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An Examination of the Radiative Fluxes in Various Reanalyses with an Emphasis on the Global Budget Wesley Ebisuzaki 1 , S. K. Yang 1,2 , Li Zhang 1,2 , Arun Kumar 1 1 NOAA Climate Prediction Center, Camp Springs, Maryland 2 Wyle Science Technology and Engineering, McLean, Virginia.

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An Examination of the Radiative Fluxes in Various Reanalyses with an

Emphasis on the Global Budget

Wesley Ebisuzaki1, S. K. Yang 1,2, Li Zhang1,2, Arun Kumar1

1NOAA Climate Prediction Center, Camp Springs, Maryland

2Wyle Science Technology and Engineering, McLean, Virginia

OSR climatologies

Introduction

The OSR follows the sun and is weaker as you approach the North Pole. The spread is larger then for the OLR. CFSR, ERA-interim and MERRA are not as con-sistent as with the OLR.

Most of the reanalysis projects are based on the forecast models and data assimilation systems used in the numerical forecasting of weather. In the data assimilation, there are no constraints on the annual global energy balance at the top of the atmosphere. However, if there were a net imbalance in the energy budget, the observations or the lower boundary condition would have to adding or removing the thermal energy.

This study will show the top-of-atmosphere radiative fluxes from various reanalyses: CFSR, ERA-interim, JRA-25, MERRA, NCEP/NCAR Reanalysis (R1) and NCEP/DOE Reanalysis (R2). For these reanalyses, the global outgoing long-wave radiation (OLR) ranges from 237 W/m/m (R1) to 255 W/m/m (JRA-25). Most of the reanalyses have more OLR than the 239 W/m/m that was estimated by Trenberth et al (BAMS, 2001). The outgoing short-wave radiation flux (OSR) at the top of the atmosphere was estimated to be 109 W/m/m by Trenberth et al. and was within the range of the various reanalyses estimates (94 W/m/m of JRA-25 to 117 W/m/m of R1). The net global imbalance ranged from -6 W/m/m to 13 W/m/m.

  • Data: Monthly mean data converted to a 192x94 Gaussian grid. The reanalyses used:
    • CFSR: Reanalysis from Climate Forecast System version 2 (Saha et al. 2010)
    • ERA-Interim: Reanalysis from ECMWF (Dee et al. 2011)
    • JRA: Japanese 25-year Reanalysis Project (Onogi 2007)
    • MERRA: Reanalysis (Rieneckeret al 2009)
    • R1: NCEP/NCAR reanalysis (Kalnay et al 1996)
    • R2: NCEP/DOE reanalysis (Kanamitsu et al. 2002)
    • The climatologies were calculated from 1979-2008.

TOA Global Radiation Budget

OLR climatologies

Global 12-month running mean OLR. Consistent results except for R1 and JRA-25. Other reanlayses range between 242 and 246 W/m/m. No secular trends.

Global 12-month running mean of net radiative flux. (Upwards is positive). ERA-interim is within 3 W/m/m of radiative balance. CFSR and MERRA are close to be being balanced but show secular trends.

Global 12-month running mean OSR. R1 is an outlier, larger range for other reanalyses. Drop in CFSR recent years. More trends than in OLR time series.

The uncertainty in the January OLR is situated over subtropical belt and in particular South America. Outside of the sub-tropics, the spread is small, about 10 W/m/m. The ERA-interim and CFSR climatologies are in agreement with themselves and the ensemble mean. Both of these reanalyses are within 5 W/m/m over much of the globe. MERRA was in more disagree-ment with the newer reanalyses especially in the extratropics.

Summary

The uncertainty in the July OLR shifted north and with peak uncertainty in the Caribbean. The CFSR and ERA-interim are again in close agreement with each other and the ensemble mean. The MERRA shows much more convention over the Caribbean and the Northern Indian ocean and subtropical Western Pacific.

The agreement in the OLR climatologies between the newer reanalyses is sign that the con-vectiveclouds are more con-sistentthat in the older models.

One expects that the models used by the reanalyses to improve. Signs of improvement are the reanalyses becoming consistent and the systems becoming more in balance. We examined the OLR and OSR and found that the newwer reanalyses are producing more consistent OLR (4 W/m/m with the new systems). However, the OSR is a different story. The OSR estimates show a larger variability than the OLR and the new reanalyses don’t show a strong evidence of converging.

The global incoming radiation must be balanced by the outgoing radiation and the heat storage term. Averaging over one or more years should reduce the size of storage term and one would expect a near balance of the incoming and outgoing radiation. The ERA-interim has an imbalance of 3 W/m/m. MERRA has an imbalance of 4 W/m/m in the early period and approaches zero in the later period. The CFSR has an imbalance of 2 W/m/m until something happens (around 2010).

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