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Abstract
The response of the atmospheric circulation to global warming is still not well known. A specific area of interest is the westerlies of the Northern Hemisphere, most notably the strengthening or weakening of the westerlies, which could change mid-latitude weather patterns. Previous studies have termed the phrase tug-of-war idea, which is the interaction between the warming of the tropics and the warming of the Arctic, with opposite jet response to each. This study focused on the difference between specific areas of the tropics and Arctic for two different time periods. The first was the future using 30-year RCP8.5 (2070-2099) minus 30-year historical (1975-2004) climate model run outputs for temperature change and zonal wind change. The second was the satellite era (1979-2018) using concatenated historical and RCP8.5, halved into two 20-year periods, Past (1979-1998) and Present (1999-2018), and taking the difference between those two periods for the same climate model outputs. For the future period, using 41 climate models from CMIP5, a robust correlation was found between the strengthening (weakening) of the westerlies and warming of the tropics (Arctic). Specifically, for every degree of difference in warming between the Arctic troposphere (60-90°N, 850-300 mb) and subtropical troposphere (20-40°N, 850-200 mb) the mid-latitude zonal wind response (30-70°N, 1000-200 mb) decreased by -0.5 ms-1 (r = -0.9245). A strong correlation was also found for the satellite era, using 91 ensemble members from 42 climate models, using the same parameters for the atmosphere from the future period above that showed a decrease in mid-latitude zonal wind response of -0.47 ms-1 (r = -0.7643) per degree of warming difference. This strong correlation in the satellite era will allow future studies to be performed using observations from reanalysis and/or microwave satellite data to determine which models are expected to be more accurate