Statistically Significant Estimates of Influence of Solar Activity on Planetary Waves in the Middle Atmosphere of the Northern Hemisphere as Derived From Muam Model Data

Abstract

Numerical simulation has been used to examine the effect of changes in solar activity (SA) in the thermosphere on amplitudes of long-period planetary waves (PW) for the winter period in the Northern Hemisphere. The model of the middle and upper atmosphere (MUAM) is used. It allows simulations of general atmospheric circulation at altitudes 0–300 km. In order to reproduce SA changes, different values of the solar radio flux at a wavelength of 10.7 cm at an altitude of more than 100 km are set in the MUAM radiation block. To take into account the effect of charged particles in the ionosphere on the neutral gas dynamics, ionospheric conductivities for different SA levels are included in MUAM. To improve the statistical reliability of the results, two ensembles of model simulations consisting of 16 runs corresponding to the minimum and maximum SA have been obtained. The statistical confidence of average differences in PW amplitudes between high and low SA has been calculated. The results are shown to be reliable in almost the entire altitude range 0–300 km. Results of the simulations have shown for the first time that statistically significant differences in amplitudes of long-period PWs can reach 10–15 % in the middle atmosphere of the Northern Hemisphere, depending on the zonal wave number. At the same time, reflection of PWs at altitudes of lower thermosphere has a significant effect on the PW structure in the middle atmosphere.

Dynamical Impacts of Stratospheric QBO on the Global Circulation up to the Lower Thermosphere

“…A similar conclusion can be made when considering the region closer to the pole, where, on the contrary, there is a deceleration of the zonal flow, a decrease in the EP flux divergence, and an increase in the meridional thermal gradient. A statistical significance of the obtained increments in wind and temperature was calculated based on standard formulas with the approach described by Koval (2019). At each grid node of the latitude-altitude distribution, the paired Student's t-test is applied for 32 values (16 pairs of model runs * 2 months).…”

“…The initial and background conditions for all model calculations are taken to be identical. A detailed description of the features of statistical processing of data from ensembles of simulations is presented in Koval (2019).…”

“…A statistical significance of the obtained increments in wind and temperature was calculated based on standard formulas with the approach described by Koval (2019). At each grid node of the latitude‐altitude distribution, the paired Student's t ‐test is applied for 32 values (16 pairs of model runs * 2 months).…”

Sensitivity of the 4–10-Day Planetary Wave Structures in the Middle Atmosphere to the Solar Activity Effects in the Thermosphere

“…Averaging over 16 model runs and over two months allowed us to achieve 95% statistical significance and diminish effects of extreme atmospheric processes such as sudden stratospheric warming events, which occur in individual MUAM runs. The statistical processing of the ensemble results based on Student's t-test is described by Koval [27].…”