Editorial Type:
Article
Article Type:
Research Article

Rainfall and Convection in ERA5 and MERRA-2 over the Northern Equatorial Western Pacific during PISTON

Yolande L. Serra aCooperative Institute for Climate, Ocean, and Ecosystem Studies, University of Washington, Seattle, Washington

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https://orcid.org/0000-0003-3542-1158
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Steven A. Rutledge bColorado State University, Fort Collins, Colorado

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Kyle Chudler bColorado State University, Fort Collins, Colorado

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Chidong Zhang cPacific Marine Environmental Laboratory, NOAA, Seattle, Washington

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Online Publication:
13 Jan 2023
Print Publication:
01 Feb 2023
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Air–Sea Interactions from the Diurnal to the Intraseasonal during the PISTON, MISOBOB, and CAMP2Ex Observational Campaigns in the Tropics
DOI:
https://doi.org/10.1175/JCLI-D-22-0203.1
Page(s):
845–863
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Abstract

This study evaluates rainfall, cloudiness, and related fields in the European Centre for Medium-Range Weather Forecasts fifth-generation climate reanalysis (ERA5) and the National Aeronautics and Space Administration’s Modern-Era Retrospective Analysis for Research and Applications, version 2 (MERRA-2), gridded global reanalysis products against observations from the Office of Naval Research’s Propagation of Intraseasonal Tropical Oscillations (PISTON) field campaign. We focus on the first PISTON cruise, which took place from August to October 2018 in the northern equatorial western Pacific Ocean. We find biases in the mean surface heat and radiative fluxes consistent with observed biases in high and low cloud fraction and convective activity in the reanalyses. Biases in the high, middle, and low cloud fraction are also consistent with the biases in the thermodynamic profiles, with positive biases in upper-level humidity associated with excessive high cloud in both products, whereas negative biases in humidity above the boundary layer are associated with too few low and middle clouds and increased static stability. ERA5 exhibits a profile that is more top-heavy than that of MERRA-2 during periods dominated by MCSs and stronger upward motion during rainy periods, consistent with higher total rainfall in this product during PISTON. The coarser grid size in MERRA-2 relative to ERA5 and the fact that MERRA-2 did not assimilate PISTON data likely both contribute to the overall larger biases seen in MERRA-2. The observed biases in the reanalyses during PISTON have also been seen in comparisons of these products with satellite data, suggesting that the results of this study are more broadly applicable.

© 2023 American Meteorological Society. For information regarding reuse of this content and general copyright information, consult the AMS Copyright Policy (www.ametsoc.org/PUBSReuseLicenses).

Chudler current affiliation: Center for Water Resources, RTI International, Fort Collins, Colorado.

This article is included in the Air-sea interactions during PISTON, MISOBOB, and CAMP2Ex - Air-sea interactions from the diurnal to the intraseasonal during the PISTON, MISOBOB, and CAMP2Ex observational campaigns in the tropics; Special Collection.

Corresponding author: Yolande L. Serra, yserra@uw.edu

Abstract

This study evaluates rainfall, cloudiness, and related fields in the European Centre for Medium-Range Weather Forecasts fifth-generation climate reanalysis (ERA5) and the National Aeronautics and Space Administration’s Modern-Era Retrospective Analysis for Research and Applications, version 2 (MERRA-2), gridded global reanalysis products against observations from the Office of Naval Research’s Propagation of Intraseasonal Tropical Oscillations (PISTON) field campaign. We focus on the first PISTON cruise, which took place from August to October 2018 in the northern equatorial western Pacific Ocean. We find biases in the mean surface heat and radiative fluxes consistent with observed biases in high and low cloud fraction and convective activity in the reanalyses. Biases in the high, middle, and low cloud fraction are also consistent with the biases in the thermodynamic profiles, with positive biases in upper-level humidity associated with excessive high cloud in both products, whereas negative biases in humidity above the boundary layer are associated with too few low and middle clouds and increased static stability. ERA5 exhibits a profile that is more top-heavy than that of MERRA-2 during periods dominated by MCSs and stronger upward motion during rainy periods, consistent with higher total rainfall in this product during PISTON. The coarser grid size in MERRA-2 relative to ERA5 and the fact that MERRA-2 did not assimilate PISTON data likely both contribute to the overall larger biases seen in MERRA-2. The observed biases in the reanalyses during PISTON have also been seen in comparisons of these products with satellite data, suggesting that the results of this study are more broadly applicable.

© 2023 American Meteorological Society. For information regarding reuse of this content and general copyright information, consult the AMS Copyright Policy (www.ametsoc.org/PUBSReuseLicenses).

Chudler current affiliation: Center for Water Resources, RTI International, Fort Collins, Colorado.

This article is included in the Air-sea interactions during PISTON, MISOBOB, and CAMP2Ex - Air-sea interactions from the diurnal to the intraseasonal during the PISTON, MISOBOB, and CAMP2Ex observational campaigns in the tropics; Special Collection.

Corresponding author: Yolande L. Serra, yserra@uw.edu
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