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Measurement of the OH rotational temperature at Mawson, East Antarctica
Planet. Space Set., Vol. 31, Printed in Great Britain.
00324633/83 $3 00 + 0.00
No. 8, pp. 923 932, 1983
Pergamon Press Ltd.
MEASUREMENT OF THE OH ROTATIONAL TEMPERATURE AT MAWSON, EAST ANTARCTICA
Antarctic
Division,
Department
L.C. STUBBS, J. S. BOYD and F. R. BOND of Science and Technology, Channel Highway, Australia
(Received injinulform 3 February
Kingston,
Tasmania,
7150,
1983)
Abstract-Measurements of the hydroxyl rotational temperature for the (8,3) Meinel band observations made at Mawson, East Antarctica (67” 36’S, 62” 53’ E) over the austral winter values of the rotational temperature are given for 54 nights. The average value lies in the range measured temperatures appear lower than those that have been reported at similar latitudes
are reported for of 1979. Mean 16c170 K. The
in the Northern Hemisphere. A gradual decrease in the value of the temperature throughout the course of the evening is the only diurnal trend observed. There is little evidence for any impulsive heating associated with aurora1 activity. INTRODUCTION
discovery by Meinel (1950a) of the rotationalvibrational bands of hydroxyl in the night airglow has been followed by many observations of the occurrence, morphology, intensity and dynamics of these emissions. In particular, the rotational temperature is believed to provide a reasonable measure of the temperature in the 8&100 km altitude range (Wallace, 1962). Several studies have been carried out of the distribution and variation of the temperature so measured. Variations in intensity and rotational temperature divide -naturally into those which appear related to diurnal and seasonal parameters and those which occur irregularly, apparently in response to some transient phenomena. Study of these variations should be expected to provide tests of models of upper atmosphere circulation and photochemistry. Principal features of the observed diurnal variation of intensity as reported in the literature are :
The
6) a decrease in intensity from the night-time value through morning twilight was first found from balloon-borne measurements by Lytle and reported by Noxon (1967). Similar results, also from balloon-borne measurements, are reported by Moreels et al. (1973a, b) ; (ii) a general decrease in intensity through the night hours. This effect is not always observed. At Calgary(invariant latitude 58” N), Harrison et al. (197 1) report that while occasionally a decrease in overall intensity is sometimes observed through the night hours, sometimes also there is an increase or a minimum around midnight. From observations made using an extensive network of stations, Wiens and Weill (1973) find a strong 923
latitudinal dependence of the occurrence of this nighttime decrease in intensity, with the effect being greatest at low latitudes and zero in the polar cap. However, it is pointed out by Wiens and Weill that there is great variability in the diurnal behaviour at middle latitudes, decreasing the significance of average behaviour. Such variability from night to night is certainly borne out by the observations of Harrison et al. in which four characteristically different variations were observed over successive nights. Observations on one night at Fort Churchill (invariant latitude 70” N) by Moreels et al. (1973a) show a decrease in intensity during the evening twilight in accordance with theoretical predictions, followed by a steady increase in intensity through the night.
Variations in rotational temperature Quasiperiodic fluctuations in rotational temperature on a time scale of approximately 1 h have been reported by several authors (Krassovsky, 1972; Krassovsky and Shagaev, 1974, 1977; Harrison et al., 1971 ; Armstrong, 1975). Impulsive fluctuations with a similar time scale have also been reported by Krassovsky (1972), Armstrong (1975) and Noxon (1978), among others. These impulsive events are attributed to the effect of gravity waves propagating from a high latitude region towards lower latitudes. Seasonal variations have also been reported (Harrison et al., 1971; Wiens and Weill, 1973).
Observutional proyram A program of measurement of the OH rotational temperature was begun in 1979 at the Australian National Antarctic Research Expedition station Mawson (67’ 36’S, 62” 53’E). The program was
924
L. c. STUHRS et al.
intended to monitor the OH emissions term basis with two principal aims :
on a fairly long
(i) to investigate
the variability of the intensity and temperature of the OH emissions on diurnal, seasonal and possibly solar cycle time scales ; (ii) to investigate any relationship between such variations and solar induced phenomena, particularly aurora1 and related activity. Many suggestions have been put forward to explain or predict mechanisms providing a causal relationship between solar induced phenomena, e.g. aurora and effects observed in the lower atmosphere. For example, Cole (1962) suggested that Joule heating associated with the intense aurora1 electrojet would produce a heat pulse which may propagate to lower altitudes. This search for direct evidence of a coupling mechanism between the thermosphere and middle atmosphere is associated with parallel statistical studies of such possible causal relationships. Among other conclusions, such studies show an apparent differencein behaviour related to soiar sector boundary crossings between the two hemispheres (Burns er al., 1980). The data discussed in this paper were obtained over the period June-September 1979.
maintained at a constant temperature, typicaliy 25°C. The detector is an EM1 9658A or 9659A photomultiplier in a refrigerated housing operating at - 50°C. Pulse counting circuitry was employed and the operating sequence was controlled by a minicomputer. Two or three period interference filters are used to isolate individual lines in the (8,3) band of the Meinel system around 730 nm. Half peak bandwidths are in the range 0.42-0.49 nm with peak transmissions in the range 3@40%. The wavelength of peak transmission of the filters as a function of tilt angle was determined and the tilt angles of the filters adjusted approximately monthly. Wavelength measurements were made using spectral lamps and a monochromator with a resolution of 0.01 nm. The neon lines at 724.52 nm and 743.89 nm were used as the standard reference wavelengths. An overall calibration of the system using a standardised white light source was carried out every second day. The filters were chosen to measure the intensities of the P,(2), P,(4) and P,(5) lines of the (8,3) band, the 557.7 nm 01 aurora1 line, the background at 735.0 nm and another emission, usually 630.0 nm 01. In operation, output pulses from the photomultiplier were accumulated for 60 s for each filter in rotation, thus allowing a temperature measurement to be completed every 7; min.
THEORY
INSTRUMENTATION
The measurements are made using a photometer consisting of a single telescope with a six position rotating filter wheel. The filters can be individually tilted to accurately set the wavelength ofthe passbands. The filter wheel is contained in a housing which can be
Significantly different values for the waveiength of the individual lines of the hydroxyl(8,3) band appear in the literature. Table 1 gives a list of experimental determinations of the wavelengths of the P,(2), P,(3), P,(4), P,(5) and P,(6) lines of this band from the
TABLE 1. WAVELENGTHMEASUREMENTS (IN AIR)OFTHEP,(2),
, P,(6)
LINESOF THE(8,3) HYDROXYLMEINELBAND
(Measured wavelengths in air)/nm Year
1950 1952 1955 1955 1959 1960 1962 1962 1978 1978
P,(2) 732.36 732.4 732.8 731.62 -731.64 731.57 731.50 731.63 -
P,(3) 734.82 734.8 734.9 734.11 734.2 734.10 734.02 733.94 734.02 734.036
P,(4)
737.58 737.6 737.4 736.2 736.97 736.95 736.74 -
-
* Accuracy claimed to be + 0.5 nm. 7 Accuracy claimed to be approximately & 0.05 nm. $ Accuracy claimed to be approximately 50.01 nm. 8 P,(2) value accurate to * 0.01 nm, P,(3) to f0.02 nm. 11 Accurate to k 0.027 nm.
