.29 288.35 288.41 299.52 253.5 262.71 284.39 273.54 286.13 284.01 278.74 270.89
8.43 12.66 10.37
6.38 10.57
5.41 2.43 1.23 0.64 4.39 1.54 3.54 1.85 0.07 0.4 −2.38 −2.36 −2.34 1.43 −14.16 11.03 3.7 −7.37 −3.11 3.83 −5.61 −8.27
36.88 38.35 37.57 36.21 37.64 35.88 34.87 34.46 34.26 35.53 34.56 35.25 34.67 34.06 34.18 33.23 33.24 33.24 34.53 29.22 37.79 35.19 31.53 32.98 35.34 32.28 31.22
293.79 299.26 279.5 287.37 287.7 278.83 275.28 251.98 280.33 279.08 275.21 269.34 263.16 278.78 277.4 274.28 272.53 270.81 269.05 269.99 263.66 260.69 258.77 256.13 252.16 251.14 252.1
8.24 10.26
2.98 5.88 2.68 2.73 1.42 −7.16 3.28 2.82 1.4 −0.76 −3.04 2.71 2.2 1.05 0.41 −0.22 −0.87 −0.52 −2.86 −3.95 −4.66 −5.6 −7.1 −7.47 −7.12
36.84 37.53 35.05 36.04 34.95 34.97 34.52 31.36 35.16 34.99 34.52 33.78 33.01 34.96 34.79 34.4 34.18 33.97 33.74 33.86 33.07 32.7 32.45 32.14 31.62 31.5 31.62
Amount of O3 (DU) in Winter
289.61 290.15 289.03 289.93 272.82 265.78 259.28 264.22 262.08 268.19 254.2 243.29 238.32 238.9 252.88 205.51 218.87 232.23 251.58 229.3 231.53 221.46 216.99 226.34 198.6 224.36 210.03
O3 fluctuation
% from mean Winter
17.66 17.88 17.43 17.8 10.84
7.98 5.34 7.35 6.48 8.96 3.28 −1.15 −3.17 2.94 2.74 −16.5 −11.08 5.65 2.21 −6.84 −5.93 −10.02 −11.84 8.04 19.31 −8.84 −14.67
Intensity of OH(8, 3) in Winter
KR
40.05 40.13 39.97 40.1 37.73 36.76 35.86 36.54 36.25 37.09 35.16 33.65 32.96 35.04 34.97 28.42 30.27 35.96 34.08 31.71 32.02 30.57 30.01 36.78 40.6 31.03 29.05
Amount of O3
(DU) in Spring
298.58 275.82 285.29 259.11 259.2 229.42 220.94 255.11 192.49 263.53 218.68 206.65 213.78 189.92 178.39 166.21 171.59 176.97 190.04 158.87 155.67 177.97 161.92 243.56 171.98 183.32 178.21
O3 fluctuation
% from mean in Spring
41.95 31.04 35.54 23.1 23.14
8.99 4.96 21.98 8.55 25.2 3.89 −1.82 1.56 −9.77 −15.25 −21.03 18.49 −15.92 −9.72 −24.52 −26.04 −15.45 −23.07 15.71 −18.3 −12.91 −15.34
Intensity of OH(8, 3) in Spring KR
48.32 44.73 46.14 41.9 41.92 37.1 35.73 41.52 36.95 42.62 35.36 33.42 34.57 30.71 28.85 26.88 40.33 28.62 30.73 25.69 25.18 28.78 26.19 39.39 27.81 29.65 28.82
P K Jana et al.
1536
P K JANA1,∗, D K SAHA2 and D SARKAR3
1Department of Chemistry, Institute of Education (P. G) for Women, Chandernagore, Hooghly 712 138, West Bengal, India.
2Department of Chemistry, Dinabandhu Mahavidyalaya, Bangaon, North 24 Parganas 743 235, West Bengal, India.
3Department of Chemistry, Howrah Zilla School, Howrah 711 101, West Bengal, India. ∗Corresponding author. e-mail: [email protected]
A critical analysis made on the long-term monthly, seasonal, yearly variation and annual cycle of total column ozone (TCO) concentration at New Delhi (29◦N, 77◦E), India and Halley Bay (76◦S, 27◦W), a British Antarctic Service Station reveals more decline in yearly mean ozone concentration at Halley Bay than at New Delhi from 1979 to 2005. The nature of variations of monthly mean TCO during the months of August and September was the most identical with that of yearly mean ozone values at New Delhi and Halley Bay, respectively, for the same period. Annual cycles of TCO over these stations are completely different for the above period. The effect of O3 depletion on night airglow emission of OH(8, 3) line at New Delhi and Halley Bay has been studied. Calculations based on chemical kinetics show that the airglow intensity of OH(8, 3) has also been affected due to the depletion of O3 concentration. The yearly variations and annual cycle of intensities of OH(8, 3) line for the above two stations are depicted and compared. It has been shown that the rate of decrease of intensity of OH(8, 3) line was comparatively more at Halley Bay due to dramatic decrease of Antarctic O3 concentration.
