Surface Heat Balance using Flux Measurement Arrayduring Catch A Plume by SATs (CAPS) IOP∗ Sachinobu Ishida1 , Kenji Tanaka2 , Atsushi Higuchi3 , Ichiro Tamagawa4 , Dai Matsushima5and CAPS2002-2003 observation group(1: Dept. of Earth and Environmental Sci., Hirosaki University, 2: DPRI, Kyoto University,
3: HyARC, Nagoya University, 4: River Basin Research Center, Gifu University
and 5: Graduate School of Science, Tohoku University )∗ Dept. of Earth and Environmental Sci., Hirosaki University, Bunkyo-cho 3, Hirosaki, 036-8561, Japan.

e-mail: ishida@cc.hirosaki-u.ac.jp

Abstract
The intensive meteorological observation, CAPS (Catch A Plume by SATs), was carried out twice over postharvest
paddy field in northern Shiga prefecture, JAPAN in 2002, 2003. The objective of this project is to understand 1) thedistribution of the sensible heat flux over homogeneous surface, and 2) it’s influence for surface heat balance; 3) thebehavior of the plume, which affects the temporal and spatial distribution of the sensible heat flux. The SATs array andthe scintillometers were installed to measure the heterogeneity of the heat flux, with other instruments to complete thesurface energy balance. Also surface temperature images were taken by the infrared camera from airplane. And theupper ABL sounding was held using a radio sonde, two SODARs and a lidar. This study is focused on the objective 1)
and 2). In CAPS2002, the distance of each SAT was O(100m), and the array was extended 500×1500m horizontallyusing 16 SATs. The heat balance closure ratio was about 60%. The difference between max. and min. sensible heat
flux was almost equal to the random error, and was about 30% of mean flux (77W/m2 ) during 9-15 local time in clear
condition, and the difference seems to be correspond to the surface temperature distribution. But this difference still
does not explain the absence of heat. In CAPS2003, the distance of each SAT was O(10m), and the array was extended
100×200m horizontally using 17 SATs. The difference ratio of the sensible heat flux was smaller than CAPS2002. And
the heat balance closure ratio was about 100% by averaging data of the multiple measurement sites.
Keyword: heat balance, imbalance, flux measurement array, CAPS.

1. Introduction
Many projects, such as GAME, have been held and are inprogress, to understand the land-atmosphere interaction and theenergy and water cycles, meanwhile there have been many problems related to the ABL observation as follows:
The energy (heat) imbalance: the underestimation of the turbulent energy (H + lE) flux compared to the forcing energy(Rn − G).

2003, the distance of each SAT was O(100m) and O(10m) respectively. The footprints of each site in CAPS2002 were independent whereas the ones in CAPS2003 could be overlapped.
Thus, the dynamic structure throughout scale from 10m to 1km
will be resolved by using the data. In this paper, the distributionof the sensible heat flux and the heat balance is analyzed.

