This was a Tropical Rainfall Measurement Mission (TRMM) modeling, analysis and applications research project. Our broad scientific goals addressed three of the seven TRMM Priority Science Questions, specifically: What is the monthly average rainfall over the tropical ocean areas of about 10(exp 5) sq km, and how does this rain and its variability affect the structure and circulation of the tropical oceans? What is the relationship between precipitation and changes in the boundary conditions at the Earth's surface (e.g., sea surface temperature, soil properties, vegetation)? How can improved documentation of rainfall improve understanding of the hydrological cycle in the tropics

Busalacchi, Antonio J.

Lagerloef, Gary

Liu, W. Timothy

Lukas, Roger B.

Niiler, Pern P.

Swift, Calvin T.

English

NASA Technical Reports Server

(NASA-CR-[89437) NASA TROPICAL
RAINFALL MEASUREMENT MISSION
(TRMM): EFFECTS OF TROPICAL
RAINFALL ON UPPER OCEAN OYNAMICS_
AIR-SEA COUPLING AND HYDROLOGIC
CYCLE Final Report (Science
Applications) 9 p G3/47
N95-31123
Unclas
0058470
https://ntrs.nasa.gov/search.jsp?R=19950024702 2020-06-16T06:37:45+00:00Z
CR-189437
I
NASA Tropical Rainfall Measurement Mission (TRMM)
f ....
Final Report: Contract NAS5-:3t458-- ._/-_ ._J'_
Effects of Tropical Rainfall on Upper Ocea/n Dynamics, Air-Sea Coupling and Hydrologic
Cycle .....
Principal Investigator
DR. GARY LAGERLOEF, Science Applications International Corporation
13400 Northup Way N'E, Suite 36B, Bellevue, WA 98005
Telephone: (206)747-7152 FAX: (206)747-9211
Co-Investigators
Antonio J. Busalacchi (GSFC), W. Timothy Liu (IPL), Roger B. Lukas 03. Hawaii), Pearn P.
Niiler 03CSD), Calvin T. Swift 03. Mass.)
Summary This was a Tropical Rainfall Measurement Mission (TRMM) modeling, analysis
and applications research project. Our broad scientific goals addressed three of the seven
TRMM Priority Science Questions, specificaUy:
What is the monthly average rainfall over the tropical ocean areas of about 10s kin2;
and how does this rain and its variability affect the structure and circulation of the tropical
oceans?
What is the relationship between precipitation and changes in the boundary conditions
at the Earth's surface (e.g. SST, soil properties, vegetation)?
How can improved documentation of rainfall improve understanding of the
hydrological cycle in the tropics?
Knowledge of (1) how rainfall affects the dynamics and air-sea fluxes of the tropical upper
ocean, and (2) rates of recycling of freshwater in the tropical ocean-atmosphere, remain as
fundamental problems in our understanding of the climate system. It is these scientific issues
to which we directed our research. In an effort to develop a coordinated approach to these
problems, we brought together a group of investigators with expertise in remote sensing,
numerical modeling, surface observations, analysis, oceanography and meteorology in a
modest effort to coordinate several on-going studies into a coherent science investigation for
TRMM. Work under this proposal focuses on the TRMM science discussed above, utilizing
several planned observations and studies for Tropical Ocean Global Atmosphere (TOGA) and
the TOGA Coupled Ocean Atmosphere Response Experiment (COARE). Funds were
requested here only for activities relating directly to the TRMM science goals and not
otherwise covered by other programs. Funding cuts during the course of the project made it
impossible to complete all the objectives of the original proposal. Nevertheless, significant
progress was made, as summarized below.
Surface temperature, salinity and remote sensing (Lagerloef) Temperature and salinity in
the surface 3 cm of the ocean were obtained from RN Wecoma during COARE (Lagerlocf,
et al, 1993; Paulson and Lagerloef, 1993). A special sampler was developed for this
experiment, involving a surface towed hose drawing seawater pumped through a
thermosalinograph. The objectives were I) to study the very near surface rain response at
depths much shallower than the 2 m to 5 m depths conventionally sampled with continuous
shipboard sampling systems, and 2) to better understand the relationship the very near surface,
or skin, properties seen by remote sensing and the bulk, or mixed layer, temperatures and
salinities.
Some results from surface sampler data during heavy rainfall episodes arc shown in Figure 1
in comparison to measurements made at 2 m from a sensor mounted on the ship's bow. The
surface (-3 cm) showed a sharp response to the cool and freshwater rain with depressed
temperatures and salinities while the response at 2 m was small by comparison, indicating