1. Introduction
In the upper atmosphere, where the densities of air molecules are relatively small and more high energy photons are sufficient to produce excited species, many constituents fluoresce or chemiluminescence. This self-luminescence of the upper atmosphere called the airglow emission (Midya and Midya 1993) that occurs in all latitude (deMesnes et al. 2011) comprises the light
of the wavelengths ranging from the far UV to near IR (Hargreaves 1992; Gombosi 2004). The airglow emissions do exist during both the day and night including twilight also. The mechanism for excitation involves photo-ionization, photoelectron excitation and chemical excitation. Photoionization, photoelectron excitation and chemical excitation are active during daytime, while the chemical excitation is the only source for the night-time airglow emission apart from the small
Keywords. Ozone depletion; airglow emission; excitation mechanism; intensity.
J. Earth Syst. Sci. 121, No. 6, December 2012, pp. 1527–1541 c Indian Academy of Sciences
1527
1528
P K Jana et al.
contribution from cosmic rays. The lifetime of the excited species ranges from milliseconds to minutes depending upon the altitudes from which they emanate. Green and red lines of oxygen, yellow lines of sodium and OH bands are the main emissions during day, twilight and night time. Meinel (1950a) first identified rotational–vibrational band of OH airglow emission. Meinel (1950a, 1950b, 1950c) discovered various vibration– rotation bands of the OH radical in the night airglow. These are known as the Meinel (M) bands, viz., OH M(7, 4) band, OH M(6, 3) band, OH M(3, 1) band, OH M(4, 2) and OH(5, 3) R heads. OH M(7, 4) band, OH M(6, 3) band, OH M(3, 1) band, OH M(4, 2) band and OH M(5, 3) band have been identified near 7530, 8744, 6169, 6503, and 6165 cm−1, respectively. OH(8, 3) is the other important emission of airglow spectrum. Takahashi et al. (1974) identified OH(8, 3) band airglow emission at latitude of 23◦S. They also reported that nocturnal variation of intensity was correlated with that of a rotational temperature. Krassovsky and Shagaev (1974) observed the wave-like propagation of disturbances of rotational temperature of OH(8, 3). Takahashi et al. (1977) studied the diurnal and seasonal variation of intensity of OH(8, 3) emission from 1972 to 1974. It showed a significant seasonal effect. The OH(8, 3) emission was found to increase slightly during magnetic disturbances. The proposed excitation mechanism (Bates and Nicolet 1950) of OH(8, 3) line indicates that the intensity of OH(8, 3) line is affected with the variation of ozone concentration.
Ozone, though a very minor atmospheric constituent, plays an important role to control the chemical kinetics of troposphere, stratosphere and mesosphere. The global ozone assessment confirms that ozone is declining everywhere in smaller amount (Bojkov 1992). But Farman et al. (1985) first reported that dramatic decrease of ozone concentration takes place at Antarctica during spring time causing an ozone hole. Afterwards, it was verified by different investigators all over the world (Midya and Jana 2002).
Conventionally, it is assumed that there is an ozone hole when the ozone abundance is ≤220 Dobson units (D U) (1 DU = 0.001 atm cm) in a specific geographic place (WMO 2002). The 1997 monthly averaged column ozone from the total ozone mapping spectrometer (TOMS) is up to 25 DU lower than the TOMS climatological mean (1979–1996) and up to 20 DU below the previous record low values (Cordero and Nathan 2002). Kerr (1998) reported that the 1998 Antarctic ozone hole is the biggest one ever observed. Average area of ozone hole was 25.3 × 106 km2 in September and 20.6 × 106 km2 in October 1998. The area of Antarctic ozone hole (area of O3 < 220 DU)
increased (Uchino et al. 1999) steadily from 1979 to 1998 and the 2000 ozone hole was the largest on record (Bodeker et al. 2002). Averaged area of the Antarctic ozone hole, determined by the area enclosed by the 220 DU total ozone contour, increased (Madrigal and Peraza 2005) from 2.6 × 106 to 25.8 × 106 km2 for the month of September and from 2.7 × 106 to 16.7 × 106 km2 for the month of October, during 1982–2003. Several theories have been proposed for the Antarctic ozone hole. Chemical, dynamical and natural theories are mainly important and are explained in an earlier publication (Jana and Nandi 2005). If ozone hole is created at any place in the atmosphere, O3 concentration also decreases in other regions due to atmospheric diffusion and circulation (Jana and Nandi 2005).
Measurement of airglow emission can be used as an important tool in studying the behaviour of the ionosphere and the upper atmosphere basically on the dynamical–photochemical processes that control the species composition and energy balance (Krasnopolsky 1986; Haider et al. 1992; Slanger et al. 2001). OH airglow emissions can be used as tracers of gravity wave (GW) that play an essential role in determining the global circulation and thermal balance of the atmosphere. A realistic GW parameterization is important for accurate atmospheric model. Dynamic control of OH altitude/ temperature at high latitudes was supported by the anti-correlation between OH peak altitude and temperature found in SABER (Sounding of the Atmosphere using Broadband Emission Radiometry) data (Winick et al. 2009) and also between OH peak altitude and meridional wind strength (Dyrland et al. 2010). Measurement of OH airglow can be used to derive atomic hydrogen concentration if ozone density is known (Mlynczak et al. 1998) and the OH rotational temperature near the mesopause (Lowe and Turnbull 1995). The OH airglow emission can extensively be used for studying atmospheric temperature variation at mesospheric region (Greet et al. 1998; Bittner et al. 2000). The airglow OH(8-3) and (6-2) band rotational temperatures were measured and compared using two scanning photometer at Cachoeira Paulista (23◦S, 45◦W) in 1999. The rotational temperature were obtained from the ratio between the P1(5) and P1(3) in the case of (8-3) band and P1(4) and P1(2) lines for the (6-2) band. It was shown that both the temperature did agree well (Wrasse et al. 2004).
