The 11-year solar cycle, the 27-day Sun's rotation and the area of the stratospheric Aleutian high

Abstract

The effect of the 11-year solar cycle on the 30-hPa geopotential height and temperature fields in the area of the Aleutian high caused by solar activity oscillations resulting from the Sun's rotation (27.2 d) is investigated, applying methods of statistical cross-spectral analysis to daily data for the period from 1965 to 1998. The area of the stratospheric Aleutian high is considered as an indicator of the solar influence on the winter stratosphere proceeding from the results by LABITZKE and VAN LOON (1988), and VAN LOON and LABITZKE (1990). An effect of the 11-year solar cycle on the response of the summer middle stratosphere to solar activity oscillations on the time scale of the Sun's rotation is not found. In contrast to summer, the atmospheric responses in winter demonstrate clear differences between maximum and minimum of the 11-year solar cycle for the 27.2 d solar rotation periodicity and for the two other oscillations of 29.4 d and 25.3 d, resulting from the modulation of the 27.2 d solar-induced periodicity by the annual atmospheric variation. The atmospheric response for the fourth periodicity studied, the 17 d oscillation, which is supposed to be a normal mode of the atmosphere, close to the known 16-day wave (MADDEN, 1978), also shows a clear dependence on the 11-year solar cycle. For all the periodicities studied the coherence between the 10.7 cm solar radio flux and the 30-hPa height/temperature fields in the Aleutian high area in winter is on the average stronger at maxima than at minima of the 11-year solar cycle. The corresponding amplitudes of the solar-induced geopotential height and temperature perturbations are also larger at high than at low solar activity, with the largest differences revealed at the moderate and polar latitudes. Thus, we conclude that the response of the winter 30-hPa height/temperature fields in the area of the Aleutian high to solar oscillations on the time scale of the Sun's rotation is on the average stronger at high than at low solar activity. We suppose that the influence of the 11-year solar cycle on the stratospheric Aleutian high area includes the modulation of the intensity of interaction between the solar induced 27 d oscillation and seasonal atmospheric variations.