Previous: Ext. Abst. Next:The Arctic Vortex Up: Ext. Abst.

Introduction

As part of the EU project Polar Vortex Change (PVC, coordinated by Esko Kyrö, FMI) NILU has acquired the 15-year ECMWF re-analysis set, the so-called ERA-15 data set. ERA-15 covers the period from 1 Jan. 1979 to 28 Feb. 1994. The data are global in coverage and in spectral form at T₁₀₆ resolution. Converted to a latitude/longitude grid the resolution is 1.125° X 1.125°. The 32 levels reach from the ground to 10 hPa. In addition we have acquired daily global fields at T₁₀₆ resolution from 1994 up to present. The combined data set makes it possible to study the climatology of the polar vortex in a 20-year perspective. In the present study we have looked at the development of various polar vortex parameters from 1979-80 until present. We have limited the study of the Arctic vortex to the four months January through April and to the isentropic level of 475 K (approx. 19 km or 50 hPa). The Antarctic vortex has been studied at several levels from 400 to 550 K and for the months September through December.