DATE: Friday, April 26, 2019 TIME: 11:00 am, refreshments at 10:45 am PLACE: ENR building, room 334 14 College Farm Road, New Brunswick, NJ
Allison Collow
Universities Space Research Association, Columbia, MD. NASA GSFC Global Modeling and Assimilation Office, Greenbelt, MD.
An Overview of MERRA-2 and the Influence of Prescribed Boundary Conditions on Near-Surface Temperature over the Arctic
Reanalyses have become a valuable tool to study weather and climate due to their consistencies in temporal and spatial resolution, as well as model parameterizations and assimilation techniques, throughout a time span of decades. NASAâs latest reanalysis product, the Modern Era Retrospective analysis for Research and Applications, version 2 (MERRA-2) is no exception and has been used for a variety of scientific studies and purposes ranging from input for modeling studies to engineering pavement and wind farms. The talk will begin with aspects of MERRA-2 that make it unique in addition to how the data set is produced using NASA satellite observations and an incremental analysis update. Despite improvements in reanalysis products over the years, uncertainties still remain in our understanding of the climate in data scarce regions such as the Arctic. Discrepancies are present in the surface temperature over the Arctic in modern reanalysis products with MERRA-2 standing out with a cold bias over the past decade compared to other reanalyses. While reanalyses use different methodology and data sources for sea surface temperature and sea ice concentration boundary forcing, MERRA-2 and the ERA-Interim reanalysis have a recent overlapping period that use the Operational Sea Surface Temperature and Sea Ice Analysis, however the rest of the time series uses varying sources for boundary forcing. Furthermore, an ensemble of 37 year AMIP-style simulations using the MERRA-2 atmospheric model without data assimilation shows drastically different temperatures over the Arctic, especially in the fall and winter months. In an effort to test the effect of prescribed sea surface temperature and ice datasets, a sensitivity experiment was performed such that the boundary forcing stemmed from ERA-Interim instead of what was used to produce MERRA-2. A cross comparison of surface temperatures over the Arctic from the two reanalyses and two AMIP-style ensemble simulations will be presented along with the implications of varying temperature time series on the atmospheric circulation and energy budget.