MPIMetorology

comparing

ISCCP and GEWEX products

Madison, July 2006

Stefan Kinne Max Planck Institute for Meteorology Hamburg, Germany

Ehrhard RaschkeUniversity of HamburgHamburg, Germany

MPI-M

overview

available long-term global data-sets for radiative fluxes at the Top of Atmosphere (ToA) at the surface (sur)

concept on investigating consistency

assessments of solar flux comparisons

assessments of infrared flux comparisons

recommendations

MPI-M

Earth’s radiation budget

how accurate defined is the radiation budget of our climate system?

know your clouds … size-distribution (z) cover (z)

know ancillary data … surface + s-processes anthop. influences

…on regional and seasonal scales

MPI-M

2 long-term data-setsdescribe radiation budgets at ToA and surface

ISCCP GOAL: extract data on cloud field characteristics from

operational meteorological satellite sensors years: 1983-2004, res: 250km (spatial) , 3hr (temp) processedC at NASA-GISS (Rossow, Zhang)

GEWEX-SRB GOAL: determine radiation budgets at the surface years: 1983-2004, res: 100km (spatial) , daily (temp) processed at NASA-Langley (Stackhouse) clouds properties are ‘based‘ on the ISCCP climatology !

MPI-M

task at hand

two bb-flux data sets for same time-period based on the same cloud data

we should expect similar (if not the same) data

let’s test that stratify data into zonal bands of monthly means display differences (always ISCCP minus GEWEX) interpret differences and highlight issues

MPI-M

regional temporal choices

75-90N (1.7%)

60-75N (5.0%) 30-60N (18.3%)

0-30N (25.0%)

0-30S (25.0%)

30-60N (18.3%)

60-75N (5.0%)

75-90N (1.7%)

use monthly averages

MPI-M

solar fluxes

solar ToA the ‘solar’ driver solar surface solar atm.

transmittance solar / surface surface albedo solar / ToA planetary albedo

typical plot: timeseries of monthly averagesdiff.colors for diff.latitude zones

ISCCP -GEWEXdeviation

Time (starting in 1983)

MPI-M

ISCCP – GEWEX sol toa DECEMBER 2005WHY DEVIATIONS ?

simplified treatment ofGEWEX solar insolationat low sun-elevations

for the record: largerdeviations are goneIn new GEWEX data

MPI-M

conclusion # 1

un-necessary deviation for ‘solar driver’

low sun, avg (lat, t)

also an issue in global modeling IPCC-4AR

use consistent routines for ToA insolation !

agree on orbit and So

implement properly!spat/temp integration

-2

-1.5

-1

-0.5

0

0.5

1

80 81 82 83 84 85 86 87 88 89 90 91 92 93 94 95 96 97 98 99

CCS-1368

CCs-1368

CNR-1370

DNM-1368

GFD-1366

GI-1366

GIS-1367

IAP-1380

MPI-1367

MRI-1365

NCA-1367

PCM-1369

PCMOD-1366

-4,22 -6,84

Global annual insolation anomalies (1980 to 1999)

solar insolation of IPCC models

MPI-M

ISCCP – GEWEX sol sur

text

MPI-M

ISCCP – GEWEX sol sur

text

at surface: differences among data-sets are larger !high lat. peaks are out phase to ToA peaks

TOA

a cloud issue !

MPI-M

conclusion # 2

‘sol ToA’ differences are lost at ‘sol surface’ and ‘sol surface’ differences are larger (!)

differences in atmospheric properties dominate larger differences (season dep.) at higher latitudes

most probable explanation diff. in cloud-cover / cloud opt.depth (for data-sets)

assessment: cloud cover / optical depth differ ! ‘cloud’ differences have a seasonal dependence GEWEX cloud (opt. depth/cover) impact is stronger

especially during polar summers (particularly in SH) (… yet weaker during mid-latitude summer in SH)

MPI-M

ISCCP – GEWEX sol / sur

largest differences during NH mid-lat winters- at high latitudes (not shown) even worse !

a snow issue !

MPI-M

conclusion # 3

solar surface albedo in models differs differences have a seasonal dependence sign of diff. varies between high and low latitudes largest differences are linked to snow (alb. / cover)

GEWEX has smaller solar surface albedos at higher latitudes

especially in seasons, when snow can be expected … yet larger solar surface albedos in the tropics

assessment on solar surface albedo: accuracy and consistency of ancillary (non-cloud data) data matters !