P,(S)
P,(6)
Reference
740.85 740.8 740.9 739.3 740.19 740.10 740.12
744.45
Meinel(1950b) Small and Petrie (1952) McKinley et ai. (1955)” Chamberlain and Roe&r
144.5
743.87 743.58 743.70
Dufay (1959) Wallace (1960) Krassovsky et al. (1962)t Bass and Garvin (1962)t Meriwether et af. (1978)$ Burbidge et al. (1978) /I
(1955)
Measurement of the OH rotational temperature at Mawson, East Antarctica literature. The authors are grateful to Drs B. T. Lynds and J. W. Meriwether for private communications on this matter. It appears that the set of values given by Wallace (1960) may be the most accurate. Accordingly, values selected for the P,(2), P,(4), and P,(5) lines used in this study were 731.64, 736.96 and 740.18 nm respectively. Experimentally the relative intensities of the lines are given by
where Rj is the raw count recorded by the photometer minus the count due to the dark current of the photomultiplier tube, lj is the wavelength of the emission line, Z,(1) is the intensity of the standard white light source, Sj is the response of the photometer to this white light minus the count due to the dark current of the photomultiplier tube, B, is the relative intensity of the continuum background (the intensity of the background is assumed to be constant over the range of interest, 11730-740 nm), W$ is the equivalent bandwidth ofthe filter (Dandekar and Davis, 1973) and <(A) is the transmission of the filter divided by its transmission at the peak of the passband curve. A detailed description of the calibration procedure is given by Stubbs (1980). Theoretically the intensities of the lines (Mies, 1974) are given by I(J”, v” + J’, 0’) = N,,A(J”, v” + J’, u’)2(2J’ + 1)exp (-E,,(.l’)/(kT))
QuG'J where J’, J” are rotational quantum numbers (single primed quantum numbers refer to the upper state, double primed ones to the lower) ; v’, v” are vibrational quantum numbers ; N,. is the population of the upper vibrational state; A(J”, u” + J’, v’) is the Einstein coefficient for the indicated transition; E,.(Y) is the relative value ofthe energy of the rotational level with J = J’ of the upper vibrational state; k is the Boltzmann constant ; T is the rotational temperature; and Q,,(r) is the partition function of the upper vibrational state. The values of the Einstein coefficients are taken from Mies (1974) and those of E,,(Y) from Kendall and Clark (1979). The rotational temperature T is determined in the usual manner : either by taking the ratio of the relative intensity of any pair of lines, or else by fitting a straight line to the plot of
In[
I(J”, v” + J’, v’) (2J’
+
~)&Jft,
v”
+
J’,
v,)
1
vs E”W.
925
We have chosen to base our results for the rotational temperature on the measured relative intensities of the P,(2) and P,(4) lines. The rotational temperature, T, is determined from these two lines by T=
207.06 In (2.642R)
where R is the ratio of the intensity of the P,(2) line to the intensity of the P,(4) line. The corresponding relationship for the P,(2) and P,(5) lines is more sensitive to change in the value of the ratio R, but unfortunately the signal to noise ratio for the P,(5) line was too low for consistent and reliable results. Contamination of the P,(4) measurements by water vapour band absorption was not observed and is possibly due to there being low water vapour content in the upper atmosphere in polar regions. The measurements of all the hydroxyl lines of this band and of the background at 735.0 nm are subject to contamination from aurora1 emissions, e.g. the (5,3) band of N, First Positive Series near 735.0 nm. Data must be carefully checked for evidence of such contamination.
RESULTS
Method of analysis An initial selection of data for detailed analysis was made by rejecting data obtained during blizzard or heavily overcast conditions or which was obviously contaminated by aurora1 emissions. Rotational temperature data were subjected to Chauvenet’s rejection test (Pratt, 1961). In this test those points outside a certain number, N, of standard deviations are rejected as “bad” measurements. For example, for a sample of 100 points N = 1.98 whilst for 50 points N = 1.82. Of data so selected, there was only a small number of nights where all night the intensity of the continuum background was low and steady and the amount of aurora1 contamination was either low or minimal. Data from one of these nights (2 July) are illustrated in Fig. 1. Data from other nights are then of variable quality, from quite good to marginal. A typical example (23 July) is shown in Fig. 2. From approx. 17.00 L.M.T. (L.M.T. = U.T.+4h 12min)to23.00L.M.T.gooddata are recorded. Thereafter, contamination from aurora1 emissions is apparent and the values for the relative intensities of the P,(2) and P,(4) lines and the rotational temperature can no longer be regarded as meaningful. In the early part of the evening (17.00 L.M.T. to 23.00 L.M.T.) the relative intensities of the P,(2) and P,(4) lines vary quite dramatically between 3 and 12 units (intensity is measured in arbitrary units). The
926
L. C.
STUBBS
et al.
; 160 g 140 E 120 If 100
6
P(2)
Day
163
7 6 PI41 5
1600
2000 Local
2200 Mean
2400
0200
0400
0600
0600
Time
FI~.~.DATAFORONENIGHT(~JULY)ON~ICHTHEREWASVIRTUALLYNOAURORALACTIVITYASINDICA~DBY THERELATIVELYLOWANDCONSTANTBACKGROUNDINTENSITY. The relative intensity of the P,(2) and P,(4) lines is shown as well as the rotational temperature calculated
from
the ratio of the intensity of the two lines.
correlation (the value rotational a mean of
between the two OH lines is extremely good of the correlation coefficient is 0.98). The temperature remains fairly steady and yields 184.1 K with a S.D. of 6.4 K.
