Seasonal Climatology: Vertical-Meridional Distribution of Zonal Wind
Analysis and Codes by Sandro Lubis
Graduate Student of Leipzig Institute for Meteorology, University of Leipzig, Germany
All computations are made using
[ NCAR Command Language (NCL)]
The seasonal zonal wind has been computed using pressure coordinates from the ERA-Interim dataset 1989 – 2007. Common features of zonal-mean zonal wind in the atmosphere are depicted by strong wind in the subtropical atmosphere near 30N/S, westerly with speed of around 30 m/s and at height of 200 hPa (roughly 10-12 km). The so called sutropical jets are strongly observed in the winter hemispher [DJF for NH] and JJA for SH. Meanwhile the weaker jet are always indicated in summer hemisphere with speed of less than 24 m/s, near 45N/S. The typical jets in the NH is stronger than in SH.
The easterly winds are located in the low level of low latitudes between 30S/N (In tropical belts). These lower level easterlies are also called as trade winds. One intersting here, in winter hemisphere, the westerlies are strong extending until upper stratosphere while in opposite hemisphere the westerlies weaker [easterlies dominant above 200hPa] resulted by the coriolis torque effects and the momentum transfer from the the existence of planetary waves, in this context is Rossby wave.
Figure 1. Meridional cross-section of zonal mean zonal wind (m/s) under annual mean condition.
Figure 2. Meridional cross-section of zonal mean zonal wind (m/s) under DJF (Winter). MAM (Spring), JJA (Summer) and SON (Autumn) mean condition.
[computed by Sandro, data was obtained from the course of Global Climate Dynamic, Leipzig Institute for Meteorology, Germany]