that the freshwater was retained in a shallow surfac_ lens during the active rainfall. Other
low salinity/temperature anomalies not coincident with rain indicate that the ship passed
through residual lenses formed by earlier rain events. These data will be included in the
larger TOGA COARE data base, and used to describe the degree of decoupling between skin
and bulk values caused by lens formation, the studies of mixed layer models, heat and
fre.shwater fluxes, and freshwater budgets in the COARE IFA.
Shipboard observations and analyses OLukas): During the IOP, R/V Wecoma towed
Seasoar depth-cycling vehicles, carrying conductivity, temperature, depth (CTD) sensors to
obtained high verticaland along-trackresolutionmeasurements of tamperatureand salinityin
the upper 300 m. Repeated surveys were conducted in the butterfly pattern of the IFA. From
these data, daily averages of mixed layer depth, temperature and salinity have been computed
and a portion is shown in Figure 2. The mixed layer salinity decrease in early January
coincides with the onset of heavy atmospheric convection and precipitation observed during
the COARE IOP.
Mixed layer,isohaline,and isothermallayerdepth estimateshave been compared to the local
momentum, heat,and moisture fluxes. Preliminaryresultssuggestthatfor strongenough
winds, the freshwater flux is not very important, while for weaker winds, k may make the
differencebetween a wind event destroyingthe barrierlayer or not. The importance of such
dynamics on the structure of the upper layer and the air-sea heat flux is a fundamental
scientificissuefor TOGA COARE. This effortalsoincluded preliminary analysisof TAO
mooring data,includingraingages,and development of a Lagranglan mixed layermodel to
assessthe effectsof advection on the saltbudget and stratification.
Surface drifter observations (Niiler) TOGA COARE includes a program centered on
Lagrangian techniqueswith satellite-tracked(ARGOS) driftersby which we can study how
the upper ocean in the warm pool isforced by the wind, heated and freshenedover dailyto
monthly time scale,s. Approximately 50 drfftexsper year,for a two year period beginning
mid-1992, were programmed for the western tropicalPacific.The resultingdata setwill
provide measurements of velocityU, temperature T and salinityS as well as dU/dt,dT/dt and
dS/dt following the drifters(Niiler,1990). Analysis objectivesforthiseffortare to estimate
the long-term average balance of dT/dt and dS/dt followingthe fluidparcels. Our preliminary
results indicate that our estimates will provide a strong and unique constraint on the heat
budget in the warm pool region; we expect that our estimates of dS/dt will provide a similar
constraint for the freshwater budget. From these, the upper ocean in sittt convergence of
freshwater will be computed to compare with rainfall. As an example of this calculation,
fields of U have been collected from the Comprehensive Ocean Atmosphere Data Set
(COADS) ship drift observations and fields of S have been collected from the Levitus
climatology to compute the steady mean annual freshwater convergence (i.e. salinity
divergence), which is the left hand side of
U.VS E-P
8 h
where h is the mixed layer depth. The map of the mean annual freshwater convergence of
the tropical Pacific is shown in Figure 3. The negative values (dashed contours) signify the
regions where precipitation exceeds evaporation, and these clearly denote the bands of tropical
rainfall in the ITCZ and SPCZ. These maps will be analyzed in conjunction with E-P
estimates from satellites (below) to evaluate the consistency between E-P derived from the
upper ocean freshwater convergence vs satellite. This can serve as an important validation
tool for TRMM rain products on large spatial and seasonal to interannual time scales.
Numerical modeling (Busalacehi) In support of TOGA COARE, A. J. Busalacehi, in
collaboration with Dake Chen and Law Rothstein, studied the physical processes that are
responsible for the maintenance and variability of the warm pool in the western tropical
Pacific Ocean and its influence on the large scale tropical Pacific Ocean heat budget. This
numerical modeling effort has highlighted mixed layer physics of the equatorial ocean, with
special emphasis on upper ocean mixing and an investigation of possible salinity effects with
future application to TRMM studies in mind. More specifically, this effort was designed to
use a rather unique combination of explicit one-dimensional mixed layer models and a large
scale tropical ocean circulation model that they have recently modified to include active
