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Abstract

One of the generally accepted climatic effects of stratospheric aerosol injection is the reduction of the global radiation in high latitudes by an order of 57. at El Chichon type eruptions . It is suggested that this‘radiation deficit is possible external forcing factor for the above—mentioned climatic anomalies associated with ENSO events. To test this hypothesis, the effect of high—latitude radiational forcing was examined in a GCM experiment. The results provide physically—consistent evidence in support of the basic hypothesis. The main supporting factor is the creation of enhanced snow cover in regions of Asia which are removed from the location of the introduced radiation anomaly. The simulated results show certain features, which are well known from observations in weak monsoon years, i.e. the weakened easterly jet in the upper troposphere over northern India, prolonged winter monsoon conditions and prevailing anticyclonal vorticity anomalies over the entire Indian summer monsoon region. Over the western Pacific at the end of boreal winter (May), increased convective activity leads to a negative Walker Circulation anomaly with westerly wind anomalies near the surface and easterly anomalies in the upper troposphere. This is known as one of the most important anomalies at the beginning of an ENSO event.