Monthly distributions of surface latent heat flux and solar irradiance in the tropical Pacific were computed from observations of the scanning multichannel microwave radiometer on Nimbus-7 and the visible infrared spin scan radiometer on GOES-W. They are the dominant variable components of the surface heat flux, the sum of which gives the approximate thermal forcing on the ocean. Monthly maps of this sum, from January 1980 to September 1983, and within 20 deg N and 20 deg S, 180 deg and 80 deg W, are presented

Frouin, Robert

Gautier, Catherine

Liu, W. Timothy

Tagett, Rebecca

English

NASA Technical Reports Server

JPL Publication 89-42 
Monthly Surface Thermal Forcing 
in the Tropical Pacific 
from 1980 to 1983 
W. Timothy Liu 
Jet Propulsion Laboratory 
Catherine Gautier 
Scripps Institute of Oceanography 
Robert Frouin 
Scripps Institute of Oceanography 
Rebecca Tagett 
Jet Propulsion Laboratory 
November 15, 1989 
NASA 
National Aeronautics and 
Space Administration 
Jet Propulsion Laboratory 
California Institute of Technology 
Pasadena, California 
04 AIM-C-1 7 3)	 MriTFtLY	 Jr°AC	 TI-4LMAL	 NO-L?77 
FORCING IN Ti-if TROPICAL PACIk-IC FROM 1980 TO 
1983 (JPI) 17 p
	
CSCI 08C
&incl as 
G3/48 0264600
https://ntrs.nasa.gov/search.jsp?R=19900013561 2020-03-19T22:09:33+00:00Z
TECHNICAL REPORT STANDARD TITLE PAGE 
1. Report No. 2. Government Accession No. 3. Recipient's Catalog No. 
JPL Pub	 89-42 
4. Title and Subtitle 5. Report Date 
Monthly Surface Thermal Forcing in the Tropical November 15, 19896. Performing Organization Code Pacific 1980-1983 
7. Author(s)w. Timothy Liu; Catherine Gautier; 8. Performing Organization Report No. 
Robert	 Rebecca _Frouin;_	 _Tagett  
9. Performing organization Name and Address 10. Work Unit No. 
JET PROPULSION LABORATORY
11. Contractor Grant No. California Institute of Technology 
4800 Oak Grove Drive NAS7918 
13. Type of Report and Period Covered Pasadena, California 91109 
12. Sponsoring Agency Name and Address 
NATIONAL AERONAUTICS AND SPACE ADMINISTRATION 14. Sponsoring Agency Code D C	 20 46 Washington, 	 . •
	 5 RE4 BP-161-80-15-40-00 
15. Supplementary Notes 
16. Abstract 
Monthly distributions of surface latent heat flux and solar irradiance in the 
tropical Pacific were computed from observations of the Scanning Multichannel 
Microwave Radiometer on Nimbus-7 and the Visible Infrared Spin Scan Radiometer on 
GOES-W.	 They are the dominant variable components of the surface heat flux, the 
sum of which gives the approximate thermal forcing on the ocean. 	 Monthly maps of 
this sum, from January 1980 to September 1983, and within 20.N and 20 9,S, 1800 
and 800 W, are presented in this report; 
17. Key Words (Selected by Author(s)) 18. Distribution Statement 
Meteorology and Climatology; Geosciences 
and Oceanography; Sea Surface Temperatur 
19. Security Classif. (of this report) 20. Security Classif. (of this page) 21. No. of Pages 22. Price 
Unclassified Unclassified 15
JPL 0184 R 9183 
JPL Publication 89-42
to 
Monthly Surface Thermal Forcing 
in the Tropical Pacific 
from 1980 to 1983 
W. Timothy Liu 
Jet Propulsion Laboratory 
Catherine Gautier 
Scripps Institute of Oceanography 
Robert Frouin 
Scripps Institute of Oceanography 
Rebecca Tagett 
Jet Propulsion Laboratory 
November 15,1989 
NASA 
National Aeronautics and 
Space Administration 
Jet Propulsion Laboratory 
California Institute of Technology 
Pasadena. California
This report was prepared at the Jet Propulsion Laboratory, California Institute of 
Technology, under a contract with the National Aeronautics and Space Administration. 
The data were prepared under the Tropical Ocean and Global Atmosphere Heat Exchange 
Project, and jointly supported by the National Oceanic and Atmospheric Administration, 
the National Science Foundation, and the National Aeronautics and Space 
Administration. 
Reference herein to any specific commercial product, process, or service by trade name, 
trademark, manufacturer, or otherwise, does not constitute or imply its endorsement by the 
United States Government or the Jet Propulsion Laboratory, California Institute of 
Technology.
ABSTRACT 
Monthly distributions of surface latent heat flux and solar irradiance in the tropical 
Pacific were computed from observations of the Scanning Multichannel Microwave 
Radiometer on Nimbus-7 and the Visible Infrared Spin Scan Radiometer on GOES-W. 
They are the dominant variable components of the surface heat flux, the sum of which gives 
the approximate thermal forcing on the ocean. Monthly maps of this sum, from January 
1980 to September 1983, and within 200 N and 20° S, 180° and 80°W, are presented in this 
report.
111
CONTENTS 
MONTHLY SURFACE THERMAL FORCING
	 1 
REFERENCES...................................................................................
	 u 
1.	 Distribution of the Sum of Surface Latent Heat Flux and 
Solar Irradiance: January 1980 through June 1980............................3 
2. July 1980 through December 1980................................................. 4 
3. January 1981 through June 1981 .................................................. 5 
4. July 1981 through December 1981 ................................................. 6 
5. January 1982 through June 1982 .................................................. 7 
6. July 1982 through December 1982................................................. 8 
7. January 1983 through June 1983: ................................................. 9 
8. July 1983 through September 1983 .................................................. 10
iv 
MONTHLY SURFACE THERMAL FORCING

