Northern Hemisphere stratospheric summer from MIPAS observations

Abstract

AbstractData from the MIPAS instrument on Envisat, supplemented by meteorological analyses from ECMWF and the Met Office, are used to study the meteorological and trace‐gas evolution of the stratosphere in the Northern Hemisphere during spring and summer 2003. A Pole‐centred approach, together with sequences of vertical profiles along the viewing tracks of the MIPAS instrument, is used to interpret the data in the physically meaningful context of the evolving summertime high. During April the vortex break‐up and build‐up of the summertime high gives rise, in the mid‐stratosphere, to a ‘frozen‐in’ anticyclone (FrIAC), over the Pole, encircled by vortex fragments at ∼50°N. As the summer moves on, the FrIACs and vortex fragments are gradually smoothed out but they persist in the mid‐ and upper stratosphere until July–August as roughly zonally symmetric W‐shaped tracer isopleths. The persistence of the W shows the slowness of isentropic mixing processes at these levels during the summer. As the summertime high becomes dominant during June–August, net photochemical ozone loss produces a low ozone pool in the lower and mid‐stratosphere. Finally, as the summertime high decays and the wintertime polar vortex builds up from September onward, the low ozone pool extends vertically throughout the stratosphere, and the tracer isopleths at high latitudes start to dip, showing the effects of wintertime diabatic descent. Of these features, to our knowledge, the W‐shaped tracer isopleths have not been observed previously. Copyright © 2007 Royal Meteorological Society