2. Observation

Footprint: the source area or the distribution of it’s contribution
ratio of turbulent flux.
Stationary convection (plume): although over the homogeneous surface, buoyant flow tends to occur in the same area.
Averaging time: if there is long period turbulence, too short averaging time to estimate turbulent flux would provoke underestimation.
The energy imbalance would be caused by the latter three problems.
The Flux Enthusiasts Party consists of those who are interested in such problems and the turbulence in ABL (Toda et al.,2000). The intensive integrated ABL observation has been carried out by together with the Flux Enthusiasts Party and the Lake
Biwa Project at the paddy field site of the Lake Biwa Project.
The Lake Biwa Project has been developed and proceeded bya Japanese group for investigating the hydrological cycle nearland surface. This observation was called CAPS (Catch A Plumeby SATs; SAT is the Sonic Anemometer-Thermometer) because
over 16 SATs were used in order to understand the dynamicstructure of the plume and the convection in SBL.
The observation has been carried out twice in 2002
(CAPS2002) and 2003 (CAPS2003) autumn. In CAPS2002 andFig. 1: Turbulent sensors’ distribution map of CAPS2002,
2003. (Right) CAPS2002: Legend is indicated in map.
(Left) CAPS2003: The line between N shows scintillometer path. +: SAT site (C, S3, N3: 3 heights; C, S1, N1, E1,
W1: with water vapor sensor), ◦: fine wire thermocouplesite.
The intensive observations have been performed during
November 9 to 22, 2002 and October 1 to 10, 2003. Both periods were after harvest because the homogeneous surface and thegreater sensible heat flux conditions were expected during these3.1. CAPS2002
Only at C4 site, all terms of the heat balance equation weremeasured successfully. But the imbalance heat flux was up to
100Wm−2 around the noon (Fig. 2), and the closure ratio was60%. The heat imbalance of CAPS2002 might depend on thedistribution of the surface conditions. The surface of C4 site wasdark and wet. The albedo of this site was 5∼10% lower thanthe other sites, that means the net shortwave radiation input was
nearly 55Wm−2 lower around C4 site because the maximum incoming insolation was 550Wm−2 . And the maximum differenceof the surface temperature was about 2 ˚C in the observation region (Fig. 3). It might influence G, H smaller and lE larger.
All of these factors could make the local heat imbalance, butthey don’t explain all of the maximum imbalance (100Wm−2 )explicitly.
150–2(W m )periods. The site was located near Lake Biwa in northern Shiga
prefecture, JAPAN (Fig. 1). Prevailing wind direction was parallel to the paths between paddy fields, southerly (lake breeze) in
daytime and northerly (land breeze) in nighttime under clear sky
conditions. Fig. 1 shows the distribution of turbulent sensors.
These distribution were oriented parallel to the prevailing winddirections.
In CAPS2002, there were 15 SAT sites using 17 SATs in orderto measure the heterogeneity of the heat flux. At every site, theinstallation height of SATs were about 2.5m. 4 of them (C1, C2,C4, C5 site) were with the open-path infrared gas analyzers, andSATs were installed at 3 heights (1.00, 2.45, 5.90m) especially atC4 site. To complete the rest term of the heat balance, other sensors were installed at C sites, only the sensors of C4 site workedwell. The measurement area was extended 500×1500m horizontally. Also surface temperature images were taken by the infrared
camera from airplane in November 17, 19, 20 under clear sky
conditions. And the upper ABL sounding was held using a radio
sonde and two SODARs. Details were described in Tamagawa
et al.(2004).
In CAPS2003, there were 11 SAT sites using 16 SATs tomake SAT array. Common SAT installation height was 2.5m
the same as CAPS2002. C, S1, N1, E1, W1 sites were with theopen-path infrared gas analyzers, and SATs were installed at 3heights (1.25, 2.50, 5.00m) at C, S3, N3 sites. The most different point from CAPS2002 was that the measurement area wasconcentrated about 100×200m, centered at C2 site (called intensive paddy field) of CAPS2002. Since each tract of paddy
field is about 30m width and 100m length, multiple SATs werein the same tract. Fine wire thermocouples were used to detect
the passing plume near the surface. Surface temperature distribution was measured manually by the two infrared thermometer.
The upper ABL sounding was held using a radio sonde, two SODARs and a doppler lidar.
The SATs used in CAPS were composed of 10 sets of DA-600(Kaijo), more than 2 sets of 1210R3 (Gill) and a set of SAT-550(Kaijo) and other types. Especially, DA-600 and 1210R3 wereconfirmed that their outputs were almost the same (within 10%difference) sensible heat flux by the eddy correlation method(Ishida et al., 2004).

Re(1.0)Re(2.5)Re(6.0)100
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Date of November, 2002

2021Fig. 2: The residual term of the heat balance of CAPS2002
at C4 site (3 heights; 1.0, 2.5, 6.0m).
Infrared Thermometer Image (2002, Nov.17, 11:35-11:58)

s0

S1084s2

C17035˚ 29' 40"N

s1S2

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s6S679s57235˚ 29' 20"NS5c467

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9 10 11 12 13 14 15 16 17 18 19 20 21 22 23Surface Temperature [oC]

Fig. 3: Distribution map of the average sensible heat flux for
9 to 15JST, Nov. 17, 19, 20, 2002 (right), and the surface
temperature for 11:35 to 11:58JST, Nov. 17, 2002(left).

