Geopotential height annual cycle in Antarctica: Year-to-Year variability and trends, 1980-2004

ADRIAN E. YUCHECHEN; PABLO O. CANZIANI; SUSANA A. BISCHOFF

Perugia, Italia

Congreso; IUGG XXIV General Assembly; 2007

International Union of Geodesy and Geophysics (IUGG)

The purpose of the present work is to detect trends in geopotential height for several mandatory reporting levels of the atmosphere over Antarctica within the period 1980-2004. In doing so, we attempt to analyze data from fifteen rawinsonde stations distributed all over the continent. Unfortunately, only eight stations fulfill the condition that its datasets cover the whole period. These stations are Amundsen-Scott (89009), Halley (89022), Novolazarevskaja (89512), Syowa (89532), Davis (89571), Mirnyj (89592), Casey (89611) and McMurdo (89664). Station 89009 is located in the South Pole, whereas station 89022 is located in Western Antarctica. The rest of the stations are located in Eastern Antarctica. The mandatory levels analyzed are 850, 700, 500, 400, 300, 250, 200, 150 and 100 hPa. Every set of twelve monthly means are year-to-year Fourier analyzed in order to obtain the following parameters for the first two harmonics: V1, V2 and the ratio A2/A1; V1 (V2) denotes the explained variance of the first (second) harmonic and A1 (A2) denotes the amplitude of the first (second) harmonic. Trends are detected by means of a parametric test and using a confidence level of 95%. If a trend is detected at any level, a linear regression is carried out to determine whether the trend is positive or negative. In general, results are as follows. As to V1, the lower levels of the troposphere are negative trended in the coastal region limited by 30W-120E. Regarding V2, negative trends are detected for the stratosphere in Western Antarctica. Concerning A2/A1, positive trends are detected for the lower levels of the troposphere in the coastal region limited by 30W-90E. For the lowest levels of the troposphere in this latter region, seeing that the value of A2/A1 is positive trended whilst the value of V1 possesses a negative trend, the explained variance for the first harmonic decreases favoring harmonics higher than the second, because no trends are detected for V2. Moreover, since V1 can be related to the presence of the polar vortex, it can be concluded from this research that its influence is decreasing in the lower levels of the atmosphere, at least in the coastal region limited by 30W-120E.