Seasonal and diurnal variations The mean temperatures for the nights from 4 June to 1 September 1979 on which rotational temperatures could be accurately measured are listed in Tables 2 and 3. The correlation coefficient between the relative intensities of the P,(2) and P,(4) lines is given for each night. The variation of the rotational temperature over the 3 months is shown in Fig. 3. Some authors have reported a maximum in the rotational temperature in winter (see the discussion by Wallace (1962)), whilst others have observed no seasonal variation (for example, Kvifte (1967)). Over the observational period of 3 months, a trend such as a maximum in the rotational temperature near the middle of winter should be detectable if it be there. None is discernible in the data reported here. To further examine whether any diurnal trends existed, hourly mean values of rotational temperature
and the number of points they are based upon are plottedinFig.4for thefirstandsecond halfofthewinter season. The results of this analysis are tabulated in Table 4. The decline near 02.00 L.M.T. in the number of points upon which the mean temperature is based is due to this being the time of maximum frequency of occurrence of aurorae. The only trend observed among the individual nights as illustrated in Figs. 1 and 2 was a gradual steady decrease in the rotational temperature during the course of the evening. The averaged data for 4 June-16 July show no apparent trend, whilst those for 17 July-l September exhibit a gradual steady decrease during the course of the evening. Some authors report a minimum near local midnight (for example, Shefov (1971)) whilst others observe no such trend. The gradual steady decrease in the rotational temperature during the course of the evening is the only trend apparent in the data recorded at Mawson. This trend is in agreement with that reported by Takahashi et al. (1974) at 23” S in Brazil. The data were also analysed into temperature intervals of 10 K to examine the distribution of the rotational temperature. Figure 5 shows the resultant
Measurement
of the OH rotational
temperature
at Mawson,
921
East Antarctica
220 y
200 160
%
160
p
r-w--
Day 204 /
Rejected
Data----~
I!
12
6 I
ii’ 2
LocalMearTlma
F1c.2.
DATA AS FORFIG. 1 BUT FOR 23 JULY,• N WHICH NIGHT AURORAL ACTIVITY COMPLETELY OISRUPTED MEASUREMENTS ATAPPROX. 23.20 L.M.T.
I
I
I
I zoo-
Mean TernperatureK 190-
f
Iso 140-
of
Number
0
I
I
I
Jlne
t
11
1
I
”
July
PoiVs
”
1’
I
’
1”
rl
hm
F1c.3. MEAN NIGHTLYROTATIONALTEMPERATIJREFORTHEPERIOD~JUNE-1 The number oftemperature measurements from which each mean is derived
SEPTEMBER.
is also plotted.
L. C.
928
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et al.
TABLE2. MEAN NIGHTLYTEMPERATURES FORTHEPERIOD 4 JUNETO 16 JULY. The correlation coefficient between the intensities of the P,(2) and P,(4) lines is given in the last column
Date
Mean temperature (K)
Standard deviation (K)
Number of points
Correlation coefficient
June
4 5 6 9 14 21 22 23 24 25 26 27 28 29 30
168.5 176.4 177.0 173.5 136.1 185.0 166.6 184.4 183.2 181.1 173.9 170.2 158.6 145.5 140.9
7.3 24.5 10.2 10.2 10.0 14.7 8.6 9.9 9.9 10.6 8.9 11.1 13.0 12.7 11.0
65 109 25 45 54 65 31 81 71 91 26 115 78 82 84
0.97 0.48 0.68 0.73 0.91 0.90 0.86 0.95 0.96 0.92 0.95 0.29 0.85 0.77 0.93
July
1 2 11 12 14 15 16
140.2 139.8 183.0 170.3 170.7 154.2 156.1
9.5 8.1 13.6 9.8 9.1 11.6 14.6
107 132 60 32 47 27 67
0.94 0.97 0.81 0.74 0.92 0.78 0.84
Meon TemperatureK
4tbAne-t6ttlJuty
17thJuly-M saptamts3r
FIG. 4. HOURLYMEANS OFTHEMEASURU) ROTATIONAL TEMPERATURE OVERTHETWO PERIODS 4 JUNE-16JULY AND 17 JULY-~ SEP~MBER. The number of measurements from which each mean is derived is also plotted. The time is given in L.M.T.
Measurement
of the OH rotational
temperature
at Mawson,
East Antarctica
929
TABLE 3. MEAN NIGHTLY TEMPERATURES FOR THE PERIOD 17 JULY-~ SEPTEMBER. The correlation coefficient between the intensities of the P,(2) and P,(4) lines is given in the last column
Mean temperature (K)
Date July
August
September
17 18 21 22 23 24 2.5 26 27 28 30 31 2 4 9 11 13 14 15 16 20 21 22 23 24 25 26 27 28 30 31 1
Standard deviation
184.3 156.0 190.2 158.2 184.1 199.8 170.0 154.8 164.2 152.1 175.1 176.2 168.5 160.5 191.4 186.8 165.7 161.0 169.1 159.1 165.1 158.5 155.3 168.1 160.1 166.3 168.9 168.9 163.1 169.1 171.0 162.8
for the periods 4 June-16 July and 17 July1 September. For example, in the period 17 July-l September 26.0% of the temperature values lie in the range 16&l 70 K. The median value for each period lies in the range 16&170 K as does that for all data combined. The data for the period 4 June-16 July show peaks in the distribution near 140 and 180 K. This double peak appears to reflect variations in mean temperature from night to night over that period. distribution
Possible evidence for aurora1 heating
There is generally little evidence for any increase in rotational temperature caused by aurora1 activity. Data from one night (25 June) are shown in Fig. 6. In the period before the aurora1 display, there is a noticeable steady decrease in the values of the rotational temperature, as discussed above, and likewise after the aurora1 display the temperatures
Number Of
points
(K) 14.7 15.2 11.3 12.9 6.4 11.4 14.2 13.7 8.3 16.1 16.5 14.7 13.5 9.3 15.1 7.1 9.7 5.7 8.5 8.7 9.3 10.3 8.8 12.3 10.2 3.0 10.4 6.5 16.5 9.7 11.5 8.9
25 59 89 95 48 45 109 46 40 80 62 81 51 20 62 56 45 70 44 92 22 22 60 100 41 12 50 27 56 86 66 42
Correlation coefficient 0.90 0.85 0.92 0.94 0.98 0.89 0.81 0.97 0.81 0.93 0.94 0.78 0.89 0.83 0.64 0.80 0.76 0.90 0.66 0.90 0.82 0.89 0.90 0.96 0.87 0.87 0.46 0.94 0.89 0.91 0.78 0.90
display the same gradual decrease. However, there is a marked increase of approx. 30 K after the aurora1 activity. Whilst possibly indicative of aurora1 heating, the evidence provided by this single event is hardly conclusive. For instance, this result can be compared with data obtained the following evening. A more intense aurora1 display occurred over Mawson from 23.45 L.M.T. to 03.45 L.M.T. In the period before and after this display, meaningful OH measurements could only be made from 17.40 L.M.T. to 18.52 L.M.T. and from 04.59 L.M.T. to 07.07 L.M.T. respectively. The mean of the eleven points in the period before the aurora1 display is T = 169.6 K with e = 6.7 K. For the fifteen points in the interval after the aurora1 display, the mean temperature is T = 177.1 K with c = 9.2 K. This is either indicative of no aurora1 heating, or else that there was heating prior to twilight before OH measurements commenced.
L. C. STCJBBS et al.
930
TABLE4. HOURLYMEANSFORTHEROTATIONAL TEMPERATURES MEASURED FROM4 JUNETO 16 JULYAND 17 JULYTO 1 SEPTEMBER.
Time intervals are at L.M.T. 4 June-16 JULY
Time interval (L.M.T.)
