Skewness, Kurtosis and Extreme Values of Northern Hemisphere Geopotential Heights

Abstract

Twelve summers and 11 winters of Northern Hemisphere 500 and 1000 mb geopotential height are used to calculate the third and fourth moments of height in the nondimensional form of skewness and kurtosis. Geopotential height exhibits small but statistically significant departures from a normal distribution in places, especially in low latitudes. Negative skewness and high kurtosis occurs south of the mean jet streams at 500 mb and over the low latitude oceans at 100 mb, while positive skewness appears in high latitudes at 500 mb near the mean troughs. Kurtosis significantly less than that of a normal distribution appears at 500 mb over the midlatitude oceans where large variance of geopotential height and frequent blocking are observed. At 500 mb skewness and kurtosis appear closely related to the extreme values of geopotential height. Both 500 and 1000 mb surfaces have high maximum values over the eastern portions of the means in regions of blocking.