Airglow emission can be influenced by atmospheric parameters including temperature, vertical advection, diffusion and some chemical species. Moreover, its temporal and spatial distributions are often modulated by dynamical perturbation such as gravity waves, planetary waves, tides and
Yearly variation and annual cycle of TCO over New Delhi and Halley Bay
1529
so on. Stratospheric sudden warming (SSW), the most important event in the mid-winter polar stratosphere can perturb atmospheric temperature, winds and distribution of several atmospheric chemical constituents in the middle atmosphere (Sathiskumar and Sridharan 2009; Funke et al. 2010). Therefore, influence of variation of total column ozone on OH airglow emission is an important approach for investigating the coupling between stratosphere and mesosphere-lower thermosphere (MLT) region (Gao et al. 2011). Wiens and Weill (1973) on analysis of the diurnal, annual and solar cycle variations in OH nightglow reported that the diurnal variation patterns altered with latitude and season and OH nightglow intensity followed the solar activity. Batista et al. (1994) showed that the OH(9, 4) band intensity had a positive correlation with the F 10.7 index. Abreu and Yee (1989) on the basis of the seasonal variations in the OH(8, 3) nightglow emission pointed out that there was a strong semi-annual oscillation with maxima near the equinoxes in the OH nightglow. Marsh et al. (2006) mentioned that the OH nightglow was stronger than the OH day glow. Shephered et al. (2006) showed that a 1% increase in temperature led about 4% increase in OH emission and OH emission was linearly sensitive to atomic oxygen concentration on the bottom side of the atomic oxygen layer.
In this paper, the nature of variations of monthly, yearly and seasonal total column ozone (TCO) over New Delhi and Halley Bay has been presented from 1979 to 2005. The most and the least identical monthly and seasonal variations with that of yearly TCO have been identified for these stations. Annual cycle of monthly TCO over these two stations has also been depicted. From the excitation mechanism OH(8, 3) airglow emission, the volume emission rate for different altitudes are computed. From the volume emission rate curve, the intensity of OH(8, 3) has been calculated for the year 1979. Following this process, the intensity of the same line over two stations, namely, New Delhi, India which has comparatively less depletion in ozone concentration and Halley Bay (76◦S, 27◦W), a British Antarctic Survey station which has comparatively much more depletion in ozone concentration, have been calculated for other years, considering the fluctuation percentages of O3 concentrations assuming that the variation of OH intensity is unaffected by the density of atomic hydrogen. The nature of different type of variations of TCO and intensities of OH(8, 3) is compared over these two stations because the stations are associated with distinctly different rates of ozone depletion without considering the semiannual oscillation (SAO), annual oscillation (AO) and quasi-biennial oscillation (QBO). In our previous
publications (Jana and Nandi 2006; Jana et al. 2011), effect of long term TCO on intensities of Na 5893 ˚A nightglow line and lithium 6708 ˚A over Dumdum (22.5◦N, 88.5◦E) and Varanasi (25◦N, 83◦E) had been presented and compared with that at Halley Bay (76◦S, 27◦W), respectively which showed same type of excitation mechanisms of sodium and lithium airglow emissions having different types of their importance in mesosphere. In case of OH(8, 3) airglow emission, the excitation mechanism and the role of OH(8, 3) which is stated above are completely different from the sodium and lithium airglow emission.
2. Data and analysis
Total column ozone densities of different stations have been obtained from the website http://jwocky. gsfc.nasa.gov (Jana et al. 2010a, 2010b). Monthly mean ozone densities have been calculated from daily average value of ozone in DU for the stations, namely, New Delhi and Halley Bay. The yearly mean ozone densities have been calculated from monthly average value of ozone in DU. The mean ozone for December, January and February (DJF) provides winter (summer) ozone, March, April and May (MAM) constitute pre-monsoon (fall) values, June, July and August (JJA) make monsoon (winter) values and September, October and November (SON) comprise post-monsoon (spring) values for the station New Delhi (Halley Bay), respectively. Total ozone data has been measured by the satellites Nimbus-7 Total Ozone Mapping Spectrometer (TOMS), Earth probe TOMS and Ozone Monitoring Instrument (OMI). TOMS and OMI provide high resolution daily global information about the total ozone content of the atmosphere by measuring ultraviolet sunlight backscattered from the ground. TCO in this study includes retrievals from Nimbus 7 (November 1978 to May 1993) and Earth probe (July 1996 to present) total ozone mapping spectrometer (TOMS). Data from HALOE (halogen occultation experiment) are used in this first method to extend the vertical span of MLS (highest pressure level 46 hPa) using simple regression. This assimilation enables high resolution daily maps of tropospheric and stratospheric ozone which is not possible from solar occultation measurements alone, such as from HALOE or Stratospheric Aerosols and Gas Experiment (SAGE) (Jana et al. 2012).