Mean temperature
Standard deviation
(K)
(K)
165.1 159.7 169.6 168.1 165.9 163.8 159.0 159.0 165.6 162.4 155.6 152.8 167.0 161.4 163.0 168.4 161.6 143.7
31.3 19.7 17.2 17.7 19.9 20.4 20.0 22.5 21.3 18.0 22.4 24.3 25.5 22.5 17.4 23.2 25.4 29.5
1X&1600 1600-1700 17W1800 18OG1900 190&2000 2OOG2100 210@2200 2200-2300 2300-2400 24WOlOO 01OcO200 020@0300 030&0400 040&0500 05WO600 060@0700 07OGO800 08KW900
Number of points 8 95 148 1.56 151 141 128 115 87 72 50 39 47 58 65 71 49 14
(a)
90
110
130
150
Rotational
90
II0
I30
I50
Rotational
170
190
temperature
170
190
temperature
210
230
K
210
K
17 July-l September
._
230
_
Mean temperature
Standard deviation
(K)
(K)
Number of points
171.8 173.4 169.3 173.6 174.0 171.1 166.2 164.5 163.0 162.7 164.4 164.4 165.0 164.2 171.0 166.5
9.1 15.6 17.3 16.0 18.9 16.5 17.7 20.1 16.7 20.8 18.6 16.1 13.3 16.1 19.9 19.8
13 119 206 200 200 158 139 133 108 73 98 99 113 121 83 26
Latitudinal considerations The study of OH airgiow emissions has mainly been confined to the Northern Hemisphere. Kvifte (1967) gave an extensive list of reports of measurements of the OH rotational temperature and all but two were in the latitudinal range of40-85” N. The noticeable difference to the results reported here is that, in general, the Northern Hemisphere rotational temperature values were much higher than those at Mawson. Most of the values of Kvifte’s list lie in the 21&250 K range. One exception is Noxon (1964) who studied the latitudinal dependence of the OH rotational temperature using a spectrometer installed in ajet aircraft. He reported 215, 170 and 160 K for the latitudinal ranges 62-69” N, 6977” N and 77-85” N respectively. The latter two values are similar to the values measured at Mawson. In the Southern Hemisphere there is little data for comparison. Armstrong (1975) reported values for the rotational temperature in the range 220-310 K in Australia (30” S) ; Blackwell et al. (1960) reported 293 K in Bolivia (16” S); and Takahashi and co-workers (Takahashi et al., 1974, 1979; Clemesha et al., 1979) reported values in the range 16&l 90 Kin Brazil (23” S).
FIG. 5. FREQUENCY OF OCCURRENCE0~ TEMPERATURE MEASUREMENTS IN 10 K INTERVALS OVERTHEPERIOD (a) 4 JUNE16 JULY; AND (b) 17 JULYA SEPTEMBER. The total number of points in period (a) is 1494 and in period
(b) is 1803.
Measurement
of the OH rotational
temperature
at Mawson,
Bat
East Antarctica
931
Day 176
IO-9-8--
7--
r Rejected
Data - - - -1
I
6-1
5-4-P(2) 3--
P(4)
2-I--
I
I400
1
I 1600
I
I 1800
1
I
I
2000
1
2200
I
twcl
I
2400
02c0
I
I 0400
I
I 0600
I
I 0600
Local ~Tinm Ftc.6. TEMPERATUREDATAFORONENIGHT MEASUREMENTSFORA
(25 JUNE)ONWHICHAURORALACTIVITYINTERRUPTEDTEMPERATURE PERK," OFAPPROX. 4 h, AFTER WHICH THETEMPERATUREMEASUREMENTRESUMED HIGHERVALUETHANBEFOKETHEDISTURBANCE.
The range of values measured in Brazil is in line with that measured at Mawson. Given the small number of measurements that have been made of the rotational temperature in the Southern Hemisphere, no conclusion can be drawn concerning any systematic latitudinal dependence of rotational temperatures.
CONCLUSION
The average rotational temperature for the OH (8,3) band emission observed at 67” S at Mawson, East Antarctica, during the winter of 1979 lies in the range 16&170 K. A multi-channel photometer was employed whereby a sampling rate for the rotational temperature of eight measurements per hour was possible. One event indicative of aurora1 heating was observed, but a
AT A
single observation must be regarded as inconclusive. The maximum in the rotational temperature in winter frequently observed in seasonal variation studies is not observed. The only diurnal trend observed is a gradual decrease in the value of the rotational temperature throughout the course of the evening. The small number of Southern Hemisphere measurements precludes comment at this stage on the latitudinal variation of the OH rotational temperature in the Southern Hemisphere. Acknowledgements~-The assistance of the members of the Mawson wintering party is gratefully acknowledged, in particular, A. Blake, P. Delaney, P. Magill, B. Vince and J. Wignall as well as N. Voloshinov, exchange scientist from the Soviet Antarctic Expedition. The authors are also grateful for assistance with the data processing provided by H. Burton (Antarctic Division) and the Bureau of Meteorology.
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REFERENCES Armstrong, E. B. (1975) J. atmos. terr. Phys. 37, 1585 Bass, A. M. and Garvin, D. (1962) J. molec. Spectrosc. 9, 114. Blackwell. D. E.. Ineham. M. F. and Rundle. H. N. (1960) ~ I Astrophys J. Ii,, IS. Burbidge, E. M., Smith, H. E. and Burbidge, G. R. (1978) Astrophys. J. 219,400. Burns, G. B., Bond, F. R. and Cole, K. D. (1980) J. atmos. terr. Phys. 42, 765. Chamberlain, J. W. and Roesler, F. L. (1955) Astrophys J. 121, 541. Clemesha, B. R., Kirchhoff, V. W. J. H., Simonich, D. M., Takahashi, H. and Batista, P. P. (1979) J. geophys. Rex 84, 6477. Cole, K. D. (1962) Aust. J. Phys. 15,223. Dandekar, B. S. and Davis, D. J., Jr. (1973) Appl. Opt. 12,825. Dufay, M. (1959) Ann. Gkophys. 15, 134. Harrison, A. W., Evans, W. F. J. and Llewellyn, E. J. (1971) Can. J. Phys. 49, 2509. Kendall, D. J. W. and Clark, T. A. (1979) J. Quant. Spectrosc. Radiat. Trarxfer 21,511. Krassovsky, V. I., Shefov, N. N. and Yarin, V. I. (1962) Planet. Space Sci. 9, 883. Krassovsky, V. I. (1972) Ann. Geophys. 28,739. Krassovsky, V. I. and Shagaev, M. V. (1974) Planet. Space Sci. 22, 1334. Krassovsky, V. I. and Shagaev, M. V. (1977) Planet. Space Sci. 25,200. Kvifte, G. J. (1967) Planet. Space Sci. 15, 1515. McKinley, J. D., Jr., Garvin, D. and Bondart, M. J. (1955) J. them. Phys. 23,784.