IN THE TROPICAL PACIFIC 1980-1983 
The El Niflo Southern Oscillation (ENSO) is one of the most prominent climatic 
signals in time scales from a few months to a few years. An important manifestation is 
the ocean surface warming in the central and eastern equatorial Pacific, with far-
reaching economic and ecologic impacts. Understanding the physical mechanism 
responsible for the sea surface temperature (SST) variability is a major objective of the 
decade-long Tropical Ocean and Global Atmosphere (TOGA) program. Changes in SST 
are largely governed by the balance of surface heat flux, heat advection, and turbulent heat 
transport in the ocean. Until now, the surface heat flux was derived from meteorological 
reports from volunteer ships whose distribution is inadequate to describe the month-to-
month variability. Satellite sensors can provide basin-wide coverage from days to years. 
In the tropical ocean, the latent heat flux and the surface solar irradiance are the two 
dominant variable components of the heat flux. The TOGA Heat Exchange Project 
(THEP) is a research effort initiated to derive these two components, using a combination 
of satellite data (Liu and Niiler, 1985). This report includes monthly maps of the sum of the 
two flux components produced under THEP as an estimation of the surface thermal forcing 
on the ocean. 
The latent heat flux is computed with the model of Liu et al. (1979) which is based on 
the similarity theory in the atmospheric surface layer. The application of this model is 
similar to the use of bulk aerodynamic formulas with variable transfer coefficients which 
depend on atmospheric stability and surface roughness. Over the tropical ocean, the use of 
such a model instead of a constant transfer coefficient is important, due to the weak wind 
and high humidity conditions. At low winds, the surface is aerodynamically smooth and 
the transfer coefficient increases with decreasing wind speed. At high humidities, the 
moisture-induced buoyancy becomes significant in destabilizing the atmosphere and 
increasing evaporation. Using a constant coefficient or one which depends only on the 
temperature stratification would lead to a large underestimation of the evaporation. Like 
any bulk parameterization method, the model of Liu et al. (1979) requires the input of SST, 
wind speed, and humidity. Satellite sensors can measure sea surface temperature and 
wind speed, but not near-surface humidity. They can, however, measure precipitable 
water. Liu (1986) found that, at the monthly time scale, atmospheric water vapor has a 
single dominant mode of variability, and near-surface humidity can be derived from the 
precipitable water measured by microwave radiometers. A global relation was established 
using 17 years of radiosonde reports from 46 mid-ocean meteorological stations. Based on 
this relationship, Liu (1988) computed monthly fields of latent heat flux from 1980 to 1983 in 
the tropical Pacific using data from the Scanning Multichannel Microwave Radiometer 
on Nimbus-7. The results were evaluated with measurements from volunteer ships, 
research moorings, and operational weather stations. 
