IHY 2008, Sozopol, Bulgaria1 N. A. Kilifarska 1, Y. K. Tassev 2 1 Geophysical Institute, Bulgarian Academy of Sciences 2 Solar-Terrestrial Influences Laboratory, Bulgarian Academy of Sciences

IHY 2008, Sozopol, Bulgaria2 Motivation for this study Major stratospheric warmings (MSWs) affect dramatically the whole winter atmosphere till the surface; Mechanisms relevant to SSW are still not clear; Existence of solar and internal atmospheric modes ( i.e. QBO, AO, ENSO ) in the polar atmospheric variability is broadly documented; 2 main types of MSWs: −Vortex displacement −Votex spliting After: Charlton and Polvani, J. Climate, Feb.2007

IHY 2008, Sozopol, Bulgaria3 Data and Methods Data: CRs ( energetic particles measured by GOES satellites at km ) for three winters , and in which 2 MSWs had occured; Ground-based μ monitor at Climax ( 42.21N; W ); Daily values of F 10.7 ; T, winds and O 3 mixing ration – from ERA 40 6 hourly analyses, for the period ; Indices of internal atmospheric modes, i.e. Arctic oscillation index (AO) and QBO ( quasi biennial oscillation of the equatorial stratospheric winds ) Methods: multiple regression and lagged correlation analyses

IHY 2008, Sozopol, Bulgaria4 The aim of this study: To reveal the existence of causal relationships between some observed atmospheric parameters and forcing factors (i.e. solar and CRs variability and atmospheric internal modes like QBO, AO, etc.) To offer an explanation for existing great variety of Stratospheric Warmings, i.e.: –minor; –major (splitting type and displacement type); –Canadian.

IHY 2008, Sozopol, Bulgaria5 Zonal wind distribution

IHY 2008, Sozopol, Bulgaria6 Some elementary statistics for MSWs: Initial guess : possible influence of highly energetic cosmic rays on polar atmospheric thermodynamics due to a strong control of active solar wind on CRs intensity. Correl. Coeff. for F 10.7 and CRs time series: (west QBO) (east QBO) Displacement type MSWsSplitting type MSWs High Solar ( 5 ) Low Solar ( 8 ) High Solar ( 5 ) Low Solar ( 9 ) HS(e)HS(w)LS(e)LS(w)HS(e)HS(w)LS(e)LS(w)

IHY 2008, Sozopol, Bulgaria7 MSWs during Low Solar radiation conditions I. Wind correlation with ground based measurements of CRs

IHY 2008, Sozopol, Bulgaria8 II. Temperature and wind correlations with CRs measured on GOES satellite – winter (west QBO) Conclusion: Intense CRs precipitation within periods of Low Solar radiation and west QBO favor decrease of Polar Vortex size eroding its equatorward edge. According to the model experiments of Scott and Dritshel, 2006 => volumes’ ratio of Aleutian Anticyclone and Polar vortex plays an important role in the process of vortex splitting

IHY 2008, Sozopol, Bulgaria9 Vortex-Vortex interactions in the Winter Polar Atmosphere I. After: R. Scott and D. Dritshel, J. Atmos.Sci., 63, 726, 2006 Volumes’ ratio (Aleutian high/Polar Vortex)=0.6 t=0t=2 dayst=4 days t=6 days t=8 days t=10 days

IHY 2008, Sozopol, Bulgaria10 Vortex-Vortex interactions in the Winter Polar Atmosphere II. t=0t=8 dayst=16 days Volumes’ ratio (Aleutian high/Polar Vortex)=0.2

IHY 2008, Sozopol, Bulgaria11 “Displacement” type MSWs  CRs showers during Low solar radiation and east QBO, however seems to force anticyclonic circulation trough decrease of westerlies over the Polar Cap;  Distortion of equilibrium between Aleutian high and Polar vortex could provoke a movement of the anticyclone toward the Pole and displacement of Polar Vortex;  The mostly affected by CRs is Nort-East part of Canada (due to the less geomagnetic cutoff) => creation of anticyclonic vortex in North Atlantic 1987

IHY 2008, Sozopol, Bulgaria12 MSWs occurred within periods of High Solar Irradiance Lagged cross-correlation analysis of forcing factors show: within QBO(e) phase AO is significantly influenced by F 10.7 (+0.42) and QBO amplitude (+0.30) during QBO(w) phase AO index has stochastic character

IHY 2008, Sozopol, Bulgaria13 U regression coefficients for winter , HS, QBO(w), “displacement” type

IHY 2008, Sozopol, Bulgaria14 Zonal wind correlations with CRs measured on GOES satellite – winter

IHY 2008, Sozopol, Bulgaria15 CONCLUSIONS An attempt for setting in order the great variety of conditions for occurrence of Major Strat. Warms is made. It was found that: 1.within periods of Low Solar irradiance CRs’ showers may affect the dynamical structure of Polar Atmosphere as well as to be the key factor for occurrence of different types Major Stratospheric Warmings, namely “spliting” and “displacement” types; 2.During High Solar activity periods: For QBO(e) phase solar electromagnetic radiation and the amplitude of QBO affect significantly dynamical regime of the Polar Atmosphere operating more effectively trough AO index; For QBO(w) AO index have stochastic character and this reduces possibilities for predictions; 3.In periods of very active Sun, solar electromagnetic radiation and corpuscular particles in a “trio” with QBO may affect strongly atmospheric dynamics at middle and high latitudes.