et al
Meinel, A. B. (1950a) Astrophys. J. 111,207. Meinel, A. B. (1950b) Astrophys. J. 111, 555. Meriwether, J. W., Jr.,Torr, D. G., Walker, J. C. G. andNier, A. 0. (1978) J. geophys. Res. 83, 3311. Mies. F. H. (1974) J. molec. Soectrosc. 53, 150. Moreels, G.: Jones, A. V. and Blamont, J. E. (1973a) Can. J. Phys. 51, 888. Moreels, G., Jones, A. V. and Blamont, J. E. (1973b) Planet. Space Sci. 21,1945. Noxon, J. F. (1964) J. geophys. Res. 69,4087. Noxon, J. F.(1967) Auroraand Airglow(Edited by McCormac, B. M.), p. 123. Reinhold, New York. Noxon, J. F. (1978) Geophys. Res. Lett. 5, 25. Pratt, L. G. (1961) Probability & Experimental Errors in Science. John Wiley, New York. Shefov, N. N. (1971) Planet. Space Sci. 19, 129. Small, R. and Petrie, W. (1952) Additional OH Lines in the AirglowSpectrum. Scientific Report No. AR-8, University of Saskatchewan. Stubbs, L. C. (1980) Deriving the Rotational Temperaturefrom Measurements of the (8-3) OH Meinel Band. Technical Memorandum No. 97. Antarctic Division, Kingston, Tasmania, Australia. Takahashi, H., Clemesha, B. R. and Sahai, Y. (1974) Planet. Space Sci. 22,1323. Takahashi, H., Batista, P. P., Clemesha, B. R.,Simonich,D. M. and Sahai, Y. (1979) Planet. Space Sci. 27, 801. Wallace, L. (1960) Astrophys. J. 132,894. Wallace, L. (1962) J. atmos. Sci. 19, 1. Wiens, R. H. and Weill, G. (1973) Planet. Space Sci. 21, 1011.
00324633/83 $3 00 + 0.00
No. 8, pp. 923 932, 1983
Pergamon Press Ltd.
MEASUREMENT OF THE OH ROTATIONAL TEMPERATURE AT MAWSON, EAST ANTARCTICA
Antarctic
Division,
Department
L.C. STUBBS, J. S. BOYD and F. R. BOND of Science and Technology, Channel Highway, Australia
(Received injinulform 3 February
Kingston,
Tasmania,
7150,
1983)
Abstract-Measurements of the hydroxyl rotational temperature for the (8,3) Meinel band observations made at Mawson, East Antarctica (67” 36’S, 62” 53’ E) over the austral winter values of the rotational temperature are given for 54 nights. The average value lies in the range measured temperatures appear lower than those that have been reported at similar latitudes
are reported for of 1979. Mean 16c170 K. The
in the Northern Hemisphere. A gradual decrease in the value of the temperature throughout the course of the evening is the only diurnal trend observed. There is little evidence for any impulsive heating associated with aurora1 activity. INTRODUCTION
discovery by Meinel (1950a) of the rotationalvibrational bands of hydroxyl in the night airglow has been followed by many observations of the occurrence, morphology, intensity and dynamics of these emissions. In particular, the rotational temperature is believed to provide a reasonable measure of the temperature in the 8&100 km altitude range (Wallace, 1962). Several studies have been carried out of the distribution and variation of the temperature so measured. Variations in intensity and rotational temperature divide -naturally into those which appear related to diurnal and seasonal parameters and those which occur irregularly, apparently in response to some transient phenomena. Study of these variations should be expected to provide tests of models of upper atmosphere circulation and photochemistry. Principal features of the observed diurnal variation of intensity as reported in the literature are :
The
6) a decrease in intensity from the night-time value through morning twilight was first found from balloon-borne measurements by Lytle and reported by Noxon (1967). Similar results, also from balloon-borne measurements, are reported by Moreels et al. (1973a, b) ; (ii) a general decrease in intensity through the night hours. This effect is not always observed. At Calgary(invariant latitude 58” N), Harrison et al. (197 1) report that while occasionally a decrease in overall intensity is sometimes observed through the night hours, sometimes also there is an increase or a minimum around midnight. From observations made using an extensive network of stations, Wiens and Weill (1973) find a strong 923
latitudinal dependence of the occurrence of this nighttime decrease in intensity, with the effect being greatest at low latitudes and zero in the polar cap. However, it is pointed out by Wiens and Weill that there is great variability in the diurnal behaviour at middle latitudes, decreasing the significance of average behaviour. Such variability from night to night is certainly borne out by the observations of Harrison et al. in which four characteristically different variations were observed over successive nights. Observations on one night at Fort Churchill (invariant latitude 70” N) by Moreels et al. (1973a) show a decrease in intensity during the evening twilight in accordance with theoretical predictions, followed by a steady increase in intensity through the night.
Variations in rotational temperature Quasiperiodic fluctuations in rotational temperature on a time scale of approximately 1 h have been reported by several authors (Krassovsky, 1972; Krassovsky and Shagaev, 1974, 1977; Harrison et al., 1971 ; Armstrong, 1975). Impulsive fluctuations with a similar time scale have also been reported by Krassovsky (1972), Armstrong (1975) and Noxon (1978), among others. These impulsive events are attributed to the effect of gravity waves propagating from a high latitude region towards lower latitudes. Seasonal variations have also been reported (Harrison et al., 1971; Wiens and Weill, 1973).
Observutional proyram A program of measurement of the OH rotational temperature was begun in 1979 at the Australian National Antarctic Research Expedition station Mawson (67’ 36’S, 62” 53’E). The program was
924
L. c. STUHRS et al.
intended to monitor the OH emissions term basis with two principal aims :
on a fairly long
(i) to investigate
the variability of the intensity and temperature of the OH emissions on diurnal, seasonal and possibly solar cycle time scales ; (ii) to investigate any relationship between such variations and solar induced phenomena, particularly aurora1 and related activity. Many suggestions have been put forward to explain or predict mechanisms providing a causal relationship between solar induced phenomena, e.g. aurora and effects observed in the lower atmosphere. For example, Cole (1962) suggested that Joule heating associated with the intense aurora1 electrojet would produce a heat pulse which may propagate to lower altitudes. This search for direct evidence of a coupling mechanism between the thermosphere and middle atmosphere is associated with parallel statistical studies of such possible causal relationships. Among other conclusions, such studies show an apparent differencein behaviour related to soiar sector boundary crossings between the two hemispheres (Burns er al., 1980). The data discussed in this paper were obtained over the period June-September 1979.
maintained at a constant temperature, typicaliy 25°C. The detector is an EM1 9658A or 9659A photomultiplier in a refrigerated housing operating at - 50°C. Pulse counting circuitry was employed and the operating sequence was controlled by a minicomputer. Two or three period interference filters are used to isolate individual lines in the (8,3) band of the Meinel system around 730 nm. Half peak bandwidths are in the range 0.42-0.49 nm with peak transmissions in the range 3@40%. The wavelength of peak transmission of the filters as a function of tilt angle was determined and the tilt angles of the filters adjusted approximately monthly. Wavelength measurements were made using spectral lamps and a monochromator with a resolution of 0.01 nm. The neon lines at 724.52 nm and 743.89 nm were used as the standard reference wavelengths. An overall calibration of the system using a standardised white light source was carried out every second day. The filters were chosen to measure the intensities of the P,(2), P,(4) and P,(5) lines of the (8,3) band, the 557.7 nm 01 aurora1 line, the background at 735.0 nm and another emission, usually 630.0 nm 01. In operation, output pulses from the photomultiplier were accumulated for 60 s for each filter in rotation, thus allowing a temperature measurement to be completed every 7; min.
