How Well Do Era-Interim and Merra-2 Capture ITCZ Characteristics and Precipitation?
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The Intertropical Convergence Zone (ITCZ) is one of the most important features of the tropical atmosphere. Recent modeling and observational studies have shown changes in the width and precipitation intensity of this region of the Hadley circulation. The goal of this study is to determine how well existing atmospheric reanalyses capture characteristics of the Pacific ITCZ over the past 35 years using an automated identification algorithm which includes the ITCZ center, width, boundaries, and precipitation intensity within the convergence zone. ECMWF Reanalysis Interim (ERA-Interim) and the second edition of the Modern-Era Retrospective analysis for Research and Applications (MERRA-2) are compared against results obtained using the Global Precipitation Climatology Project (GPCP) observations in Wodzicki and Rapp. The reanalyses are found to be capable of reproducing similar ITCZ characteristics as GPCP, but not without disagreements. The ERA-Interim reanalysis produces a wider ITCZ on average than either MERRA-2 or GPCP, particularly on the southern extent. Analysis of the dynamic and thermodynamics of the two reanalyses shows that ERA-Interim produces a broad region of ascent that does not sufficiently separate the ITCZ and Southern Pacific Convergence Zone (SPCZ) regions in the central Pacific. This lack of separation results in the automated method identifying an ITCZ that extends further south than what is shown by GPCP and MERRA-2. Despite these differences, long-term reanalysis-produced ITCZ trends are similar to observational narrowing and intensification trends, but with varying magnitudes.
Howard, Corey Storm (2018). How Well Do Era-Interim and Merra-2 Capture ITCZ Characteristics and Precipitation?. Master's thesis, Texas A & M University. Available electronically from