| Based on the Merra-2 and NCEP/NCARI reanalysis data from 1980 to 2020,the temporal and spatial distribution of tropopause gradient in the northern hemisphere and its relationship with upper-level wind temperature are studied.The results show that the intensity and location of the center of tropopause gradient change obviously with the seasons,and the gradient is the steepest from the middle east of our country to the middle of the Pacific Ocean(30 ° N-35 ° N,90 ° E-165 ° E)in winter,the mean value of the center is 36 Pa/km,the frequency of tropopause strong slope is the highest in this area.The trend analysis shows that the tropopause gradient area in the northern hemisphere is slowly approaching the equatorial direction,and the time variation characteristics of tropopause gradient over Japan,Korea and Central Asia are similar,and the difference in months was significant,the maximum difference was 21 Pa/km.the time variation characteristics of tropopause gradient over the northern Pacific and the northern Atlantic are similar,with a gradient of about 20-30 Pa/km.The monthly variation of tropopause gradient over the northern Asian region is similar to that over the Greater Sunda Islands region,and the gradient fluctuated at 20pa/km and 10pa/km,respectively.And the tropopause gradient over the region over Japan and South Korea and the Northern Pacific region is significantly correlated with the high-altitude zonal winds below,especially in winter and spring,the greater the slope,the higher wind speed area under the jet stream Axis moved southward obviously,and vice versa.Similarly,the tropopause gradient in this region is significantly correlated with the potential temperature above and below the tropopause,especially in winter and spring.The higher the tropospheric top slope,the higher the potential temperature is,and the lower the potential temperature is,the more stable the stratification is. |
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