Доклади на Българската академия на науките Comptes rendus de l’Acad´ emie bulgare des Sciences Tome 60, No 8, 2007 EXPLORATIONS COSMIQUES COULD WE EXPLAIN THE SOLAR-QBO INFLUENCE ON THE TROPOSPHERE-STRATOSPHERE SYSTEM? Nataliya A. Kilifarska, Plamen J. Mukhtarov (Submitted by Corresponding Member P. Velinov on July 3, 2007 ) Abstract Measurements and models’ results show that solar and QBO signals found in many atmospheric parameters are comprehensively mixed. This makes a separation and explanation of the mechanisms of such an influence extremely difficult. A brief r´ esum´ e of the most known mechanisms, presented here, shows that neither of the existent hypotheses are able to explain the great variety of features and exceptions observed in Solar-QBO interrelations and their effect on the troposphere-stratosphere system. Unlike the traditional pathway for solar signal transition – from the upper stratosphere poleward and downward to the troposphere – we supposed that tropical UTLS region may be “arena” for solar-QBO interactions. The main reason for this is a statistical result reported from many authors that the tropical UTLS is warmer: a) at solar maxima than at solar minima; and b) during west QBO phase than during east one. Moreover, the QBO amplitude is strongest in the lower stratosphere and the experimental evidence for its influence on the atmospheric parameters is remarkable. We recognized four main channels of this coupling: 1) Redistribution of the additional solar heating away from the tropical UTLS through the QBO induced secondary meridional circulation; 2) Feedbackup effect of redirected solar signal on: i) circulation and, ii) planetary wave propagation conditions into the lower stratosphere; 3) Solar control over the wave propagation and Brewer-Dobson circulation in the middle and upper stratosphere; 4) Solar modulation of the QBO duration. Key words: solar-QBO interrelations, explanation Introduction. Quasi-decadal variability found in different atmospheric parame- ters (temperature, geopotential height, winds, chemical compositions, etc.) has been reported for a long time and by many authors. The possibility for solar influence over the lower atmosphere is hardly acceptable mainly due to the discrepancy between the amplitude of forcing at the top of the atmosphere (small), and the amplitude of cli- mate response (large). There are many hypotheses related to the amplification of the solar signal by different mechanisms but all of them explain only partially the observed quasi-decadal variability of the lower atmosphere. Some authors relate it to the ocean’s This study was partially funded by the Bulgarian National Science Fund, contract No НЗ-1518/05. 845