THEORY
INSTRUMENTATION
The measurements are made using a photometer consisting of a single telescope with a six position rotating filter wheel. The filters can be individually tilted to accurately set the wavelength ofthe passbands. The filter wheel is contained in a housing which can be
Significantly different values for the waveiength of the individual lines of the hydroxyl(8,3) band appear in the literature. Table 1 gives a list of experimental determinations of the wavelengths of the P,(2), P,(3), P,(4), P,(5) and P,(6) lines of this band from the
TABLE 1. WAVELENGTHMEASUREMENTS (IN AIR)OFTHEP,(2),
, P,(6)
LINESOF THE(8,3) HYDROXYLMEINELBAND
(Measured wavelengths in air)/nm Year
1950 1952 1955 1955 1959 1960 1962 1962 1978 1978
P,(2) 732.36 732.4 732.8 731.62 -731.64 731.57 731.50 731.63 -
P,(3) 734.82 734.8 734.9 734.11 734.2 734.10 734.02 733.94 734.02 734.036
P,(4)
737.58 737.6 737.4 736.2 736.97 736.95 736.74 -
-
* Accuracy claimed to be + 0.5 nm. 7 Accuracy claimed to be approximately & 0.05 nm. $ Accuracy claimed to be approximately 50.01 nm. 8 P,(2) value accurate to * 0.01 nm, P,(3) to f0.02 nm. 11 Accurate to k 0.027 nm.
P,(S)
P,(6)
Reference
740.85 740.8 740.9 739.3 740.19 740.10 740.12
744.45
Meinel(1950b) Small and Petrie (1952) McKinley et ai. (1955)” Chamberlain and Roe&r
144.5
743.87 743.58 743.70
Dufay (1959) Wallace (1960) Krassovsky et al. (1962)t Bass and Garvin (1962)t Meriwether et af. (1978)$ Burbidge et al. (1978) /I
(1955)
Measurement of the OH rotational temperature at Mawson, East Antarctica literature. The authors are grateful to Drs B. T. Lynds and J. W. Meriwether for private communications on this matter. It appears that the set of values given by Wallace (1960) may be the most accurate. Accordingly, values selected for the P,(2), P,(4), and P,(5) lines used in this study were 731.64, 736.96 and 740.18 nm respectively. Experimentally the relative intensities of the lines are given by
where Rj is the raw count recorded by the photometer minus the count due to the dark current of the photomultiplier tube, lj is the wavelength of the emission line, Z,(1) is the intensity of the standard white light source, Sj is the response of the photometer to this white light minus the count due to the dark current of the photomultiplier tube, B, is the relative intensity of the continuum background (the intensity of the background is assumed to be constant over the range of interest, 11730-740 nm), W$ is the equivalent bandwidth ofthe filter (Dandekar and Davis, 1973) and <(A) is the transmission of the filter divided by its transmission at the peak of the passband curve. A detailed description of the calibration procedure is given by Stubbs (1980). Theoretically the intensities of the lines (Mies, 1974) are given by I(J”, v” + J’, 0’) = N,,A(J”, v” + J’, u’)2(2J’ + 1)exp (-E,,(.l’)/(kT))
QuG'J where J’, J” are rotational quantum numbers (single primed quantum numbers refer to the upper state, double primed ones to the lower) ; v’, v” are vibrational quantum numbers ; N,. is the population of the upper vibrational state; A(J”, u” + J’, v’) is the Einstein coefficient for the indicated transition; E,.(Y) is the relative value ofthe energy of the rotational level with J = J’ of the upper vibrational state; k is the Boltzmann constant ; T is the rotational temperature; and Q,,(r) is the partition function of the upper vibrational state. The values of the Einstein coefficients are taken from Mies (1974) and those of E,,(Y) from Kendall and Clark (1979). The rotational temperature T is determined in the usual manner : either by taking the ratio of the relative intensity of any pair of lines, or else by fitting a straight line to the plot of
In[
I(J”, v” + J’, v’) (2J’
+
~)&Jft,
v”
+
J’,
v,)
1
vs E”W.
925
We have chosen to base our results for the rotational temperature on the measured relative intensities of the P,(2) and P,(4) lines. The rotational temperature, T, is determined from these two lines by T=
207.06 In (2.642R)
where R is the ratio of the intensity of the P,(2) line to the intensity of the P,(4) line. The corresponding relationship for the P,(2) and P,(5) lines is more sensitive to change in the value of the ratio R, but unfortunately the signal to noise ratio for the P,(5) line was too low for consistent and reliable results. Contamination of the P,(4) measurements by water vapour band absorption was not observed and is possibly due to there being low water vapour content in the upper atmosphere in polar regions. The measurements of all the hydroxyl lines of this band and of the background at 735.0 nm are subject to contamination from aurora1 emissions, e.g. the (5,3) band of N, First Positive Series near 735.0 nm. Data must be carefully checked for evidence of such contamination.
RESULTS
Method of analysis An initial selection of data for detailed analysis was made by rejecting data obtained during blizzard or heavily overcast conditions or which was obviously contaminated by aurora1 emissions. Rotational temperature data were subjected to Chauvenet’s rejection test (Pratt, 1961). In this test those points outside a certain number, N, of standard deviations are rejected as “bad” measurements. For example, for a sample of 100 points N = 1.98 whilst for 50 points N = 1.82. Of data so selected, there was only a small number of nights where all night the intensity of the continuum background was low and steady and the amount of aurora1 contamination was either low or minimal. Data from one of these nights (2 July) are illustrated in Fig. 1. Data from other nights are then of variable quality, from quite good to marginal. A typical example (23 July) is shown in Fig. 2. From approx. 17.00 L.M.T. (L.M.T. = U.T.+4h 12min)to23.00L.M.T.gooddata are recorded. Thereafter, contamination from aurora1 emissions is apparent and the values for the relative intensities of the P,(2) and P,(4) lines and the rotational temperature can no longer be regarded as meaningful. In the early part of the evening (17.00 L.M.T. to 23.00 L.M.T.) the relative intensities of the P,(2) and P,(4) lines vary quite dramatically between 3 and 12 units (intensity is measured in arbitrary units). The
926
L. C.
STUBBS
et al.