MPI-M

ISCCP - GEWEX sol / toa

text

a combination of all previous biases

MPI-M

conclusion # 4

diff. in plantetary albedo display combined effect solar insolation biases solar surface albedo atmospheric properties (especially those of clouds)

potential for offsetting errors

planetary albedo at ToA differences surface albedo diff. at mid/ high lat. are modulated

as expected by cloud impact based on solar transm. - except for tropics: GEWEX clouds less reflective!

assessment: cloud microphysics differ

MPI-M

infrared

IR surface [emission] surf. temp effect IR surface (low) cloud effect IR at ToA [OLR] (high) cloud

effect

ISCCP -GEWEXdeviation

typical plot: timeseries of monthly averagesdiff.colors for diff.latitude zones

Time (starting in 1983)

MPI-M

ISCCP – GEWEX ir sur

text

MPI-M

ISCCP – GEWEX ir sur

textcan this trendbe detected at- ir sur ?- ir toa ?

‘false’ trend due to the use ofincorrect surface temperature data for ISCCP in the tropics

MPI-M

ISCCP – GEWEX ir sur

there NO: atm. effects (clouds) dominate

MPI-M

ISCCP-GEWEX ir toa

text

NO: atm. effects (clouds) dominate

MPI-M

ISCCP-GEWEX ir toa/sur

text

toa

sur

lower GEWEX opt.depth/coverhigher GEWEX opt.depth/cover

MPI-M

conclusion # 5

atmospheric properties are main IR modulators

surface emission differences vs OLR differences usually consistent with cloud (opt.depth/cover) bias … though not always !

cloud boundary temperatures matter atm. temp. profile or altitude placement of cloud?

assessment: cloud altitude placement differs

other important ancillary data: surface temperature / atm. temperature profile

MPI-M

conclusions

ISCCP and GEWEX radiations products often disagree on cloud and ancillary data

significant difference for cloud properties surprise, given the same cloud data-source

larger disagreements at high-latitudes potential offsets can dilute severity of problem

careful validation to quality data are needed ground-based network (BSRN) ? use synergy of advanced space sensors (A-train)

collaboration of data/analyzing groups needed

MPI-M

recommendations

develop a reference algorithm for ToA solar insolation Earth’s orbital data, solar constant, low sun elevation issue

re-evaluate cloud properties and ancillary data (T, snow) compare to in-situ and ground-based quality data identify systematic diff. on regional / seasonal scales

treat cloud and ancillary data in a consistent manner implementation ( … to suit model / data-set resolution)

document your steps ! supply complete and detailed explanations on assumptions

and methods – including a brief summary to allow a hasty user to understand major characteristics and error sources.

MPI-M

MPI-M

extras

solar downward surface flux ‘trend’ solar transmission ratio and ‘trend’ solar planetary ‘trend’ / ‘trend’ differences infrared surf emission ‘trend’ / ‘trend’ differences infrared outgoing ir flux ‘trend’ differences all-sky vs. clear-sky: the cloud effect

MPI-M

MPI-M

ISCCP – GEWEX sol sur

text

MAY 2006

high latitudes only

MPI-M

ISCCP sol sur

text

MAY 2006

lower latitudes

MPI-M

GEWEX sol sur

text

lower latitudes

MAY 2006

MPI-M

MPI-M

ISCCP/GEWEX sol (sur/toa)

text

MPI-M

ISCCP/GEWEX sol (sur/toa)

text

MPI-M

GEWEX sol (sur /toa)

text

MPI-M

MPI-M

ISCCP – GEWEX sol / toa

text

lower latitudes

MPI-M

ISCCP – GEWEX sol / toa

text

high latitudes

MPI-M

ISCCP sol / toa

text

MPI-M

GEWEX sol / toa

text

MPI-M

MPI-M

ISCCP – GEWEX ir sur

text

MPI-M

ISCCP ir sur

text

MPI-M

MPI-M

ISCCP-GEWEX ir toa

text

lower latitudes

MPI-M

ISCCP – GEWEX ir toa

text

high latitudes

MPI-M

MPI-M

ISCCP-GEWEX cld effect solsur

text

MPI-M

ISCCP cloud effect sol / toa

text

MPI-M

ISCCP cloud effect ir toa

text

MPI-M

ISCCP 91-95 sol+ir toa

text

Raschke et al., Int.J. Clim. 2005

MPI-M

ISCCP 91-95 sol+ir atm

text

Raschke et al., Int.J. Clim. 2005