Impact of inter-seasonal solar variability on the association of lower troposphere and cold point tropopause in the tropics: Observations using RO data from COSMIC

Abstract

Association of lower tropospheric variations with the cold point tropopause (CPT) is examined on inter-seasonal basis over the tropical region (30°N-30°S) during 2007–2010 using COSMIC/FORMOST-3 Radio Occultation (RO) data. Temperature analyses for this association are shown over different regions of the globe having contrast topography namely over Western Pacific sector, Indian sector, and African sector. Correlation coefficient (r), taken as a measurement of association, show specific longitudinal differences between the lower troposphere (from 1km to 5km height) and the CPT. The northern and southern hemispheres show contrast coupling of temperature variation between lower tropospheric region and the CPT. Land and ocean effects are found to contribute in a different way to the correlation coefficient. Analyses show symmetrical structure of ‘r’ on both sides of the equator over the African region, as data include mostly land region on both side of equator. Data represent positive correlation (r~0.5) over 15°–20° latitudes on either side of the equator over the African region, suggesting strong hold of the inter-seasonal variation of solar diabatic heating influence over the tropic of Cancer and tropic of Capricorn. On the other hand, there is a contrast behaviour over the Indian region, ‘r’ is nearly negative (~−1.0) each year in the southern hemisphere (SH) and positive (~0.4) in the northern hemisphere (NH) with a maxima near tropic of Cancer. Western Pacific region is found to display a linear increase in ‘r’ from negative (~−1.0) in SH to positive (~0.8) in NH. In general, ‘r’ (positive) maximizes over the land region around 15°–20° latitudes, suggesting a control of in phase inter-seasonal solar heating on the coupling of boundary layer/lower troposphere and CPT region, whereas it turns negative over water body. Analyses suggest that variabilities in CPT over different regions of globe show significant inter-seasonal association with the lower troposphere. Thus CPT variabilities are not only governed by QBO, ENSO, gravity waves and Kelvin wave system as reported in earlier studies but also considerably affected by inter-seasonal changes taking place in the lower troposphere.