; 160 g 140 E 120 If 100
6
P(2)
Day
163
7 6 PI41 5
1600
2000 Local
2200 Mean
2400
0200
0400
0600
0600
Time
FI~.~.DATAFORONENIGHT(~JULY)ON~ICHTHEREWASVIRTUALLYNOAURORALACTIVITYASINDICA~DBY THERELATIVELYLOWANDCONSTANTBACKGROUNDINTENSITY. The relative intensity of the P,(2) and P,(4) lines is shown as well as the rotational temperature calculated
from
the ratio of the intensity of the two lines.
correlation (the value rotational a mean of
between the two OH lines is extremely good of the correlation coefficient is 0.98). The temperature remains fairly steady and yields 184.1 K with a S.D. of 6.4 K.
Seasonal and diurnal variations The mean temperatures for the nights from 4 June to 1 September 1979 on which rotational temperatures could be accurately measured are listed in Tables 2 and 3. The correlation coefficient between the relative intensities of the P,(2) and P,(4) lines is given for each night. The variation of the rotational temperature over the 3 months is shown in Fig. 3. Some authors have reported a maximum in the rotational temperature in winter (see the discussion by Wallace (1962)), whilst others have observed no seasonal variation (for example, Kvifte (1967)). Over the observational period of 3 months, a trend such as a maximum in the rotational temperature near the middle of winter should be detectable if it be there. None is discernible in the data reported here. To further examine whether any diurnal trends existed, hourly mean values of rotational temperature
and the number of points they are based upon are plottedinFig.4for thefirstandsecond halfofthewinter season. The results of this analysis are tabulated in Table 4. The decline near 02.00 L.M.T. in the number of points upon which the mean temperature is based is due to this being the time of maximum frequency of occurrence of aurorae. The only trend observed among the individual nights as illustrated in Figs. 1 and 2 was a gradual steady decrease in the rotational temperature during the course of the evening. The averaged data for 4 June-16 July show no apparent trend, whilst those for 17 July-l September exhibit a gradual steady decrease during the course of the evening. Some authors report a minimum near local midnight (for example, Shefov (1971)) whilst others observe no such trend. The gradual steady decrease in the rotational temperature during the course of the evening is the only trend apparent in the data recorded at Mawson. This trend is in agreement with that reported by Takahashi et al. (1974) at 23” S in Brazil. The data were also analysed into temperature intervals of 10 K to examine the distribution of the rotational temperature. Figure 5 shows the resultant
Measurement
of the OH rotational
temperature
at Mawson,
921
East Antarctica
220 y
200 160
%
160
p
r-w--
Day 204 /
Rejected
Data----~
I!
12
6 I
ii’ 2
LocalMearTlma
F1c.2.
DATA AS FORFIG. 1 BUT FOR 23 JULY,• N WHICH NIGHT AURORAL ACTIVITY COMPLETELY OISRUPTED MEASUREMENTS ATAPPROX. 23.20 L.M.T.
I
I
I
I zoo-
Mean TernperatureK 190-
f
Iso 140-
of
Number
0
I
I
I
Jlne
t
11
1
I
”
July
PoiVs
”
1’
I
’
1”
rl
hm
F1c.3. MEAN NIGHTLYROTATIONALTEMPERATIJREFORTHEPERIOD~JUNE-1 The number oftemperature measurements from which each mean is derived
SEPTEMBER.
is also plotted.
L. C.
928
STUBBS
et al.
TABLE2. MEAN NIGHTLYTEMPERATURES FORTHEPERIOD 4 JUNETO 16 JULY. The correlation coefficient between the intensities of the P,(2) and P,(4) lines is given in the last column
Date
Mean temperature (K)
Standard deviation (K)
Number of points
Correlation coefficient
June
4 5 6 9 14 21 22 23 24 25 26 27 28 29 30
168.5 176.4 177.0 173.5 136.1 185.0 166.6 184.4 183.2 181.1 173.9 170.2 158.6 145.5 140.9
7.3 24.5 10.2 10.2 10.0 14.7 8.6 9.9 9.9 10.6 8.9 11.1 13.0 12.7 11.0
65 109 25 45 54 65 31 81 71 91 26 115 78 82 84
0.97 0.48 0.68 0.73 0.91 0.90 0.86 0.95 0.96 0.92 0.95 0.29 0.85 0.77 0.93
July
1 2 11 12 14 15 16
140.2 139.8 183.0 170.3 170.7 154.2 156.1
9.5 8.1 13.6 9.8 9.1 11.6 14.6
107 132 60 32 47 27 67
0.94 0.97 0.81 0.74 0.92 0.78 0.84
Meon TemperatureK
4tbAne-t6ttlJuty
17thJuly-M saptamts3r
FIG. 4. HOURLYMEANS OFTHEMEASURU) ROTATIONAL TEMPERATURE OVERTHETWO PERIODS 4 JUNE-16JULY AND 17 JULY-~ SEP~MBER. The number of measurements from which each mean is derived is also plotted. The time is given in L.M.T.
Measurement
of the OH rotational
temperature
at Mawson,
East Antarctica
929
TABLE 3. MEAN NIGHTLY TEMPERATURES FOR THE PERIOD 17 JULY-~ SEPTEMBER. The correlation coefficient between the intensities of the P,(2) and P,(4) lines is given in the last column
Mean temperature (K)
Date July
August
September
17 18 21 22 23 24 2.5 26 27 28 30 31 2 4 9 11 13 14 15 16 20 21 22 23 24 25 26 27 28 30 31 1
Standard deviation
184.3 156.0 190.2 158.2 184.1 199.8 170.0 154.8 164.2 152.1 175.1 176.2 168.5 160.5 191.4 186.8 165.7 161.0 169.1 159.1 165.1 158.5 155.3 168.1 160.1 166.3 168.9 168.9 163.1 169.1 171.0 162.8
for the periods 4 June-16 July and 17 July1 September. For example, in the period 17 July-l September 26.0% of the temperature values lie in the range 16&l 70 K. The median value for each period lies in the range 16&170 K as does that for all data combined. The data for the period 4 June-16 July show peaks in the distribution near 140 and 180 K. This double peak appears to reflect variations in mean temperature from night to night over that period. distribution
Possible evidence for aurora1 heating
There is generally little evidence for any increase in rotational temperature caused by aurora1 activity. Data from one night (25 June) are shown in Fig. 6. In the period before the aurora1 display, there is a noticeable steady decrease in the values of the rotational temperature, as discussed above, and likewise after the aurora1 display the temperatures
Number Of
points
(K) 14.7 15.2 11.3 12.9 6.4 11.4 14.2 13.7 8.3 16.1 16.5 14.7 13.5 9.3 15.1 7.1 9.7 5.7 8.5 8.7 9.3 10.3 8.8 12.3 10.2 3.0 10.4 6.5 16.5 9.7 11.5 8.9
25 59 89 95 48 45 109 46 40 80 62 81 51 20 62 56 45 70 44 92 22 22 60 100 41 12 50 27 56 86 66 42
Correlation coefficient 0.90 0.85 0.92 0.94 0.98 0.89 0.81 0.97 0.81 0.93 0.94 0.78 0.89 0.83 0.64 0.80 0.76 0.90 0.66 0.90 0.82 0.89 0.90 0.96 0.87 0.87 0.46 0.94 0.89 0.91 0.78 0.90
display the same gradual decrease. However, there is a marked increase of approx. 30 K after the aurora1 activity. Whilst possibly indicative of aurora1 heating, the evidence provided by this single event is hardly conclusive. For instance, this result can be compared with data obtained the following evening. A more intense aurora1 display occurred over Mawson from 23.45 L.M.T. to 03.45 L.M.T. In the period before and after this display, meaningful OH measurements could only be made from 17.40 L.M.T. to 18.52 L.M.T. and from 04.59 L.M.T. to 07.07 L.M.T. respectively. The mean of the eleven points in the period before the aurora1 display is T = 169.6 K with e = 6.7 K. For the fifteen points in the interval after the aurora1 display, the mean temperature is T = 177.1 K with c = 9.2 K. This is either indicative of no aurora1 heating, or else that there was heating prior to twilight before OH measurements commenced.
