[A-AS05] Weather, Climate, and Environmental Science Studies using High-Performance Computing

[AAS05-P03] Asymmetrical Responses of the ITCZ to Symmetrical Thermal Forcings at Different Latitudes

Xinyu Ma¹, *Shuyun Zhao^1,2, Weichong Huang¹, Hua Zhang^1,2,3, Wuke Wang¹, Lunche Wang⁴ (1.Department of Atmospheric Sciences, School of Environmental Studies, China University of Geosciences, Wuhan, China, 2.Key Laboratory of Meteorological Disaster, Ministry of Education/Collaborative Innovation Center on Forecast and Evaluation of Meteorological Disasters, NUIST, 3.State Key Laboratory of Severe Weather, Chinese Academy of Meteorological Sciences, China Meteorological Administration, Beijing, China, 4.Department of Geography, School of Geography and Information Engineering, China University of Geosciences, Wuhan, China)

Keywords: ITCZ, tropical precipitation, asymmetric response, CESM model

Meridional shifts of the intertropical convergence zone (ITCZ) in response to tropical or extratropical forcings have been investigated widely within an emerging energy framework. However, few studies examined the sensitivity of the forcing spatial pattern. This work explores the dependence of the ITCZ response on the patterns of thermal forcings, which are hemispherically antisymmetric and zero in global mean, using the Community Earth System Model coupled with a slab ocean. Results show that the magnitudes of ITCZ displacements caused by mid-latitude perturbations are larger than their low-latitude counterparts, though the perturbation amounts are the same in hemispheric average. It is found that mid-latitude perturbations cause more cross-equatorial atmospheric energy transport (AET, the upper branch) and moisture transport (the lower branch), together consisting of an anomalous Hadley cell. The reason lies further in the different mechanisms of precipitation response to low- and mid-latitude thermal perturbations. That is when perturbations are added in the tropics, evaporation and clouds immediately respond together, limiting the magnitude of either one; while when perturbations are added in mid-latitudes, local evaporation responds first, followed by low-level moisture transport to the tropics initiating the tropical cloud response. The misalignment allows the two to respond fully. Results also show that the zonal mean precipitation responses have asymmetry even though the warming and cooling are symmetric; that is the increase of precipitation in the warmed hemisphere is more poleward than the decrease of precipitation in the cooled hemisphere. This is especially true when the mid-latitudes of the southern hemisphere (SH) are warmed. The phenomenon is a manifestation of the precipitation and Hadley circulation interactions. And that the asymmetry of precipitation response is greater in the case of warming SH than those in the case of warming the northern hemisphere is attributable to the offset of AET by transient eddies in the latter case.