Annual cycle of cloud fraction and surface radiative cloud forcing in the

South-East Pacific Stratocumulus region

Virendra P. Ghate and Bruce A. Albrecht (U Miami)

Christopher W. Fairall (NOAA ESRL)

Robert A. Weller (Woods Hole Oceanographic Institution)

• Significant Component of Earth’s radiation budget.

• 20% increase can offset global warming due to doubling of CO2.

• Strong feedback with ENSOKlein & Hartmann 1993

WORS• Wood’s Hole

Oceanographic Institute (WHOI)’s Ocean Reference Station (WORS).

• Location: 20° S 85° W• Continuous observations

of surface broadband radiative fluxes and thermodynamic variables since October 2000.

•http://uop.whoi.edu/archives/dataarchives.htm

Cruise Name Cruise Period

EPIC 2001 Oct 9-25

PACS 2003 Nov 11-24

Stratus 2004 Dec 5-23

Stratus 2005 Oct 5-20

Stratus 2006 Oct 9-27

Seasonal variation of meteorology at WORS

Seasonal Variations: Other Properties

Surface fluxes of sensible and latent heat, LCL, convective velocity scale, and temperature and moisture advection

Estimating Low Cloud Fraction fro a Buoy

cld clrLW CF LW (1 CF) LW

• LW = Measured downwelling longwave radiation at the surface.

• CF = Cloud Fraction

• LWcld = Cloud emitted longwave radiation

• LWclr = Clear sky longwave radiation.

Technique

cld clrLW CF LW (1 CF) LW

• LW = Observed at WORS

• LWcld = σTLCL4

• LWclr = f(qsfc,Tsfc,IVsfc); Fairall et al. 2007

clr

cld clr

LW LWCF

LW LW

Technique Evaluation:Ceilometer Observations

Model-satellite comparison

Seasonal Cycle: Monthly Means

Cloud Fraction

Annual cycle 0.5-0.7

Cloud Forcing: Surface radiative fluxes

Annual Cycle:

Solar -125 to -65 W/m2

IR 55 to 35 W/m2

Diurnal Cycle

Diurnal Cycle Cloud Fraction

Months Range PhaseMean

Night-time

DJF 0.33 18 0.68

MAM 0.22 19 0.59

JJA 0.11 18 0.64

SON 0.23 17 0.79

More Detailed Data Sets

• Annual Cruises

• VOCALS field ProgramFall 2008

http://www.esrl.noaa.gov/psd/people/Simon.deSzoeke/synthesis.html

http://www.eol.ucar.edu/projects/vocals/

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