Measurements and methods Directory UMM :Data Elmu:jurnal:A:Agricultural & Forest Meterology:Vol102Issue2-3May2000:
116 D. Amarakoon et al. Agricultural and Forest Meteorology 102 2000 113–124
Table 1 The number of data collection days and the daytime 07:00–18:00 hours average environmental conditions under which the experiments
were performed during August to September of 1989, January to February of 1990 and January to February of 1994 Parameter
a
August–September 1989 January–February 1990
January–February 1994 N
26 31
32 R
s
W m
− 2
170.0–890.0 90.0–750.0
73.5–629.6 R
n
W m
− 2
74.2–564.2 37.1–473.0
6.7–394.0 θ
◦
C 25.3–32.1
20.7–30.0 22.9–28.3
u m s
− 1
0.6–4.4 0.5–5.2
0.8–3.2 δ
e mb
2.08–15.6 6.9–18.9
7.3–15.6 Average RH
81 63
79 L
m −
0.014 to −275 0.004 −
4 to −348 2.7 −
6 to –151 0.04
a
Definitions of the parameters R
s
, R
n
, θ , u, and RH are the same as in Table 2. N=number of data collection days and δe=vapor pressure deficit. The relative humidity shown is the ratio, vapor pressure measured at 1.5 m to saturation vapor pressure calculated using
the result of Lowe 1977. The measured average relative humidity in 1994 was 73. L is the Monin–Obukhov length estimated by the method outlined in Appendix A. The positive values of L within parentheses are for stable situations in the morning at 07:00 hours or in
the late afternoon at 17:00 hours. 75 of the L values were in the range −150L0 m. The values of all the quantities given are hourly average values, except N. Hourly average values refer to averages for each hour between 07:00 and 18:00 hours.
upwind and 30 m downwind, followed by an embank- ment about 10 m high. The wind was primarily from
the south. The surfaces at both sites were covered with grass of Bahamian variety of average height 10 cm
and were irrigated regularly, three times a week, to ensure that there was enough water to evaporate. The
average of the ratio, lmeasuredl
eq
, was 1.17 based on hourly values of the fluxes. The top soil surface at
both sites was mainly loam. The data collection period at Mona was January to February of 1994, and the
periods at St. Catherine were August to September of 1989 and January to February of 1990. The daytime
environmental conditions during the three periods and the number of data collection days are given in
Table 1. The atmosphere was predominantly unsta-
Table 2 Parameters measured, instruments used and the height of measurements in this study, during the periods: August to September of 1989,
January to February of 1990 and January to February of 1994 Parameter
a
Instrument Height of measurement m
R
n
Fritschen Model 3032 and Swissteco type S-1 Model CH9463 net radiometers 2.0
R
s
Li-Cor Inc. Model LI-200SZC pyranometer 2.0
RH and θ
b
Campbell Scientific Inc. Model 207 temperature and relative humidity probe 2.0
e and θ
c
Campbell Scientific Inc. Dew-10 series Bowen ratio system 0.5 and 1.5
u MET 1 cup anemometer system
2.0 G
s
Radiation and Energy Balance Systems REBS, Inc. HFT-1 series heat flux plates −
0.10 θ
s
Thermocouples −
0.05
a
R
n
= net radiation, R
s
= global short-wave radiation, RH=relative humidity, θ =air temperature, e=vapor pressure, u=wind speed,
G
s
= soil heat flux at 0.10 m below the surface, θ
s
= soil temperature at 0.05 m below the surface.
b
RH measured only in January–February of 1994.
c
Bowen ratio system provided measurements of e and θ at 0.5 m and 1.5 m.
ble, as indicated by the estimated values of Monin– Obukhov length L. A few early morning and late
afternoon L values depicted stable L0 or neutral |L|150 m conditions. The method of estimation of
L
is given in Appendix A. The atmospheric instability observed in this work agrees with the other studies
Hsu, 1982; Chen et al., 1990 on tropical atmospheric instability.