Observed Reductions of Surface Solar Radiation at Sites in the United States and Worldwide from 1961 to 1990

Beate Liepert

• Lamont-Doherty Earth Observatory of Columbia University

and NASA Goddard Institute for Space Studies, New York

• presently at MPI for Meteorology, Hamburg

References:

Liepert, B. G., 2002. Observed reductions of surface solar radiation

in the United States and worldwide from 1961 to 1990.

Geophys. Res. Lett., 29(10), 1421.

Feichter, J. et al., 2002. Effects of Air Pollution on the Hydrological

Cycle. Poster presentation IGAC 2002.

www.ldeo.columbia.edu/~liepert

“ Absence of warming” in the United States, Hansen et al., 2001.

MFRSR Lamont Observatory, Palisades NY

Global Energy Balance Archive GEBA, Gilgen et al., 1998.

• Quality tested data base from World Radiation Data Center (WRDC)

• Broadband surface solar radiation measurements (0.3m - 30m)

• 252 records of monthly averages

• Monthly decadal means and differences for each record

(1961 to 1970, 1971 to 1980, 1981 to 1990)

Global Energy Balance Archive:

Decadal Mean Surface Solar Radiation for 1981 to 1990

W/m2

Changes of Decadal Mean Surface Solar Radiation: 1981 - 1990 minus 1961-1970

W/m2

F = -7W/m2

United States

F = -19W/m2

1961 - 19701971 - 19801981 - 1990

Former Soviet Union

F = -2W/m2

National Solar Radiation Data Base of the United States NSRDB, Maxwell et al. 1995.

Composites of ‘all’, ‘clear’, and ‘overcast’ sky conditions of each decade retrieved from additional cloud cover information of observer estimates.

33 records of broadband surface solar radiation in hour resolution from 1961 to 1990. (not complete!)

1961 - 19701971 - 19801981 - 1990

Overcast skies

United States sites

F = - 18W/m2

Clear skies

United States sites Liepert/Tegen, JGR 2002

F = - 8W/m2

Cloud Coverage % and Cloud Cover Frequencies of Various Cloud Conditions at United States Sites (Ac* broken cloudy coverage, Ac total cloud coverage)

0

0.1

0.2

0.3

0.4

0.5

0.6

Broken cloud coverageAc*

Total cloud coverageAc

1961-70 1971-80 1981-90

0

0.05

0.1

0.15

0.2

0.25

0.3

0.35

0.4

0.45

0.5

clear cloudy overcast

• From 1960s to 1980s observed global decline in surface solar radiation of 7 W/m2 or 4% and 19 W/m2 or 10% decline in the United States

• Clear sky less transparent and• Clouds optically thicker in the United States • Strongest reduction of surface solar radiation under “opaque” clouds

• Changes in cloud coverage: more overcast skies, less clear skies and unchanged total cloud coverage

Summarizing Results of Observational Data Analysis:

Surface cooling and tropospheric heating

Combined Effects of Greenhouse plus Aerosol Forcing,Feichter et al., 2002 IGAC Poster.

• Climate simulations with ECHAM4 GCM (atmosphere plus mixed layer ocean), fully coupled aerosol model HAM (Feichter, Lohmann, Roeckner), 176 years run, statistics over the last 50 years

• Verification see Kinne et al. IGAC 2002 poster presentation

• Two equilibrium experiments:“Present day” PD scenario: greenhouse gases and aerosol concentrations of ~1985“Pre-industrial” PI - scenario: greenhouse gases and aerosol concentrations of ~1870

• Assumption: differences PD - PI representative for climatic change

Reduction in net surface solar radiation in the United States and Europe.

“No change” in modeled cloud coverage in the United States and Central Europe.

Increase in liquid water content of warm clouds (increase in cloud optical thickness)

Less surface evaporation when solar radiation is reduced.

Consequences for the hydrological cycle:

Increase in soil wetness

Hypothesis:•Soil wetness as climate memory •Anthropogenic aerosols over land important for water storage (more important than cloud modification?)•Increasing risk of flooding even without increasing precipitation

All sky effect: F = - 19 W/m2

Overcast cloud effect: Fo = - 18 W/m2

Clear sky effect: Fcl = - 8 W/m2

United States Germany

All sky Clear sky Overcast Opaque All sky Clear sky Overcast

1961-70 2004 2433 12810 958 1245 1904 474

1971-80 1945 2423 12111 849 1224 1904 443

1981-90 1817 2356 11014 7511 1204 1933 423

Observed 10-year Means of Surface Solar Radiation.

Partitioning of surface solar radiation

oclcd

ic

icc

ccdclccdoooclcl

fff

ii

cwithcfA

AfFAfFfFfFF

i

i

1

9,...,2,10

)1(

*

**

All sky change of surface solar radiation at United States sites from 1960s to 1980s with fixed fcl, fo:

F = F(1980s) - F(1960s) = - 13 W/m2

Partitioning of 10-year Means of Surface Solar Radiation of the United States Sites

Radiation W/m2 Clear + cloud-free

fraction of

cloudy

Overcast + Cloud-

covered fraction of

cloudy

Calculated

all sky F

Observed

all sky Fobs

1961 - 70 124 (80 + 44) 61 (28 + 33) 185 200

1971 - 80 116 (70 + 46) 62 (31 + 31) 178 194

1981 - 90 105 (63 + 42) 60 (33 + 27) 165 181

Calculated: F(1980s) - F(1960s) = F = - 20 W/m2

Observed: Fobs (1980s) - Fobs (1960s) = Fobs = - 19 W/m2