hydrology. Initial experiments were configured with what were felt to be the minimum
requirements to capture the physics of the tropical upper ocean and were run under idealized
foreings in a model tropical Pacific basin. Subsequent experiments were designed to utilize
realistic geometries under observed forcing to provide simulations of the upper tropical
Pacific Ocean. The ultimate goal was the development of a computationally efficient tropical
Pacific upper ocean model that would be appropriate for studies of the warm pool response to
momentum and buoyancy forcing.
Evaporation, precipitation and fluxes (Liu) From the conservation principle, the ocean
surface fresh water flux (evaporation-precipitation) has to be balanced by the change of water
storage and the water divergence in the atmosphere. The difference between evaporation and
precipitation will be primarily balanced by the horizontal water vapor transport. Each of
these terms will be computed, with developing satellite methods. Precipitation can be
computed as the residue of E-P, with evaporation computed separately from bulk formula
using SSMI, and compared with satellite retrievals. This is the core of one of the on-going
studies of W.T. Liu, presently supported by the NASA Interdisciplinary Science and
Hydrologic Cycle Programs. The present TRMM project has been carried out in collaboration
to include the hydrologic balance in the ocean, with the focus in the tropical Pacific, utilizing
salinity and current measurements from other co-investigators and from TOGA COARE.
3
VIRS team leader and VIRS validation (Lagerloef) An interim VIRS science team was
formed in 1992 from a subset of TRMM Project Science Team members with interest in the
VIRS data, and Lagerloef was appointed chairman. The VIRS team provided scientific
guidance to the TRMM Project regarding VIRS hardware and calibration issues. Certain
hardware issues were monitored. Of greatest concern are the 12 micron channel sensitivity
and the performance of the radiative cooler.
Salinity Remote Sensing (Lagerloef and Swift) We originally planned to make salinity
remote sensing observations from the NASA DC-8 during TOGA COARE, but it was not
possible to include ESTAR on that or any other aircraft designated to participate in the field
program. Alternatively, we proceeded with a plan to make observations from a radiometer
mounted on the RN Wecoma during Leg 3 of the COARE IOP. The radiometer
measurements are consistent with modeled values for salinity, temperature and incidence
angle. However, as luck would have it, there was very little rain encountered by the ship and
consequently no significant salinity variations observed by the in situ calibration sensors,
during the portions of the Leg 3 cruise when the radiometer was operating. As such, we did
not achieve the primary objective of calibrating the sensor response to oceanic salinity
variations in the warm pool.
Publications and Presentation Abstracts
Chen, D., L. M. Rothstein, and A. J. Busalacchi, 1993a. A hybrid vertical mixing scheme
and its application to tropical ocean models. Submitted to I. Phys. Oceanogr.
Chen, D., A. J. Busalacchi, and L. M. Rothstein, 1993b. Simulation of the seasonal cycle in
the tropical Pacific Ocean. In preparation for submittal tO ]'PO, 8/93.
Huyer, A., M.Kosro, C.Paulson, R.Lukas, E. Firingand P.Hacker, 1993: Thcrmohaline
structureof the upper ocean in the COARE IntensiveFlux Array. EOS Trans.AGU, 74,
1993 FallMeeting (Abstract).
Lagerloef, G., C. Swift and D. LeVine, 1995: Sea surfacesalinity:The next remote sensing
challenge. Oceanography (submitted)
Lagerloef, G., C. Paulson, J.Aleksa and C. Wilson, 1993: Rain-caused near surfacesalinity
fluctuationsin the western Pacificwarm pool during TOGA COARE (Abstract),Third
ScientificMeeting of the Oceanography Society,Seattle,Wa.
Lagerloef, G.S.E.,C.T. Swift,D.M. Le Vine and A. Griffis,1992, "Remote Sensing of Sea
Surface Salinity:Airborne and SatelliteConcepts," AGU Ocean Sciences Meeting, New
Orleans, January 1992 (Abstract).
Li, X. and P.Niiler,1994: Wind driven currentin the upper mixing layerover the equatorial
PacificOcean. EOS Trans.AGU, 75, 1994 Ocean Sciences Meeting (Abstract).
Lukas, R. 1993: The TOGA COARE westerly wind burst and the oceanic response.
Abstracts of the Air-Sea Interaction Symposium, Oct. 25 1993, Sendai Japan.
Lukas, R. and P. Webster, 1993: TOGA COARE: Ocean and atmosphere Interactions I.
EOS Trans. AGU, 74, 1993 Fall Meeting (Abstract).
Lukas, R., E. Firing, P.Hacker, A.Huyer, M.Kosro, C.Paulson, 1993: The upper ocean