3. Results and discussions
The proposed excitation mechanisms of OH(8, 3) band are as follows:
1530
P K Jana et al.
1. Bates–Nicolet mechanism (Bates and Nicolet 1950)
O + O2 + M →K1 O3 + M,
(1)
O3 + H →K2 O2 + OH∗ (3.32 ev) ,
(2)
OH∗ A→vv OH + hv,
(3)
where K1 = 1.5×10−34 exp (445/T) cm√6 S−1 (Stuhl and Niki 1971) and K2 = 1.5 × 10−12 T cm3 S−1 (Nicolet 1970).
2. Breig mechanism (Breig 1970)
H + M + O2 →K3 HO2 + M,
(4)
HO2 + O →K4 OH∗ + O2,
(5)
where K3 = 3.3 × 10−33 exp(800/T√) cm6 S−1 (Gattinger 1971) and K4 = 1.5 × 10−12 T cm3 S−1 (Gattinger 1971).
3. Krassovsky mechanism (Krassovsky 1956)
O2 + O + M →K5 O3 + M,
(6)
O + O3 →K6 O∗2 + O∗2,
(7)
O∗2 + H →K7 OH∗ + O,
(8)
where K5 = 1.5×10−32 cm6 S−1 (Midya et al. 1998) and K7 = 10 × 10−10 cm3 S−1 (Midya et al. 1998). K1, K2, K3, K4, K5, K6 and K7 are all reaction rate constants. Midya et al. (1998) have established that Bates–Nicolet mechanism is the predominant and appropriate excitation mechanism of OH emission.
According to Bates–Nicolet mechanism, ignoring quenching terms, the volume emission rate of OH* is given by:
n (OH∗) = K2 [O3] [H]
(9)
So, the volume emission rate of OH(8, 3) band will be as follows:
Q∗OH = A8,3K2 [O3] [H] / Avv . (10)
where Avv is the Einstein transition probability from vibrational level v to v .
A8,3 = 0.0296 S−1
(11)
Avv = 13.5 (Midya et al. 1998). (12)
The Einstein A-coefficients associated with the OH* vibrational emissions have been measured in the laboratory (Nelson et al. 1990). Uncertainties regarding the quenching lifetimes and the rate constants for the reactions with atomic O remain fairly large (Mlynczak et al. 1998) and make the interpretation of the airglow feature difficult (Llewellyn et al. 1978).
Using the number densities of O3 and H, the volume emission rates of OH(8, 3) band for different altitudes have been calculated with the help of the equation (10). It attains maximum value at an altitude of 80 km. Altitudinal number densities of O3 and H and volume emission rates of OH(8, 3) band have been shown in table 1. Intensity has then been calculated from the volume emission rate curve with the help of the following equation:
Intensity = 1 × layer thickness 2 × peak volume emission rate. (13)
The value of layer thickness was 14.8 km and peak volume emission rate was 46 × 102 cm−3 s−1 for normal volume emission rate curve shown in figure 1. Thus, the intensity of OH(8, 3) band became 34.04 KR (KiloRayleigh) (1R = 1.0 × 105 cm−2 s−1). The number densities of H and O3 have been taken from Jacchia (1977). The OGOsatellite mass spectrometer launched in 1969 provided the first measurements of the densities of N2, O and He in the thermosphere. The observed variations in composition did not agree with Jacchia model. Accuracy may be improved with the corresponding data produced from MSIS (Mass Spectrometer and incoherent Scatter) model for various geographical, temporal and solar conditions, but pattern of variations of yearly, seasonal and annual cycle of OH intensities would be unaltered. The latest model, MSIS-86 was chosen for CIRA (COASPER International Reference) 1986. The database for MSIS-86 consists of composition, temperature and density data with in situ thermospheric measurements as well as rockets and ground based scatter stations (Marcos 1987). Gao et al. (2010) had also calculated the mean OH nightglow emission rate at the altitude of 88 km, the temperature and [O3] at 88 km which were observed by SABER, but they did not use [O] and [H] data measured by SABER because of large errors. They found that the distribution of the OH nightglow emission rate at 88 km, the peak emission rate (Vmax), intensity (I) and [O3] are similar to one another. Thus, they also concluded that the seasonal variations of temperature, [O], and [O3] played an important role in the seasonal variation of OH nightglow emission, Vmax and I. The TIMED (Thermosphere, Ionosphere, Mesosphere, Energetics, and Dynamics) satellite was launched on 7 December. The height of the TIMED circular orbit is about 625 km and the inclination is 74.1◦. The SABER, one of the four instruments onboard the TIMED satellite directly measures atmospheric emissions, such as OH airglow emission, O2 airglow emission and NO airglow emission over a broad spectral range using a multichannel infrared
Yearly variation and annual cycle of TCO over New Delhi and Halley Bay
1531
8.52 30.79 48.41 59.34 65.92 62.98 56.4 49.59 46.06 40.65 36.07 31.49 27.73 22.68 18.09 13.28
Halley Bay cm−3 s−1× 10−2
11.75
16.02
20.07
25.45
27.87
31.93
35.98
40.77
43.89
49.92
57.74
58.34
52.52
42.85
27.25
7.54
New Delhi cm−3 s−1× 10−2
Volume emission rates(Q) of OH(8, 3)
11.3
15.4
19.3
23.6
26.8
30.7
34.6
39.2
42.2
48
53.6
56.1
50.5
41.2
26.2
7.25
Normal cm−3 s−1
n(O3) × 10−8 Halley Bay 3.76 3.29 2.94 2.47 2.12 1.65 1.53 1.41 1.36 1.27 1.18 1.2 1.22 1.25 1.27 1.29
1.14
1.12
1.1
1.08
1.06
1.04
1.12
1.21
1.25
1.35
1.46
1.87
2.18
2.6
2.91
3.33
n(O3) × 10−8 New Delhi
Number densities (atoms/cc)
radiometer and indirectly measures atmospheric parameters, such as temperature, atmospheric density, ozone density, atomic oxygen density and so on.