Employing calibrated visible radiance measurements collected by geostationary 
satellites, Gautier et al. (1980) developed a method of computing daily surface solar 
irradiance. First, the clear sky reflectance is computed as a function of the ocean surface 
albedo and climatological values of atmospheric parameters. This computed clear sky 
reflectance value defines a threshold above which clouds are present. Second, each pixel is 
then tested to define whether it is clear or cloudy. Third, with that determination being 
made, clear or cloudy sky solar irradiance models are applied to compute the 
instantaneous surface solar irradiance. Daily values are obtained by means of a 
trapezoidal time integration procedure, and monthly estimates are determined by 
averaging a varying number of daily values. Based on this procedure, monthly fields of 
surface solar irradiance were computed from observations of the Visible Infrared Spin
Scan Radiometer on GOES-W (Gautier and Frouin, 1989). Validation with measurements 
on research vessels in the tropical ocean were made during GATE (Gautier, 1981) and 
Tropic Heat experiments (Gautier, 1988). 
Limited by the coverage of one geo stationary satellite, the flux fields presented in 
this report are confined to 200 N to 200
 S, 1800
 to 800 W. Microwave radiometer data were not 
available within 600 km from land. The period analyzed extends from January 1980 to 
September 1983 (Figures 1 through 8). Oceanographic implications are discussed by Liu 
and Gautier (1990).
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REFERENCES 
Gautier, C., 1981. Daily Shortwave Energy Budget Over the Ocean from Geostationary 
Satellite Measurements. Oceanogr. from Space, Plenum Publications, Marine Series: 
201-206. 
Gautier, C., 1988. Surface Solar Irradiance in the Central Pacific During Tropic Heat: 
Comparisons Between In-Situ Measurements and Satellite Estimates. J. Clim. 1: 600-
608. 
Gautier C., G. Diak, and S. Masse, 1980. A Simple Physical Model to Estimate Incident 
Solar Radiation at the Surface from GOES-W Satellite Data. J. Appi. Meteor. 19: 1005- 
1012. 
Gautier C., and R. Frouin, 1989. Net
 Surface Solar Irradiance Variability in the Eastern 
Equatorial Pacific during 1982-1985. J. Geophys. Res., submitted. 
Liu, W.T., 1986. Statistical Relation Between Monthly Precipitable Water and Surface-
level Humidity Over Global Oceans. Mon. Wea. Rev. 114: 1591-1602. 
Liu, W.T., 1988. Moisture and Latent Heat Flux Variabilities in the Tropical Pacific 
Derived from Satellite Data. J. Geophys. Res. 93: 6749-6760, 6965-6968. 
Liu, W.T., and C. Gautier, 1990. Thermal Forcing on the Tropical Pacific from Satellite 
Data. J. Geophys. Res., submitted. 
Liu, W.T., KB. Katsaros, and J.A. Businger, 1979. Bulk Parameterization of Air-Sea 
Exchanges of Heat and Water Vapor Including the Molecular Constraints at the Surface. 
J. Atmos. Sci. 36: 1722-1735. 
Liu, W.T. and P.P. Niiler, 1985. Tropical Ocean and Global Atmosphere (TOGA) Heat 
Exchange Project - A Summary Report. JPL Publication 85-49. Jet Propulsion 
Laboratory, Pasadena, CA.
11


Monthly surface thermal forcing in the tropical Pacific from 1980 to 1983

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