How Well Does ERA-Interim Capture ITCZ Characteristics and Precipitation?

Numerous recent studies have suggested that the region of heavy precipitation corresponding with the Intertropical Convergence Zone (ITCZ) becomes both narrower and more intense with greenhouse gas forcing scenarios. Analysis of observational data such as the Tropical Rainfall Measuring Mission (TRMM) and Global Precipitation Climatology Project (GPCP) in the current climate has shown a decrease in meridional extent of the ITCZ as well as an increase in precipitation intensity. Mechanisms have been proposed in the literature that suggest horizontal inflow of drier air along the margins of the deep convective regions reduces the area of precipitation, while a series of feedbacks leads to enhanced low-level moisture convergence in regions with a predisposition for upward motion and intense precipitation. Between observational analysis and this so called rich get richer effect found in many global climate model studies, we have some confidence in decrease of ITCZ extent and increased precipitation intensity. Here we first test the precipitation data rendered from the ERA-Interim reanalysis and then assess its viability for testing these hypothesized mechanisms. ITCZ precipitation metrics including rainfall, extent, and intensity will be compared against observations to establish whether reanalysis accurately captures the features of the ITCZ. Preliminary results imply that the ERA-Interim rain rates are more intense and extend further meridionally than observational data. Despite these differences, ITCZ long-term precipitation trends are similar. To better understand the dynamics and thermodynamics of the ITCZ changes, an examination of moisture transport into the heavy precipitation region will be conducted using the reanalysis to determine whether mechanisms proposed for ITCZ variability under greenhouse warming are evident in the current climate. This analysis will help to provide insight into the validity of ERA-Interim reanalysis physics and to better understand the dynamics and thermodynamics that contribute to the narrowing and intensification of the ITCZ.