response to the December 1992 westerly wind burst. EOS Trans. AGU, 74, 1993 Fall
Meeting (Abstract).
Paulson, C.A. and G. Lagerloef, 1993: Fresh surface lenses caused by heavy rain over the
warm pool of the western Pacific Warm Pool during TOGA COARE, EOS Trans. AGU, 74,
1993 Fall Meeting (Abstract).
Shinoda, T and R. Lukas, 1995: Lagrangian mixed layer modeling of the western equatorial
Pacific. L Geophys. Res., in press.
Soloviev, A., R.Lukas, S.Asghar, D.Khlebnivov, 1993: Coherent structures near the air-sea
interface in the western Pacific warm pool. EOS Trans. AGU, 74, 1993 Fall Meeting
(Abstract).
5
©Figure I
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TOGA COARE measurements from R/V Wecoma, Leg 2 (14 Dec 1992-16 tan 1993).
Top to bottom: wind speed; surface(dark lin¢) and 2 mClight line) temperature; surface and 2
m salinity; rain temperature; rain ram and ship speed. Abscissa is day of year in 1993
(3.0=0000 GMT 3 1anuary, 1993). Conspicuous diludon took place during the heavy rain
episodes ('indicated by the vertical dashed lines), forming shallow lenses of cooler, fre,shef wa_r.
Signature, s at the 2 m depth wera much smaller than at the surfaca. Afar the second large
rainfall episode, the ship passed through a low salinity lens remnant from an earlier rainf-aIl.
(From Paulson md Lagerioef, 1993).
15
j,..[
Figure 2
Daily average estimatesbased on shipboard Seasoaf CTD data in theTOGA COARE
IntensiveFlux Array (IFA), Dec 1992 - fan 1993: Top panel: mixed layea depth h and depth
of the top of the thermocline; Middle panel: Mixed layer temperature 7"; Bottom panel: _K_.xed
layer salinity S. Such estimates of h and S will be used with other measurements to estimate the
freshwater bu..dget within the IFA.
17
oFigure 3
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,[., y i I I I I
_'_"C..-" -t_-_-: ,,-,,, . ,,
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" I I I I I I I
120. 160. 200. 240. 280.
logitude
Estimate of the mean annual freshwater convergence (U*VS)IS based on COADS ship
drift data for U and Levitus climatology for S. This yields an estimate of CE-?)/h, where h is
the mixed layer depth. The dashed contours, where E-P<O, coincide with the heavy
precipitation zones of the ITCZ and SPCZ.
" "_ _,,,,_', _.__..'---- .'--'" __ .... . ',_ " " -"
=o- , , . ".-._.... ...... _-..::f..__..__.__ q
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.r ._ ...- " .-L ---:----_"--_. -."='_""_"" _ : - : - ........... "-..
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_¢'1! I i -_ _" , " " '
"_20 140 160 180 200 220 240 260 280
Longitude
GPCP mean annual monthly rainfall from SSMI data (Chang, et al, 1993). Note that
the bands of high precipitation coincide with the estimates of freshwater convergence from ocean
surface data
18
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1. AGENCYUSEONLY (Leaveblank) 2. REPORTDATE 3. REPORTTYPEAND DATESCOVERED
January 1995 Contractor Report
4. TITLEAND SUBTITLE 5. FUNDINGNUMBERS
NASA TRMM Effects of Tropical Rainfall in Upper Ocean Dyamics,
Air-Sea Coupling and Hydrologic Cycle
6. AUTHOR(S)
Principal Investigator: Gary Lager]oef
7. PERFORMINGORGANIZATIONNAME(S)AND ADDRESS(ES)
Science Applications International Corporation
13400 Northup Way, NE
Suite 36B
Bellevue, WA 98005
9. SPONSORING/MONITORINGAGENCYNAME(S)ANDADDRESS(ES)
NASA Aeronautics and Space Administration
Washington, D.C. 20546-0001
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CR-189437
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13. ABSTRACT(Maximum200 words)
12b. DISTRIBUTIONCODE
This was a Tropical Rainfall Measurement Mission (TRMM) modeling, analysis and applications research project.
Our broad scientific goals addressed three of the seven TRMM Priority Science Questions, specifically: What is the monthly
average rainfall over the tropical ocean areas of about 105 km 2, and how does this rain and its variability affect the structure
and circulation of the tropical oceans? What is the relationship between precipitation and changes in the boundary conditions
at the Earth's surface (e.g., SST, soil properties, vegetation)? How can improved documentation of rainfall improve under-
standing of the hydrological cycle in the tropics?
14. SUBJECTTERMS
Tropical Rainfall, Tropical Ocean Global Atmosphere (TOGA), Upper-Ocean Dynamics,
Air-Sea Coupling, Hydrologic Cycle
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NASA Tropical Rainfall Measurement Mission (TRMM): Effects of tropical rainfall on upper ocean dynamics, air-sea coupling and hydrologic cycle

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