Hk. Lee et al., On the annual cycle of latent heat fluxes over the equatorial Pacific using TAO buoy observations, J METEO JPN, 76(6), 1998, pp. 909-923
In this paper, we describe the annual cycle in the latent heat flux (LHF) a
nd its associated bulk variables (sea surface temperature, wind speed, humi
dity difference) over the equatorial Pacific. The in-situ, daily-averaged T
AO buoy observations between 8 degrees N and 8 degrees S during the period
1992-1996 form the database. LHF was computed using a modified bulk paramet
erization scheme to account for active convection and low wind speed freque
ntly observed in the western Pacific. Harmonic analysis was used to help qu
antify the phase and amplitude of the annual and semiannual cycles.
The annual cycle of LHF was found to be conspicuous in two regions, namely,
the northeastern and western/central Pacific. For the former region, the m
aximum LHF occurs in boreal summer and early fall, when surface wind speeds
are strong and the temperature difference between sea surface and air near
the bottom of the atmospheric boundary layer is large. For the western/cen
tral Pacific, maximum LHF occurs in boreal winter, when the winter monsoon
is strong. In contrast to the aforementioned two regions, the annual cycle
in LHF in the equatorial cold tongue is weak and low LHF prevails throughou
t the year. Also noted in this study is a westward propagation of the maxim
um LHF region from the northeastern Pacific around July to the western Paci
fic by the following March.
We also ascertained the relative importance of dynamic and thermodynamic pr
ocesses in regulating the month-to-month variations of the LHF along two me
ridional transects, one in the eastern and another in the western Pacific.
In the eastern Pacific, except to the north of the cold tongue, variations
in humidity difference (i.e., thermodynamic process) seem to be of primary
importance to the annual variations in LHF. On the other hand, variations i
n wind speed (i.e., dynamic process) are more important to the LHF in the w
estern/central Pacific.