Variations of yearly mean ozone concentrations at New Delhi and Halley Bay have been presented in figures 2 and 3, respectively, from 1979 to 2005. The nature of variations of ozone concentrations for each month for different years has been compared with the variation of yearly mean ozone concentrations. It has been observed that the variations of ozone concentrations for all months and variation of yearly mean ozone values followed nearly the same trend. The nature of variation of mean ozone values during the month of August from 1979 to 2005 was the most identical with the variation of yearly mean ozone values for the same period and the variation of mean ozone values during the month of December was the least identical with the variation of yearly mean ozone values for the same period at New Delhi. It has also been verified by the value of coefficient of correlation as depicted in figure 4 that depicts the variation of correlation coefficients with months at New Delhi (29◦N, 77◦E) and at Halley Bay (76◦S, 27◦W) from 1979 to 2005. The coefficient of correlation between August ozone mean values with yearly mean values was the maximum (0.82). It was the minimum for December ozone mean values (0.35). The yearly mean ozone concentration as well as the concentrations of ozone for every month was gradually decreasing from 1979 to 2005 at different rates at New Delhi. The rate of yearly mean ozone depletion was 0.3629 DU per year. It was 0.2102 and 0.8053 DU per year for the months of August and December, respectively. Therefore, the variation of August concentration of ozone mostly controlled the variation of annual TCO over New Delhi from 1979 to 2005 as the rate of ozone fall in August from 1979 to 2005 was the closest to that of annual TCO.
But in case of Halley Bay, the nature of variation of mean ozone values during the month of September from 1979 to 2005 was the most identical with the variation of yearly mean ozone values for the same period and the variation of mean ozone values during the month of April was the least identical with the variation of yearly mean ozone values for the same period. It has also been verified by the value of coefficient of correlation as shown in figure 4. The coefficient of correlation between September ozone mean values with yearly mean values was the maximum (0.97). It was the minimum for April ozone mean values (0.51). The yearly mean ozone concentration as well as the concentrations of ozone for every month was gradually decreasing from 1979 to 2005 at different rates. The rate of yearly mean ozone
11.3
15.4
19.3
23.6
26.8
30.7
34.6
39.2
42.2
48
53.6
56.1
50.5
41.2
26.2
7.25
QOH(8, 3) × 10−2
n(H) × 10−8 0.51 2.1 3.7 5.4 7 8.6 8.3 7.9 7.6 7.2 6.9 5.9 5.1 4.1 3.2 2.3
n(O3) × 10−8 3.2 2.8 2.5 2.1 1.8 1.4 1.3 1.2 1.16 1.08 1 1.02 1.04 1.06 1.08 1.1
Table 1. Volume emission rates of OH(8, 3).
Altitude (km) 75 76 77 78 79 80 81 82 83 84 85 86 87 88 89 90
1532
P K Jana et al.
92
90
88
Normal
New Delhi
86
Halley Bay
84
Altitude (km)
82
80
78
76
74
0
10
20
30
40
50
60
70
Volume emission rate of OH (8, 3) x 10 -2(cm -3 s-1 )
Figure 1. Altitudinal variations of volume emission rates of OH(8, 3) band at New Delhi (29◦N, 77◦E) and at Halley Bay (76◦S, 27◦W).
depletion was 2.684 DU per year. It was 4.7434 and 1.0914 DU per year for the months of September and April, respectively. So, the variation of yearly mean TCO over Halley Bay was controlled by that of September ozone values.
300
290
280
Seasonal variations of ozone densities at New Delhi reveal the most identical variation in DJF (winter) and least identical variation in SON
350 Apr
Sep
Mean
300
Fall
Spring
Density of ozone (DU) at New Delhi (29oN, 77oE) Density of ozone (DU) at Halley Bay (76 o S, 27o W)
270 250
260
250
240
230
Aug
Dec
220
Mean
Winter
210
Post-monsoon
200 1979 1982 1985 1988 1991 1994 1997 2000 2003 Year
200
150
100 1979 1982 1985 1988 1991 1994 1997 2000 2003 Year
Figure 2. Variation of ozone concentration at New Delhi (29◦N, 77◦E) from 1979 to 2005.
