The effects of atmospheric waves on the amounts of polar stratospheric clouds

Abstract

Abstract.A quantitative analysis on the relationship between atmospheric waves and polar stratospheric clouds (PSCs) in the 2008 austral winter and the 2007/2008 boreal winter is made using CALIPSO, COSMIC and Aura MLS observation data and reanalysis data. A longitude-time section of the frequency of PSC occurrence in the Southern Hemisphere indicates that PSC frequency is not regionally uniform and that high PSC frequency regions propagate eastward at different speeds from the background zonal wind. These features suggest a significant influence of atmospheric waves on PSC behavior. Next, three temperature thresholds for PSC existence are calculated using HNO 3 and H 2 O mixing ratios. Among the three, the T STS (a threshold for super cooled ternary solution)-based estimates of PSC frequency accord best with the observations in terms of the amount, spatial and temporal variation, in particular, for the latitude ranges of 55 • S-70 • S and 55 • N-85 • N. Moreover, the effects of planetary waves, synoptic-scale waves and gravity waves on PSC areal extent are separately examined using the T STS -based PSC estimates. The latitude range of 55 • S-70 • S is analyzed because the T STS -based estimates are not consistent with observations at higher latitudes (<75 • S) above 18 km, and PSCs in lower latitudes are more important to the ozone depletion because of the earlier arrival of solar radiation in spring. It is shown that nearly 100 % of PSCs between 55 • S and 70 • S at altitudes of 16-24 km are formed by temperature modulation, which is influenced by planetary waves during winter. Although the effects of synopticscale waves on PSCs are limited, around an altitude of 12 km more than 60 % of the total PSC areal extent is formed by synoptic-scale waves. The effects of gravity waves on PSC areal extent are not large in the latitude range of 55 • S-70 • S. However, at higher latitudes, gravity waves act to increase

A decadal satellite record of gravity wave activity in the lower stratosphere to study polar stratospheric cloud formation

“…This first survey suggests that formation events appear more frequently in the Southern Hemisphere than in the Northern Hemisphere. This is not consistent with studies showing that there are larger proportions of PSCs due to orographic gravity waves in the Arctic than in the Antarctic (Kohma and Sato, 2011;. However, our findings might be biased due to the more stable atmospheric conditions in the Southern Hemisphere, which ease the identifica- Figure 13.…”

“…Previous studies on PSC formation used mesoscale model output (Höpfner et al, 2006a;Noel and Pitts, 2012;Orr et al, 2015) or global positioning system radio occultation observations (Kohma and Sato, 2011;Alexander et al, 2011 as a source of information on gravity waves. The use of Atmospheric Infrared Sounder (AIRS) observations for that purpose was first explored by Eckermann et al (2009) and Lambert et al (2012).…”

Simultaneous occurrence of polar stratospheric clouds and upper-tropospheric clouds caused by blocking anticyclones in the Southern Hemisphere

“…Previous studies indicate that PSCs are sometimes observed in association with anticyclonic PV anomalies near the tropopause (Teitelbaum et al, 2001;Kohma and Sato, 2011). Figure 6 shows the probability of the simultaneous occurrence of PSCs and UCs at 70-75 • S in June through September of 2007-2011 as a function of PV anomalies from the zonal mean of 300 K (∼ 8 km) and 550 K (∼ 23 km) isentropic surfaces.…”

“…Dörnbrank and Leutbecher (2001) showed that temperatures low enough to enable the formation of ice PSCs are controlled by mesoscale temperature fluctuations due to mountain waves in the Arctic, while NAT formation is significantly controlled by the synopticscale temperature fluctuations. Kohma and Sato (2011) quantified the contribution of each type of waves to the areal extent of PSCs in both hemispheres using a temperature threshold based on temperatures from reanalysis data and GPS radio occultation observations and mixing ratios of HNO 3 and H 2 O from microwave limb sounder observations. They showed that planetary-scale temperature perturbations have a great contribution to areal extent of PSCs in the latitude range of 55-70 • S while the contribution of synoptic-scale perturbation is large only around an altitude of 12 km.…”

“…PSCs are strongly modulated by atmospheric waves such as planetary, synoptic-scale and gravity waves (Teitelbaum et al, 2001;Carslaw et al, 1999;Dörnbrack and Leutbecher, 2001;Eckermann et al, 2009;McDonald et al, 2009;Alexander et al, 2011;Kohma and Sato, 2011). Teitelbaum et al (2001) showed that PSCs and synoptic-scale ozone minima appear simultaneously with synoptic-scale…”