A study of modulation of polar stratospheric clouds by atmospheric waves in the Southern Hemisphere using CALIPSO lidar data

Polar stratospheric clouds (PSCs) are the clouds that appear in the cold lower stratosphere in polar regions and play a key role in the destruction of polar stratospheric ozone. Atmospheric waves including planetary, synoptic-scale and gravity waves modulate temperature fields and hence affect the PSC amounts as shown by previous studies. Thus, for better understanding of stratospheric ozone destruction, a comprehensive and quantitative analysis was made in this study on the relationship between atmospheric waves and PSCs. We used the PSC data from satellite lidar observations (CALIPSO), H2O and HNO3 data from a satellite microwave limb sounder (Aura MLS), reanalysis data (ERA Interim) and high-resolution dry temperature data from GPS radio occultation observations (COSMIC). The analysis was focused on the Southern Hemisphere. The frequency of PSC occurrence at each location and time, hereafter referred to as the PSC frequency, was calculated as a proxy of the PSC amount from CALIPSO data (VFM data, showing the presence of cloud at observation points). The polar-stereo map shows that the PSC frequency is not regionally uniform, and suggests influence of the atmospheric waves. It is seen in the longitude-time section that high PSC frequency regions propagate eastward, which accords well with the movement of negative temperature anomaly from the zonal mean. First the effects of planetary waves in the stratosphere and synoptic-scale waves in the upper troposphere are analyzed using potential vorticity (PV) on the isentropic surfaces of 650 K (a height of about 20 km) and 300 K (about 9 km) respectively. It is shown that low (cyclonic) PV anomaly is frequently associated with high PSC frequency at 650K, while high (anti-cyclonic) PV anomaly is sometimes accompanied with high PSC frequency. The low PV anomaly in the stratosphere generally has long vertical scales and is associated with low temperature, while the high PV anomaly in the upper troposphere has very short vertical scales and hence negative temperature anomaly is formed in the lower stratosphere. The eastward propagation of PSC frequency observed in the longitude-time section is frequently followed by these low PV anomaly in the stratosphere and occasionally by high PV anomaly in the upper troposphere. To estimate the net effect of the planetary waves on the PSC quantitatively, we compared two “PSC area” with and without planetary wave effects. The former is calculated as the area where the temperature is below the TNAT based on unfiltered H2O and HNO3 data, and the latter is calculated using temperature, H2O and HNO3 data from which the zonal wavenumber 1-3 components were extracted. It was shown that the PSC area is increased by about 10% by planetary waves on average. Similar analysis was made on the PSC area excluding synoptic-scale wave effects. However, meaningful results were not obtained. Next, to examine the gravity wave effects on the PSC, we used GPS temperature data. The gravity wave potential energy is usually higher near the Antarctic Peninsula than in the other regions in June through September. However, the PSC frequency around the Antarctic Peninsula is higher than the other regions only in June and September, while the difference is small in July and August.