Document Type : Research Article
Authors
1
M.Sc. Graduate of Meteorology, Department of Space Physics, Institute of Geophysics, University of Tehran, Tehran, Iran
2
Professor, Department of Space Physics, Institute of Geophysics, University of Tehran, Iran
3
Associate Professor, Department of Space Physics, Institute of Geophysics, University of Tehran, Tehran, Iran
4
Assistant Professor, Faculty of Physics, Yazd University, Yazd, Iran
Abstract
The solar cycle is believed to have an important effect on the stratosphere with some degree of modulation by the quasi-biennial oscillation (QBO). To examine the likely effects of solar cycle and their modulation by QBO, in this study, the JRA-55 reanalysis data with a spatial resolution of 1.25 degrees in both the zonal and meridional directions were used for the period of 1958 to 2017 (60 years in total). Also, the solar flux at a wavelength of 10.7 cm, called , was extracted from the LISIRD website data for the study period. The monthly average temperature, geopotential height and potential vorticity (PV) at 30 hPa level as well as the solar flux were determined for the 60-year duration of the study. The months of the study period were classified into easterly and westerly phases of QBO called EQBO and WQBO, respectively. A similar classificaltion was used for the set of years in which solar activity was greater (lower) than normal, called HS (LS) for high (low) solar. Using the FUB website data, the correlations of temperature, geopotential height and PV at 30 hPa with in the Northern Hemisphere summer (July), early winter (November and December) and late winter (January, February and March) were calculated for the whole set of data and the two subsets obtained for the two phases of QBO. Besides, the changes in temperature and geopotential height between HS and LS phases were investigated.
The main results of this research in terms of solar and QBO phases are as follows. For the temperature and geopotential height at 30 hPa level, the correlations with solar cycle in July are stronger in the subtropics, and larger and spatially wider for the set of EQBO than both the set of all years and the set of WQBO. The correlation of PV with is generally small in July, exhibiting no clear pattern during QBO phases. In early and late winter, For the temperature, geopotential height and PV of 30 hPa, the correlations with are small for the set of all years and the set of WQBO, but attain a relatively large value for the set of EQBO with maximum values found in the tropical regions of both hemispheres. The corresponding correlation pattern for PV is distributed over many regions of both hemispheres with stronger values for the set of EQBO than the set of WQBO. Also, while the temperature and geopotential height difference between HS and LS for the set of WQBO reach their peak in the Southern Hemisphere, there is a spatially wider correlation pattern for the set of EQBO in the tropical regions of both hemispheres. Results also point to a possible impact of solar cycle on the Brewer–Dobson meridional circulation, a topic which needs a separate study.
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