INTRODUCTION
Flux observation have been carried out on the head of cape at Japanese south-east island in order to obtain following insights;
(1) the vertical heat fluxes over the sea surface as the boundary condition of the atmospheric boundary layer meteorology,
(2) the lateral heat fluxes within the sea as the truth of global scale energy dynamics, and
(3) the local turbulent flow dynamics over such complex landscape as the cape.
SITE and MEASUREMENTs
An observation tower with 10 m height have been installed on the head of the Cape Nishi-henna-saki, Hirara city, Okinawa, JAPAN. The cape is the northern edge of Miyako Island located on N24o54.5', E125o15.5'. We have conducted the measurement from 13th through 27th August 2002. Measured items are summarized as follows;
Wind vector (10Hz) at 10.2m and 3.7m
Temperature (10Hz) at 10.2m and 3.7m
Vapor and CO2 density (10Hz) at 10.2m
Solar and reflective radiation at 9.7m
Atmospheric radiation at 9.7m
Wind speed at 9.8, 7.1, 4.8, 2.6m
Temperature & Humidity at 9.8, 7.1, 4.8, 2.6, 1.2m
Sea and ground surface temperature at 8.4m
Sea water temperature within the sea surface layer
Ground heat flux on the bottom of the tower.
RESULTs
Solar radiation flux (Ssolar):
Ssolar = 1000 W m-2 at noon on clear day
daily mean Ssolar = 300 W m-2
Reflective radiation flux (Sref):
Sref = 0.2Ssolar, measured albedo (?) is around 0.2
Use empirical value of ??0.1 for sea surface.
(??0.06~0.07, cf. Budiko, 1956)
Atmospheric radiation flux (Latm):
Latm = 400~460 W m-2
daily mean Latm = 430 W m-2
Sea surface emitting radiation flux (Lsea):
Radiative temperature = Water temperature
Sea surface temperature Tsea = 30 oC
Lsea = 360 W m-2
Net radiation (RNET):
RNET > 900 W m-2 at noon on clear day.
RNET < 0 W m-2 during night.
daily mean RNET = 240 W m-2
Sensible heat flux, SHF, (H):
H = 5~10 W m-2
Latent heat flux, LHF, (?E):
?E = 50~100 W m-2
DISCUSSION
Fetch
The observation period can be divided in to three Phases according to the wind condition;
(1) 15AUG~17AUG
Wind direction: South-east
CO2 and momentum flux: Large
The wind might come from the land surface.
(2) 18AUG~23AUG
Wind direction: North
CO2 and momentum flux: Stable
The wind might come from the sea surface.
(3) 18AUG~23AUG
Wind direction: mainly South, but unstable
CO2 and momentum flux: Unstable
The wind might come from both surface.
Bulk transfer analysis
Measured bulk transfer coefficient;
for sensible heat: much larger than empirical value,
for latent heat: almost agree with empirical value.
Eddy fluxes
Measured sensible heat flux can be affected by large sensible heat flux from ground surface, which is driven by high ground surface temperature (sometimes, more than 60 oC). --->overestimated?
Measured latent heat flux also might be affected by the smaller ground surface flux.--->underestimated?
APPENDIX
Energy balance equations
(1) within the sea surface layer:
Latm - Lsea + Hw = H + ?E
Hw: upward heat flux within the surface layer
(2) under the sea surface layer:
Ssolar - Sref = Hw + G
G: downward and lateral heat flux
Bulk transfer equations
H = ?CPCHU (Tsea - T)
?E = ?CEU (qSAT(Tsea) - q)
CH = CE = (1.1~1.2) x 10-3 (cf. Kondo, 1994)
?: atmospheric density
CP: specific heat at constant pressure
?: latent heat for evaporation
U: wind speed at 10m
T: air temperature at 10m
q: vapor density at 10m
qSAT(T, s) = (1 - 0.000537s) qSAT(T, 0)
s: salinity (ppt), actually 35ppt
Eddy covariance method
H = ?CP wT = ?CP
?E = ? wq = ?
w: vertical wind velocity