L. C. STCJBBS et al.
930
TABLE4. HOURLYMEANSFORTHEROTATIONAL TEMPERATURES MEASURED FROM4 JUNETO 16 JULYAND 17 JULYTO 1 SEPTEMBER.
Time intervals are at L.M.T. 4 June-16 JULY
Time interval (L.M.T.)
Mean temperature
Standard deviation
(K)
(K)
165.1 159.7 169.6 168.1 165.9 163.8 159.0 159.0 165.6 162.4 155.6 152.8 167.0 161.4 163.0 168.4 161.6 143.7
31.3 19.7 17.2 17.7 19.9 20.4 20.0 22.5 21.3 18.0 22.4 24.3 25.5 22.5 17.4 23.2 25.4 29.5
1X&1600 1600-1700 17W1800 18OG1900 190&2000 2OOG2100 210@2200 2200-2300 2300-2400 24WOlOO 01OcO200 020@0300 030&0400 040&0500 05WO600 060@0700 07OGO800 08KW900
Number of points 8 95 148 1.56 151 141 128 115 87 72 50 39 47 58 65 71 49 14
(a)
90
110
130
150
Rotational
90
II0
I30
I50
Rotational
170
190
temperature
170
190
temperature
210
230
K
210
K
17 July-l September
._
230
_
Mean temperature
Standard deviation
(K)
(K)
Number of points
171.8 173.4 169.3 173.6 174.0 171.1 166.2 164.5 163.0 162.7 164.4 164.4 165.0 164.2 171.0 166.5
9.1 15.6 17.3 16.0 18.9 16.5 17.7 20.1 16.7 20.8 18.6 16.1 13.3 16.1 19.9 19.8
13 119 206 200 200 158 139 133 108 73 98 99 113 121 83 26
Latitudinal considerations The study of OH airgiow emissions has mainly been confined to the Northern Hemisphere. Kvifte (1967) gave an extensive list of reports of measurements of the OH rotational temperature and all but two were in the latitudinal range of40-85” N. The noticeable difference to the results reported here is that, in general, the Northern Hemisphere rotational temperature values were much higher than those at Mawson. Most of the values of Kvifte’s list lie in the 21&250 K range. One exception is Noxon (1964) who studied the latitudinal dependence of the OH rotational temperature using a spectrometer installed in ajet aircraft. He reported 215, 170 and 160 K for the latitudinal ranges 62-69” N, 6977” N and 77-85” N respectively. The latter two values are similar to the values measured at Mawson. In the Southern Hemisphere there is little data for comparison. Armstrong (1975) reported values for the rotational temperature in the range 220-310 K in Australia (30” S) ; Blackwell et al. (1960) reported 293 K in Bolivia (16” S); and Takahashi and co-workers (Takahashi et al., 1974, 1979; Clemesha et al., 1979) reported values in the range 16&l 90 Kin Brazil (23” S).
FIG. 5. FREQUENCY OF OCCURRENCE0~ TEMPERATURE MEASUREMENTS IN 10 K INTERVALS OVERTHEPERIOD (a) 4 JUNE16 JULY; AND (b) 17 JULYA SEPTEMBER. The total number of points in period (a) is 1494 and in period
(b) is 1803.
Measurement
of the OH rotational
temperature
at Mawson,
Bat
East Antarctica
931
Day 176
IO-9-8--
7--
r Rejected
Data - - - -1
I
6-1
5-4-P(2) 3--
P(4)
2-I--
I
I400
1
I 1600
I
I 1800
1
I
I
2000
1
2200
I
twcl
I
2400
02c0
I
I 0400
I
I 0600
I
I 0600
Local ~Tinm Ftc.6. TEMPERATUREDATAFORONENIGHT MEASUREMENTSFORA
(25 JUNE)ONWHICHAURORALACTIVITYINTERRUPTEDTEMPERATURE PERK," OFAPPROX. 4 h, AFTER WHICH THETEMPERATUREMEASUREMENTRESUMED HIGHERVALUETHANBEFOKETHEDISTURBANCE.
The range of values measured in Brazil is in line with that measured at Mawson. Given the small number of measurements that have been made of the rotational temperature in the Southern Hemisphere, no conclusion can be drawn concerning any systematic latitudinal dependence of rotational temperatures.
CONCLUSION
The average rotational temperature for the OH (8,3) band emission observed at 67” S at Mawson, East Antarctica, during the winter of 1979 lies in the range 16&170 K. A multi-channel photometer was employed whereby a sampling rate for the rotational temperature of eight measurements per hour was possible. One event indicative of aurora1 heating was observed, but a
AT A
single observation must be regarded as inconclusive. The maximum in the rotational temperature in winter frequently observed in seasonal variation studies is not observed. The only diurnal trend observed is a gradual decrease in the value of the rotational temperature throughout the course of the evening. The small number of Southern Hemisphere measurements precludes comment at this stage on the latitudinal variation of the OH rotational temperature in the Southern Hemisphere. Acknowledgements~-The assistance of the members of the Mawson wintering party is gratefully acknowledged, in particular, A. Blake, P. Delaney, P. Magill, B. Vince and J. Wignall as well as N. Voloshinov, exchange scientist from the Soviet Antarctic Expedition. The authors are also grateful for assistance with the data processing provided by H. Burton (Antarctic Division) and the Bureau of Meteorology.
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