Significant accomplishments in the last year of research are presented. During 1991, three main activities were undertaken: (1) development and testing of a preliminary global rainfall algorithm; (2) researching areas of strong surface scattering; and (3) formulation of a program of work for the WetNet PrecipWG. Focus of present research and plans for next year are briefly dismissed

Barrett, Eric C.

Kidd, C.

Kniveton, D.

English

NASA Technical Reports Server

Global Rainfall Monitoring by $SM/I
B.C. Barrett, C. Kidd and D. Kniveton
N93-20069
Background ofthe lnve_agation
Rainfall is a key environmental parameter for which In situ observational data has
always been generally inadequate. Today, the need for rainfall data Is even greater
than before, not least because of growing concerns for global weather and climate
change, improved evaluations of the global hydrological cycle, and the significance
of rainfall for water supplies, crop growth, industry and comnw, rcc. Since the
1970s many techniques have been tested for improved rainfall monitoring using
satellite visible and/or infrared data in support of ground observatlons. However,
problems existwithallsuchmethods becausetheradiancesmeasured by thesatellite
emanate almostexclusivelyfrom thetopsof clouds.Passivemicrowave dataafford
freshhope for more physicallydirectmonitoringof rainfallby satellites,especially
forclimatetimescales.
The WetNet Project, "a pilot programm¢...des|gned to enhance scientific analysis
and encourage an interdisciplinary approach to research problems" is based on the
DMSP-SSMH sensor, and therefore holds particular promise for rainfall
monitoring. The activity described in this Report is part of the WetNct effort,
which embraces a total of 42 laboratories, 7 outside the USA. A key element of
WetNet is ...%ooperative research among teams of scientists...*; the WelNet
Precipitation Working Group is the biggest of its teams. Since early 1991
E.C.Barrctt has served (at NASA's request) as WetNct PrccipWG Chairman. In
this capacity he has organised a global algorithm precipitation int, rcomparison
project (PIP-I) as outlined below.
$[gnificam Accomplistwaents In the la._t year
During 1991, three main activities were undertaken:
l, I_eyelooment and testing of a prelim inarygl_bal rainfall _lgodthm, based on
frequency differencing over land and polarization diftcr¢nclng over coasts and
oceans. Initial results (including both global maps and mean latitudinal profil©s
of estimated rainfall) have been compared qualitatively with climatology, and
areas of difficulty identified. The latter include area.s of strong surface
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aP._tt_ng, most notably sand and snow.
Researching areas of strong surf'ace scattering in attempts to reduce or even
remove related global rainL'all algorithm ambiguities, Results for selected
desert areas (Sahara, Great Australian Desert) confirm that use of horLzontally-
polarized brightness tcmpe_tures in su_ areas in.stead of the more g_crally
approved veurdcally-poladzed data largely eliminate thc sand/rainfall ambiguity
problem, Meanwhile, studies in se.Jectedsnow-covezcd areas (Orc_t Britain)
confirm thatrain/snowambiguitiesare likelyto be more difficultto resolve,
althoughevaluationsof diurnaltemperaturevariationsof snow surfacesmay be
helpfulin some situations.Global testshave begun wlth a modif'md global
raJnfa]i algorithm Incorporating the above findings, and the results from
possiblythefirstsuchalgorithmtoeschew a sandmask areencouraging.
Formulation of a pin,yam of.work for the WetNet Pree|pWG, pdmariiy the
Precipitation lntercomparlson Project, Pip-l, to be undertaken during 1992.
Recognising that present SSM/[ rainfall algorithms are not yet mature, but
increasing calls are being made for such algorithms to be implemented
operationally, PIP-I was proposed by E.C.Ba.rrett,
(a) to facilitateil_ of existingalgorithms(including$$MII,
OPCP infrared,Spencer MSU, and ECMWF forecastmodel outputs)
and through requested resultsconforlning to a careful set of
specificationsfor a chosen periodof tlme (August throughNovember
1987, for which data from _1 seven $SM/I channels were available);
Co) to permit _ of these results through reference to selected surface
data sets (GPCC continental raingauge, and Motrlsey's Pacific atoll,
data sets);
(c) to enable_ of the physicalreasonsfordifferingresultsfrom
differentalgorithms;and
(d) to move towards the _ of a "community algorithm" for
optimum performanco on a global scale.
A sub-committee of F.,CB (Chair), l.Dodge (NASA, HQ), l.Janowlak (CAC,
NOAA), M, Goodman (NASA, MSFC) and E.$mith (FSIY) w_ set up to
prepare the "rules of combat', and to determine how the results will be
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¢vahated. Invitationlettersto possibl¢PIP-1 particLpantsWCl'¢sentout in
December 1991, and ancillaryand validationdata setswens obtained. A
subsoquent case-study oriented PIP-2 Is now being advanced from seed to
embryo.
Focus of Prezem Research and Plar_ for Next Year
Presently, we arc preparing our own results for submission to PIP-I by the dcadlitm
of 31 luly 1992, and designing the statistical package by which _sults from all
participating laboratories w111be judged. From 1 August until 4 January 1993 we
will,inliaisonwithMSFC, processand analysetheseresults.
