Hadley cell dynamics in Japanese Reanalysis-55 dataset: evaluation using other reanalysis datasets and global radiosonde network observations

Abstract

Hadley circulation (HC) is a planetary scale circulation spanning one-third of the globe from tropics to the sub-tropics. Recent changes in HC width and its temporal variability is a topic of paramount interest because of the climate implications it carry alongside. The present study attempts to bring out the subtropical climate change indications in the comparatively new Japanese Re-analysis (JRA55) dataset by means of the mean meridional stream function (MSF). The observed features of HC in JRA55 are found to be reproduced in NCEP, MERRA and ECMWF datasets, with notable differences in the magnitudes of MSF. The calculated annual cycle of HC edges, center and total width from this dataset closely resembles the annual cycle of the respective parameters derived from the rest of the datasets, with very less inter-annual variability. For the first time, MSF estimated using four reanalysis datasets (JRA55, NCEP, MERRA and ECMWF datasets) are verified with observations from integrated global radiosonde archive datasets, using the process of subsampling. The features so estimated show a high degree of similarity amongst each other as well as with observations. The monthly trend in the total width of the HC is quantified to show a maximum of expansion during the month of July, which is significant at the 95 % confidence interval for all datasets. The present paper also discusses the presence of a ‘minor circulation’ feature in the northern hemisphere which is centered on 34°N during the June and July months, but not in all years. The significance of the present study lies in evaluating the relatively new JRA55 datasets with widely used reanalysis data sets and radiosonde observations and revelation of a minor circulation not discussed hitherto in the context of HC dynamics.