Figure 3. Variation of ozone concentration at Halley Bay (76◦S, 27◦W) from 1979 to 2005.
Coefficient of correlation between monthly mean and yearly mean ozone variation during 1979 to 2005
Ozone density (DU)
Yearly variation and annual cycle of TCO over New Delhi and Halley Bay
1533
1
380
0.9
0.8
330
0.7
0.6
0.5
280
0.4
0.3
0.2 New Delhi Halley Bay
0.1
230
0 Jan Feb Mar Apr May Jun Jul Aug Sep Oct Nov Dec
Months
180
New Delhi Halley Bay
Figure 4. Variation of correlation coefficients with months at New Delhi (29◦N, 77◦E) and at Halley Bay (76◦S, 27◦W) from 1979 to 2005.
(post-monsoon) with yearly mean variation. The rate of ozone depletion was 0.0763 and 0.028 DU per year in winter and post-monsoon, respectively. But, in case of Halley Bay, the most identical seasonal variations of ozone were observed in SON (spring), while the least identical seasonal variation in MAM (fall) with yearly mean ozone variation. The rate of ozone decline was 0.7174 and 0.159 DU per year in spring and fall, respectively.
Annual cycle of ozone concentrations for the stations at New Delhi and Halley Bay for the period 1979–2005 have been shown in figure 5, respectively. At New Delhi, ozone concentration attained the maximum value for the months of June and July. The minimum ozone concentration occurred for the months of December and January. Ozone concentration gradually increased from the month of January, attained its maximum for the period of June and July, then gradually decreased and reached its minimum value for the month of December.
In case of Halley Bay, ozone concentration attained the maximum value for the months of December and January. The minimum ozone concentration occurred at the months of September and October. Maximum ozone concentration occurred during the month of January, then gradually decreased, attained minimum for the month of September–October and then gradually increased. At both the stations, annual cycle of ozone densities for every year and their mean annual cycle followed nearly the identical variations.
Equation (10) clearly reveals that the volume emission rate of OH(8, 3) band is directly proportional to the concentrations of H and ozone
130
JAN
AR M
AY M
JUL SEP
NOV
Months
Figure 5. Annual cycle of ozone concentration at New Delhi (29◦N, 77◦E) and Halley Bay (76◦S, 27◦W).
(O3 + H → OH* + O2) with the reaction rate increasing with increasing temperature. O3 is produced from the reaction O + O2 + M → O3 + M and is destroyed mostly by the reaction O3 + H* → OH* + O2 and O + O3 → O2 + O2. The destruction of ozone due to the reaction with H is larger than the reaction with O by several orders of magnitude below 95 km (Xu et al. 2010). So, the contribution of producing OH airglow is somewhat nullified by the destruction of O3 that produces OH airglow. The production of O3 and consequent OH nightglow emission at mesosphere are proportional to the atomic oxygen density, thus OH airglow emission is influenced by atomic oxygen, ozone densities and also by atmospheric temperature. Ward (1999) reported that the OH nightglow is approximately proportional to the volume mixing ratio of O. Marsh et al. (2006) indicated that the transport of O is responsible for the annual cycle of the SABER OH emissions at higher latitudes. Xu et al. (2010) pointed out that the SABER OH nightglow brightness and temperature near the equator were positively correlated below about 94 km and negatively correlated above. The concentration of ozone in stratosphere varies in considerable amount from year to year, as well as from month to month. This stratospheric variation of ozone may influence the mesospheric altitudinal concentration of ozone. On the basis of recent study on the
Table 2. Yearly variation of intensity of OH(8, 3) at New Delhi and Halley Bay.