It is our intention in 1993 to prepare a detailed Report on the intetcomparison in
time for a Participant's Workshop provisionally set for 13-14 April 1993. Aftex this
we will complete and edit a special edition of the rcfere.ed Journal
(approx. 200pp) to dascribe PIP-l, its need, its components, and its results
and their implications. For the second half of the year w© hope to participate in the
planned PIP-2 (case studies) exercise, and follow-on activities from PIP-1 as its
r_ults recommend, it is expe.ctcd that ECB will contlnu¢ to Chair the PrccipWO
through this period.
Barrett, l_.C. (1991): Diagnostic, historic & predictive analyses of rainfall using
passivo microwave image data. Palacogco_eraphy, Palaeoclimatology &
_, 90, I99I, p.99-106,
Barrett, E.C. & Bellcrby, T.L (in pros): A strategy for the calibration by conateral
data of satellite rainfall estimates for shormr peflods. Accepted for
publication In Journal of Applied Mcteor01o_v.
Barrett, B,C,, Kidd, C. and Kniveton, D. (1992): Global Rainfall Monitorin_ by
the SSM/I: Products. Problems and Intercomparison Projects. Final Report
to USRA, Columbia, MD., RSU, Univ. Bristol 83pp + 27pp of Plains.
Barrett, E.C., Kidd, C. & Xu, Hui. "Snow monitoring by AVHRR-HRPT and
DMSP-SSM/I data analyses'. In Proceedings of the Vth AVHRR .Users
_ding, "lh'omso, Noway, 1991, p. 103-108.
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GLOBAL SATELLITE DATA ANALYSIS
John R. Christy
Assistant Professor, Atmospheric Science
University of Alabama in Huntsville
and
Roy W. Spencer, NASA/MSFC
1. Microwave Sounding Unit Research (with Roy Spencer)
Papers in press:
Spencer, R.W. and J.R. Christy, 1992: Precision and radiosonde validation of
satellite gridpoint temperature anomalies. Part I: MSU Channel 2. J.
Climate, 5.
Spencer, R.W. and J.R. Christy, 1992: Precision and radiosonde validation of
satellite gridpoint temperature anomalies. Part II: A tropospheric
retrieval and trends during 1979-90. J. Climate, 5.
Trenberth, K.E., J.R. Christy and J.W. Hurrell, 1992: Monitoring global
monthly mean surface temperatures. J Climate, 5.
Papers in review
Spencer, R.W. and J.R. Christy, 1993: Precision lower stratospheric
temperature monitoring with the MSU: Technique, Validation, and
Results 1979-90. ]. Climate.
Contributions to books:
Christy, J.R., "Monitoring Global Temperature Changes from Satellites".
Chapter 11. Global Climate Change: Implications, Challenges and
Mitigation Measures. Eds: S.K. Majumdar, L.S. Kalkstein, B. Yarnal,
E.W. Miller, and L.M. Rosenfeld. The Pennsylvania Academy of
Science.
Conference Presentations:
(invited) Spencer, R.W. and J.R. Christy, 1991: A physical interpretation of
brightness temperatures observed by the Microwave Sounding Units
based upon Raobs. Fifth Symposium on Climate Variations, American
Meteorological Society, 14-18 Oct. 1991, Denver CO.
Christy, J.R. and K.E. Trenberth, 1991: Monitoring global monthly surface
temperatures. Fifth Symposium on Climate Variations, American
Meteorological Society, 14-18 Oct. 1991, Denver CO.
? P_ING P/IK;.-E BLANK NOT FILMED
(invited) Christy, J.R., 1991: The MSU data, 1979 to the present. First
Demetra Meeting on Global Change, 28 Oct. 1991, Chianciano Italy.
Other
Invited Contributor, Climate Change 1992: IPCC,Supplementary Report
(Section C,Observed Climate Variability and Change). Melbourne Australia,
24-26 Nov. 1991.
Research areas:
Working with Spencer to develop a multi-channel retrieval for increased
tropospheric precision. The problem area concerns the instability of channel
3 on at least three of the MSUs.
Using footprint data, I am constructing global synoptic maps of MSU
temperatures (daily means at this point) for identification of variability over
data sparse regions on the synoptic scale.
2. Earth Observing System
(In addition to papers listed above)
Papers presented:
Christy, J.R., R.T. McNider, F.R. Robertson and D. Fitzjarrald, 1991:
Comparison of MSU and CCM1 tropospheric temperatures for 1979-86.
Fifth Symposium on Climate Variations, American Meteorological
Society, 14-18 Oct. 1991, Denver CO.
Christy, J.R., 1992: Climate model validation using MSU global temperatures.
Workshop on Atmospheric Model Intercomparison Project. 21 Feb.
1992, Berkeley, CA.
Research Areas
One result from the multi-year run of the CCM1 using prescribed (observed)
SSTs (1978-86) indicated that the model's tropospheric temperature responds
to SST warming almost exactly as does the real atmosphere as measured by
MSU temperatures. However, during periods of cooling, the CCM1 did not
return to the levels seen in the real atmosphere so that a warm bias slowly
was built in the model results. At present the net downward solar flux in the
tropics is being examined and found to vary in the opposite sense from
atmospheric temperature (warmer troposphere indicates more cloudiness).
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This seems to be a negative feedback on temperature, though not to the extent
experienced in the real world.
D. Fitzjarrald, J. Srikishen and I are studying the predictability of global
stratospheric and tropospheric temperatures using neural network theory.
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Global rainfall monitoring by SSM/I

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