Gravity wave seasonal variations and their influences on polar mesospheric clouds in Antarctica

Details Gravity wave seasonal variations and their influences on polar mesospheric clouds in Antarctica Gravity wave seasonal variations and their influences on polar mesospheric clouds in Antarctica

May 2007

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2007agusmsa53a..05y&link_type=abstract

American Geophysical Union, Spring Meeting 2007, abstract #SA53A-05

Other

3311 Clouds And Aerosols, 3334 Middle Atmosphere Dynamics (0341, 0342), 3360 Remote Sensing

Scientific paper

Gravity waves (GWs) play an important role in the dynamics of global middle and upper atmosphere. Quantitatively characterizing GW in the upper stratosphere and mesosphere are still rare in Antarctica. In this paper we present a study of GWs using the lidar data obtained at South Pole (90°S) from December 1999 to January 2001 and at Rothera (67.5°S, 68.0°W) from December 2002 to March 2005 with the University of Illinois Fe Boltzmann/Rayleigh lidar. The root-mean-square (RMS) relative density perturbation in 30- 45 km derived from the Rayleigh lidar data is used to characterize the stratospheric GW strength. The obtained GW characteristics include vertical wavelength of 2-10 km, vertical phase velocity of 2-6 km/h, and the period of 0.5-3.5 hours at both Rothera and South Pole. Seasonal variations of GW strength at Rothera are observed to be larger than those at the South Pole. Averaged RMS relative density perturbation at Rothera is 1.19+/-0.38 in winter and 0.46+/-0.24 in summer, while averaged RMS relative density perturbation at South Pole is 0.81+/-0.22 in winter and 0.40+/-0.25 in summer. The observed larger difference in winter but nearly no difference in summer in the GW strength between Rothera and South Pole may be explained by the GW source difference and wind filtering effect. Topography of Rothera and South Pole is very different - featureless area at South Pole but mountain and coast area near Rothera. Thus, GW sources are expected to be stronger at Rothera than at South Pole, which results in larger stratospheric GW strength at Rothera than at the South Pole in winter, when wind filtering effect is very weak. However, due to the strong wind filtering effect in summer, the GWs that can reach stratosphere are similar at these two sites. It has been suggested that GW may influence the formation or occurrence of polar mesospheric clouds (PMC). An initial study using Rayleigh lidar at Sondrestrom (67.0°N, 50.9°W) indicates that the strengths of GW and PMC are negatively correlated. However, such a correlation has not been examined in Antarctica until now. The total backscatter coefficients (TBC) measured by the Fe lidar are used to represent PMC brightness in the mesopause region. We investigate the correlation between daily (instead of hourly) averaged TBC and RMS density perturbation. The derived linear correlation coefficient (LCC) is -0.37 with confidence level of 92% at Rothera and -0.09 with confidence level of 40% at South Pole. Although the obtained LCC is not statistically significant (confidence level higher than 95% is considered as significant), our data indicate a negative correlation between GW and PMC at Rothera. The data also indicate that there is no correlation between GW and PMC at the South Pole. This may be explained by the large temperature difference between Rothera and South Pole in summer mesopause region. As the Rothera temperature is close to the PMC formation threshold (~150 K) the temperature perturbation induced by GW can significantly alter the PMC formation or disappearance. Meanwhile, the temperature perturbation induced by GW may not drive the South Pole temperature above the threshold, thus, PMC brightness is not affected much.

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