Relation between ozone and temperature in the Arctic stratosphere

Yu. Yu. Kulikov and V. G. Ryskin

Institute of Applied Physics, Nizhny Novgorod, Russia

Contents

Abstract

1. Introduction

Interest in the relation between temperature and ozone fields in the terrestrial atmosphere is understandable. It is known that the main stratospheric heating occurs as a result of solar ultraviolet radiation absorption by the ozone molecules. Therefore ozone concentration changes cause changes in the temperature regime of this region. On the other hand, any thermal disturbance influences the rates of the ozone formation and destruction reactions. According to Brasseur and Solomon [1984], this interaction mechanism has a negative correlation between the temperature and ozone content. Both of these interinfluence effects act in the atmosphere under various types of transport. For example, Randell [1993] noted that under planetary wave propagation a thermal disturbance arises which is in antiphase with ozone content changes in the upper stratosphere and in phase with the ozone content changes in the lower stratosphere. However, the role of chemical, temperature, and dynamical mechanisms in the total process of the ozone and temperature interaction has not been sufficiently studied.

The analysis results of multiyear satellite measurements of ozone variations presented by Finger et al. [1995] also indicate the existence of positive and negative correlations between ozone content and temperature in the lower stratosphere (the 30-mbar level) and at the 1.0- to 2.0-mbar level, respectively. However, it should be emphasized that these satellite data obtained by the backscatter ultraviolet spectrometer bear no information on the ozone content at polar latitudes of the winter hemisphere. Therefore study of the relation between ozone and temperature during polar night conditions, when photochemical processes in the stratosphere are weakened and dynamics might play a governing role, becomes important.

2. Experimental Data

The results of both the microwave measurements of the stratospheric ozone above 20 km and rocket and radiosonde measurements of temperature and pressure vertical profiles at Heiss Island (Franz-Josef Land, 80^o N, 58^o E) during the polar night (October-December 1988) and during a major stratospheric warming (February-March 1989) are presented in this paper. This study was carried out in the scope of a coordinated experiment on the study of ozone layer structure and dynamics at polar latitudes of the northern hemisphere and was organized by the Central Aerological Observatory (Dolgoprudny, Moscow Region). Ozone behavior in the middle and upper stratosphere was investigated with the help of a ground-based microwave spectrometer [Borisov et al., 1989], the receiver of which was adjusted to the resonance frequency of the 4_0.4-4_1.3 ozone rotational transition (n₀ = 101,736.76 MHz) in the ground vibrational state. The uncooled receiver had a noise temperature of about 5000 K under a one-band reception regime. The spectra analyzer was a filter system (20 spectral channels with a passband of 3 MHz each) with a variable step of channel frequency adjustment and a total analysis band of 102 MHz. The method of measurements described by Borisov et al. [1989] made it possible to obtain ozone atmospheric line emission spectra, which were then used to calculate the N_O3(z) ozone vertical distribution in the altitude region 22-52 km.

The procedure of N_O3(z) profile restoration included adjustment of the magnitude and shape of the ozone spectral line (the calculated spectrum) to the initial experimental spectrum by the method of variations of parameters of the N_O3(z) analytical dependence. This method of evaluation of the ozone vertical distribution is fairly simple and has been used by some scientists to solve similar reverse problems (see, for example, De La Noe et al. [1983]). In the process of restoration, the parameters were adjusted to reach the minimum difference between the ozone line calculated spectrum (solution of the direct problem) and the experimental spectrum within the limits of its radiometer measurement errors. In the restoration procedure, we used the real temperature and pressure dependencies on altitude and that made it possible to reduce significantly uncertainties in the O ₃ vertical profiles obtained. As a result the error of vertical ozone distribution determination (altitude region of 22-52 km) from its measured spectra did not exceed 20%. It has already been mentioned above that the vertical profiles of temperature and pressure were obtained from the data of rocket and aerological sounding. Radiosondes were flown thrice a day and provided information on pressure and temperature up to 25-30 km. Rockets were launched once a week (sometimes more often) and measured atmospheric parameters at altitudes from 25 to 70 km. Besides these measurements, in February-March 1989 a study of the ozone layer was carried out by the American and German balloon electrochemical sondes ECC-4A (Wyoming University, United States) and OSE-3 (Aerological Observatory, Lindenberg, Germany). Moreover, rockets with the chemiluminescent ozonosondes (4 launches) and optical ozonometers (4 launches) were launched [Rosen et al., 1992]. The total ozone content was also measured by the Breuwer spectrophotometer 45 (direct radiation from the Moon).

Figure 1 shows the results of measurement of the ozone concentration and temperature in the stratosphere. Note that the measured stratospheric temperatures at levels of 25, 35, and 45 km (solid circles in Figure 1) were obtained with a weekly interval and the ozone concentrations (daily mean) are shown much more frequently, once a day to be exact (solid line in Figure 1). To obtain daily vertical profiles of O ₃ between rocket launches, we used the linear interpolation of the pressure and temperature altitude distribution (above 25 km). Below 25 km, the data on these atmospheric parameters were available every day (thrice-a-day aerological sounding).