Year
Mean O3 (DU) at New Delhi
O3 fluctuation % from mean at New Delhi
Mean O3 (DU) at Halley Bay
O3 fluctuation % from mean at Halley Bay
Peak volume emission
rate OH(8, 3) at
New Delhi cm−3 s−1
1979 1980 1981 1982 1983 1984 1985 1986 1987 1988 1989 1990 1991 1992 1993 1994 1995 1996 1997 1998 1999 2000 2001 2002 2003 2004 2005
287.81 280.13 285.11 289.69 278.07 279.13 267.1 276.24 275.4 270.21 283.35 279.64 283.3 275.74 265.63 277.33 273.8 270.22 275.87 278.16 272.39 276.11 278.42 270.95 277.45 296.7 274.22
4.007 1.225 3.03 4.687 0.487 0.87 −3.476 −0.173 −0.477 −2.428 2.395 1.055 2.348 0.058 −4.911 −0.852 1.005 −2.348 −0.307 0.513 −1.568 −0.22 0.614 −2.085 0.263 −2.54 −0.907
300.54 299.48 294.94 286.14 286.56 271.33 264.93 267.56 258.03 279.77 261.99 251.04 254.01 250.08 251.29 233.57 237.84 242.1 252.6 227.91 228.39 236.13 227.81 253.04 226.09 234.09 227.81
17.5 17.08 15.31 11.87 12.03
6.08 3.37 4.61 0.88 9.38 2.43 −1.85 −0.69 −1.95 −1.76 −8.68 −7.01 −5.35 −1.24 −10.89 −10.71 −7.68 −10.94 −1.07 −11.37 −8.36 −10.94
58.34 56.79 57.79 58.73 56.37 56.59 54.15 56 55.83 54.74 57.45 56.69 57.42 56.13 53.35 55.62 55.53 54.78 55.93 56.39 55.22 55.98 56.45 54.93 56.23 54.68 55.59
Peak volume emission rate OH(8, 3) at Halley Bay cm−3 s−1
65.92 65.68 64.69 62.76 62.85 59.51 57.99 58.69 56.39 61.36 57.46 55.06 55.71 55 55.11 51.23 52.17 53.1 55.4 49.99 50.09 51.79 49.96 55.5 49.72 51.4 49.96
Intensity of OH(8, 3) line at New Delhi KR
35.4 34.46 35.07 35.64 34.21 34.34 32.86 33.98 33.88 33.21 34.86 34.4 34.84 34.06 32.37 33.75 33.7 33.24 33.93 34.21 33.51 33.97 34.25 33.33 34.13 33.18 33.73
Intensity of OH(8, 3) line at Halley Bay KR
39.99 39.85 39.25 38.08 38.14 36.11 35.19 35.61 34.34 37.23 34.87 33.41 33.81 33.38 33.44 31.09 31.65 32.22 33.62 30.33 30.39 31.43 30.32 33.68 30.17 31.19 30.32
P K Jana et al.
1534
Table 3. Seasonal variation of intensity of OH(8, 3) from 1979–2005 at New Delhi.
Yearly variation and annual cycle of TCO over New Delhi and Halley Bay
Year
Amount of O3(DU) in winter
O3 fluctuation
% from mean in winter
Intensity of OH(8, 3) in winter KR
Amount of O3
(DU) in pre-monsoon
O3 fluctuation
% from mean in pre-monsoon
Intensity of OH(8, 3) in pre-monsoon
KR
Amount of O3 (DU) in monsoon
O3 fluctuation
% from mean in monsoon
Intensity of OH(8, 3) in monsoon
KR
Amount of O3
(DU) in post-monsoon
O3 fluctuation
% from mean in post-monsoon
Intensity of OH(8, 3) in post-monsoon
KR
1979 1980 1981 1982 1983 1984 1985 1986 1987 1988 1989 1990 1991 1992 1993 1994 1995 1996 1997 1998 1999 2000 2001 2002 2003 2004 2005
290.33 270.95 284.84 282.59 274.61 285.28 259.69 274.01 263.21 269.61 279.51 277.43 275.78 267.14 256.55 276.54 267.78 259.03 265.15 270.86 263.18 268.55 265.92 258.96 276.65 257.8 263.96
7.29 0.13 5.27 4.43 1.49 5.43 −4.03 1.26 −2.73 −0.36 3.3 3.21 1.92 −1.27 −5.19 5.6 −1.04 −4.27 −2.01 3.39 −2.73 −0.75 −1.72 −2.05 2.24 −4.73 −2.45
36.52 34.08 35.83 35.55 34.55 35.89 32.67 34.47 33.11 33.92 35.16 35.13 34.69 33.61 32.27 35.95 33.69 32.59 33.36 35.19 33.11 33.78 33.45 33.34 34.8 32.43 33.21
299.8 292.46 296.46 310.88 281.68 287.25 269.19 288.13 293.21 272.29 290.6 289.23 297.21 291.94 274.43 287.48 287.33 286.52 285.72 290.17 268.56 289.65 296.57 276.89 288.89 276.8 290.11
4.31 1.76 3.16 8.17 −1.99 −0.05 −6.33 0.26 2.03 −5.24 1.17 0.64 3.42 1.6 −4.51 0.03 −0.02 −0.03 −0.58 0.97 −6.55 0.79 3.19 −3.65 0.52 −3.68 0.95
35.51 34.64 35.12 36.82 33.36 34.02 31.88 34.13 34.73 32.26 34.44 34.25 35.2 34.58 32.5 34.05 34.03 33.94 33.84 34.37 31.81 34.31 35.13 32.79 34.22 32.78 34.36
287.86 284.27 283.2 292.17 282.13 281.9 272.77 274.94 283.94 273.93 286.78 280.32 286.87 280.46 273.77 277.75 276.53 275.32 278.48 283.15 283.75 284.98 284.59 278.68 282.28 280.51 282.49
2.35 1.07 0.69 3.35 0.38 0.23 −3.02 −2.23 0.96 −2.59 1.97 −0.33 1.88 1.34 −2.66 −1.24 −1.68 −2.11 −0.98 0.68 0.89 1.33 1.19 −0.91 0.36 −0.26 0.44
34.84 34.4 34.27 35.24 34.16 34.12 32.95 32.28 34.37 33.16 34.71 33.93 34.68 34.5 33.13 33.62 33.477 33.32 33.71 34.27 34.34 34.49 34.45 33.37 34.16 33.95 34.19
273.24 272.78 275.93 273.11 268.56 262.07 266.74 267.86 261.13 264.99 272.99 271.58 273.33 263.43 257.97 267.55 263.54 260.02 274.13 263.74 274.06 261.25 266.44 269.26 261.99 263.68 260.29
2.3 2.13 3.31 2.25 0.55 −1.88 0.13 0.28 −2.67 0.79 2.21 1.67 2.33 1.37 3.42 0.17 −1.33 −2.65 2.63 −1.26 2.61 −2.19 −0.25 0.81 1.91 −1.28 −2.51
34.82 34.77 35.17 34.8 34.23 33.4 34.08 34.14 33.13 34.31 34.79 34.61 34.83 34.51 35.2 34.1 33.59 33.14 34.93 33.61 34.93 33.29 33.95 34.32 34.69 33.6 33.19
1535
Table 4. Seasonal variation of intensity of OH (8, 3) from 1979–2005 at Halley Bay.
