Evaluation of the Surface Radiation Budget in HadGEM1
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Evaluation of the Surface Radiation Budget in HadGEM1. A. Bodas-Salcedo , M. A. Ringer, A. Jones Hadley Centre, Met Office, UK RADAGAST meeting . Reading, ESSC, 19-20 July 2007. Contents. Introduction Motivation Model and data Climatology Seasonal cycles: global and hemipheric

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Evaluation of the Surface Radiation Budget in HadGEM1

A. Bodas-Salcedo, M. A. Ringer, A. Jones

Hadley Centre, Met Office, UK

RADAGAST meeting. Reading, ESSC, 19-20 July 2007


Contents
Contents

  • Introduction

    • Motivation

    • Model and data

  • Climatology

    • Seasonal cycles: global and hemipheric

    • Energy distribution and cloud effects

    • Regional means

  • Comparison against ground measurements

  • Tropical interannual variability

  • Land-surface albedo

  • Global dimming

  • Conclusions


Impact on atmosphere and ocean
Impact on atmosphere and ocean

  • The vertical distribution and overlap of cloud layers determine the magnitude and vertical profile of radiative heating => influence in the large-scale circulation.

  • By modulating the distribution of heating between the atmosphere and the surface, clouds influence the circulation of the oceans.

(Gleckler, GRL, 2005)


Model and observations
Model and observations

  • MODEL

    • HadGAM1 (Atmosphere-only)

    • 1.875o lon x 1.25o lat

    • 38 atmospheric levels

    • 20 years: 1981 - 2000

    • Monthly means

    • 5-member ensemble

  • ISCCP-FD

    • Satellite-derived SRB

    • 2.5ox2.5o approximately equal-area grid

    • 20 years: 1984 - 2003

    • Monthly means

  • BSRN

    • Downwelling fluxes from 28 ground stations

    • ~1800 monthly means

  • MODIS

    • Land-surface white-sky albedo

    • 16-day 0.05 degree albedo product (MOD43C1)

    • MODIS spatially complete albedo

    • 2-yr 16-day averages


Seasonal cycle 60 o s 60 o n
Seasonal cycle (60oS – 60oN)

201.9

210.2

361.1

355.7

9.2

11.2

413.6

418.6



Net fluxes and crf
Net fluxes and CRF

SW

Solid lines:

ISCCP-FD

LW

NET

NET

SW

LW

SW

NET

SW

NET

LW

LW

SW

LW

NET

NET

SW

LW




Bsrn stations
BSRN stations

Climate classification based on Trewartha and Horn (1980)




Hadgam1 vs bsrn seasonal cycles

BSRN

HadGAM1

ISCCP

HadGAM1 vs BSRN – Seasonal cycles

SW

LW


Interannual variability
Interannual variability

ISCCP SWdn

ISCCP LWdn

HadGAM1 SWdn

HadGAM1 LWdn


Surface albedo
Surface albedo

HadGAM1

MOD43C1

HadGAM1

Minus

MODIS

January

July


Surface albedo europe january
Surface albedo – Europe (January)

HadGAM1

Snow amount

HadGAM1

HadGAM1

minus

MOD43C1

MOD43C1

HadGAM1

minus

MODIS-SC

MODIS-SC




Conclusions
Conclusions

  • HadGAM1 simulates reasonably well present day SRB (and the distribution of energy at TOA, ATM and SFC), although notable differences appear at regional level.

  • The biggest differences are found in the Northern Hemisphere.

  • The simulation of LWdn is closer to observations than that of SWdn.

  • SWdn:

    • Overestimation over land masses (ISCCP and BSRN). Bias (StDv): 17.2 (28.6) W m-2.

    • Very good agreement over polar regions.

  • LWdn:

    • HadGAM1 tends to underestimate LWDN. Bias (StDv): -6.0 (19.6) W m-2.

    • Underestimation less consistent than overestimation in SWdn.

    • No significant dependence with latitude, which seemed to be common in previous models.

  • Good representation of the response to El Niño events.

  • Land-surface albedo vs MODIS:

    • +ve bias in January over NH landmasses when compared with.

    • +ve bias over deserts in South Africa, Australia and South America.

    • Lack of structure over the Sahara and Arabian Peninsula.

    • Concerns on the amplitude and phase of the seasonal cycle.

    • Need for comprehensive intercomparison of datasets.

  • Model in line with studies that suggest that ‘global dimming’ is far from being a uniform phenomenon across the globe.




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