3. Results and Discussion

During October-December 1988, Heiss Island was situated within the circumpolar vortex. One can see that in the lower stratosphere (25 km) there was a seasonal temperature decrease, which corresponded to the mean zonal behavior for 80^o N (see, for example, Barnett and Corney [1985]). The fact that the temperature at a height of 25 km in November was below the mean value attracts attention. In the same time, a gradual increase of ozone concentration was observed at this level. Actually, a seasonal anticorrelation between temperature and ozone with a coefficient of -0.44 was registered in the lower stratosphere in polar night conditions. However, if one excludes the autumn-winter trend of the temperature and ozone concentration, the short-term variations (on a scale of 7 days) of these values become in phase with the fairly high positive correlation coefficient of +0.67. Finger et al. [1995] and Randell [1993] obtained approximately the same correlation coefficient for middle latitudes. Using the linear regression method, we then obtained the relation coefficient between variations of the ozone concentration and temperature which is (0.033 0.004) ppmv K ^-1 for the 25-km level. Randell [1993] give for this coefficient the value of (0.055 0.018) ppmv K ^-1 at equatorial latitudes and the 30-mbar level.

The seasonal temperature changes are negligible (within several degrees) in the middle and upper stratosphere (altitudes of 35 km and 45 km). In these conditions (see Figure 1) the positive correlation between ozone and temperature is evident, the correlation coefficient being +0.43 and +0.21 for 35 km and 45 km, respectively. We assume that the positive correlation is really higher; however, insufficient frequency of temperature detection made it impossible to confirm this assumption. Nevertheless, our results do not contradict the statement that ozone and temperature change in phase in the lower stratosphere, where dynamic factors predominate. The character of this relation in the middle and upper stratosphere is opposite to the relation derived earlier [Finger et al., 1995; Randell, 1993]. However, it should be reminded once more that our results were obtained during late polar night, when the photochemical mechanism of ozone formation and destruction is considerably weakened and transport processes begin to play an important role even in the so-called photochemical region. It is worth noting that during October-December the satellite data on total ozone content in the nonsunlit regions poleward from the polar circle are absent because of their specifics. Such data would have been very useful for a comparison with the microwave measurements of the stratospheric ozone above 20 km. Integrating our data, we obtained that the ozone content in the atmosphere above 20 km in this period was extremely low (about 50 Dobson units (DU)).

Circumpolar vortex destruction began at the end of January; in the beginning of February 1989 and on February 18 the vortex was split in two parts [Rosen et al., 1992]. As a result, Heiss Island appeared outside the vortex boundaries. The destruction was accompanied by a major stratospheric warming, and as a result on February 20 there was an excess (of 50 K and 20 K at 25 km and 35 km, respectively) above the mean zonal temperatures (see Figure 2). The "heat" came down from the stratopause level ( 50 km) to the lower stratosphere. A considerable (from 2 to 4 times) increase in the O ₃ concentration as compared with undisturbed values was registered in this period. The largest amplitude of the O ₃ concentration changes (by 4 times) as compared with the "quiet" period (October-December 1988) was observed at an altitude of 25 km. At altitudes of the ozone layer maximum (15-17 km), similar changes (according to balloon sounding data) reached only 100%. The subsequent stratospheric cooling led to a decrease of the ozone content at all levels, the stratosphere staying isothermal during several days. It should be noted that the ozone concentration changes were in phase with the temperature changes everywhere in the stratosphere. However, at an altitude of 25 km, the correlation coefficient was considerably higher (+0.84), whereas at 35 km and 45 km it was +0.3 and +0.25, respectively. A high degree of correlation during the stratospheric warming was detected in other measurements. For example, the total ozone content measured by the Breuwer spectrophotometer increased from 354 DU on February 13 to 532 DU on February 19. The following ozone concentration changes were registered by the ECC-4A electrochemical sensors at an altitude of 25 km: on the average, 2.4 10¹² cm ^-3 in January, 3.3 10¹² cm ^-3 on February 15, 6.3 10¹² cm ^-3 on February 19, 6.6 10¹² cm ^-3 on February 23, and 3.7 10¹² cm ^-3 on March 2.

A similar picture was also observed on these days at other Arctic stations [Kyro et al., 1992; Neuber and Kruger, 1990; Rabbe and Larsen, 1992]. The positive correlation between the temperature and ozone content was observed elsewhere in the lower stratosphere, where the processes are controlled by dynamics. It is worth noting that the warming occurred when the stratosphere was sunlit. Nevertheless, it seems that due to strong vertical heat transport, which was mentioned above, the change of the stratospheric ozone content occurred during this time mainly because of dynamic process. In particular, the temporal delay in changes of the ozone concentration at various altitude levels (see Figure 2) indicate that. The ozone increase began in the upper stratosphere, and then the increase occurred in the lower stratosphere several days later. This phenomenon is a possible manifestation of vertical motion in the atmosphere.

4. Conclusions

Concluding, we emphasize the main results which were obtained with the help of microwave measurements of the stratospheric ozone and simultaneous temperature and pressure in situ measurements in the Arctic:

1. The seasonal negative correlation between ozone and temperature in the lower stratosphere and the positive correlation in the middle and upper stratosphere were registered during polar night.

2. Positive correlation between ozone and temperature at all stratospheric levels was detected during a major stratospheric warming (February-March 1989).

Acknowledgments

References

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