Year
Amount of O3 (DU) in Summer
O3 fluctuation
% from mean in Summer
Intensity of OH(8, 3) in Summer KR
Amount of O3
(DU) in Fall
O3 fluctuation
% from mean in
Fall
Intensity of OH(8, 3) in Fall KR
1979 1980 1981 1982 1983 1984 1985 1986 1987 1988 1989 1990 1991 1992 1993 1994 1995 1996 1997 1998 1999 2000 2001 2002 2003 2004 2005
320.19 332.7 325.95 314.14 326.53 311.3 302.05 298.94 297.21 308.26 299.85 284.85 300.78 295.53 296.48 288.29 288.35 288.41 299.52 253.5 262.71 284.39 273.54 286.13 284.01 278.74 270.89
8.43 12.66 10.37
6.38 10.57
5.41 2.43 1.23 0.64 4.39 1.54 3.54 1.85 0.07 0.4 −2.38 −2.36 −2.34 1.43 −14.16 11.03 3.7 −7.37 −3.11 3.83 −5.61 −8.27
36.88 38.35 37.57 36.21 37.64 35.88 34.87 34.46 34.26 35.53 34.56 35.25 34.67 34.06 34.18 33.23 33.24 33.24 34.53 29.22 37.79 35.19 31.53 32.98 35.34 32.28 31.22
293.79 299.26 279.5 287.37 287.7 278.83 275.28 251.98 280.33 279.08 275.21 269.34 263.16 278.78 277.4 274.28 272.53 270.81 269.05 269.99 263.66 260.69 258.77 256.13 252.16 251.14 252.1
8.24 10.26
2.98 5.88 2.68 2.73 1.42 −7.16 3.28 2.82 1.4 −0.76 −3.04 2.71 2.2 1.05 0.41 −0.22 −0.87 −0.52 −2.86 −3.95 −4.66 −5.6 −7.1 −7.47 −7.12
36.84 37.53 35.05 36.04 34.95 34.97 34.52 31.36 35.16 34.99 34.52 33.78 33.01 34.96 34.79 34.4 34.18 33.97 33.74 33.86 33.07 32.7 32.45 32.14 31.62 31.5 31.62
Amount of O3 (DU) in Winter
289.61 290.15 289.03 289.93 272.82 265.78 259.28 264.22 262.08 268.19 254.2 243.29 238.32 238.9 252.88 205.51 218.87 232.23 251.58 229.3 231.53 221.46 216.99 226.34 198.6 224.36 210.03
O3 fluctuation
% from mean Winter
17.66 17.88 17.43 17.8 10.84
7.98 5.34 7.35 6.48 8.96 3.28 −1.15 −3.17 2.94 2.74 −16.5 −11.08 5.65 2.21 −6.84 −5.93 −10.02 −11.84 8.04 19.31 −8.84 −14.67
Intensity of OH(8, 3) in Winter
KR
40.05 40.13 39.97 40.1 37.73 36.76 35.86 36.54 36.25 37.09 35.16 33.65 32.96 35.04 34.97 28.42 30.27 35.96 34.08 31.71 32.02 30.57 30.01 36.78 40.6 31.03 29.05
Amount of O3
(DU) in Spring
298.58 275.82 285.29 259.11 259.2 229.42 220.94 255.11 192.49 263.53 218.68 206.65 213.78 189.92 178.39 166.21 171.59 176.97 190.04 158.87 155.67 177.97 161.92 243.56 171.98 183.32 178.21
O3 fluctuation
% from mean in Spring
41.95 31.04 35.54 23.1 23.14
8.99 4.96 21.98 8.55 25.2 3.89 −1.82 1.56 −9.77 −15.25 −21.03 18.49 −15.92 −9.72 −24.52 −26.04 −15.45 −23.07 15.71 −18.3 −12.91 −15.34
Intensity of OH(8, 3) in Spring KR
48.32 44.73 46.14 41.9 41.92 37.1 35.73 41.52 36.95 42.62 35.36 33.42 34.57 30.71 28.85 26.88 40.33 28.62 30.73 25.69 25.18 28.78 26.19 39.39 27.81 29.65 28.82
P K Jana et al.
1536