3. Heat Balance
Each term of the heat balance equation:
Rn − G = H + lE
was measured independently and averaged for each hour. The
net radiation Rn was measured by the pyranometers and the infrared radiometers. Since both observations were performed inless than 2km horizontal scale, downward radiation was homogeneous in the area. Upward radiation, however, depended on
the surface conditions such as the albedo and the surface temperature. The soil heat flux G was measured by the heat plates.
And the sensible and the latent heat flux H, lE was measured by
the SATs and the infrared gas analyzers (e.g. LI-7500, Li-Cor).
After the simple calibration of the absolute humidity a (Ishida etal., 2004) and the double axis rotations (w = 0), the eddy correlation method (H = c p ρ w0 T 0 , lE = lw0 a0 ) was applied. In thispaper, the heat balance closure ratio is defined as the ratio of theleft term to the right term of the heat balance equation.

Fig. 3 shows the distribution map of the sensible heat flux
and the surface temperature. The surface temperature was measured by the infrared camera (Inframatics, MODEL740), andmade calibration and correction of the geometry, the viewing
angle and the medium atmosphere, then combined by the multiple shot. The difference of the sensible heat flux between eachsite was almost equal to the random error, and was about 30%
of mean flux (77W/m2 ) during 9-15 local time under clear conditions. The difference seems to be correspond to the surface
temperature distribution.
Flux footprint analyses of Kormann and Meixner (2001) wereapplied to CAPS2002. Fig. 4 shows the footprint areas ofeach site. The footprint areas were spread northward, because
northerly wind was blowing at that time. However each shapes
were different by the influence of the local wind distribution.
The SATs were installed 3 heights at C4 site, the footprint areaof the highest SAT was larger. Fig. 5 shows the relationship between U(Ts − Ta ) and the normalized sensible heat flux. Ts wascalculated by the surface temperature in the footprint area. Thesensible heat flux was normalized by the bulk coefficient for draginfluenced by the roughness length at each site. The normalized
sensible heat flux was correlated with the product of the temperature difference between the surface and the air Ts − Ta and thewind speed U. The slope of the data means the bulk coefficientfor heat CH , which was almost unity through unstable conditions.
These results suggest that local sensible heat flux was determinedby the bulk relation of U(Ts − Ta ) in the footprint area.

horizontal grids and 80 vertical grids in which the finest resolution was 10m at the lowest grid. The simulation was started with
the initial condition at 9JST, Nov. 17, 2002, and calculated for 3hours (until 12JST). The sensible heat flux at the lowest grid wascalculated by the bulk method. The simulated sensible heat flux
was shown in Fig. 6. The structure of the plume seems to havea few hundred meters scale, and exists statically. And the amplitude of the sensible heat flux difference was consistent with theobservation (Fig. 3).

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Fig. 6: Distribution map of sensible heat flux simulatedby LES using boundary condition of 11-12JST, Nov. 17,CAPS2002.
Fig. 4: Footprint areas of the sensible heat flux of each SAT
site. 13JST, Nov. 19, CAPS2002.

Fig. 5: Relationship between U(Ts −Ta ) and the normalized
sensible heat flux in CAPS2002.
Large Eddy Simulation (LES/CReSS: Cloud Resolving StormSimulator) was performed under the same conditions ofCAPS2002, except for the homogeneous surface boundary conditions, z0 = 0.017m, albedo = 0.2, β = 0.2. CReSS is nonhydrostatic mesoscale model with cloud physics scheme. LES
is adopted for the one-and-a-half order turbulence closure to resolve plumes sufficiently. The modeled domain was 4×4km inhorizontal width and 1.6km in height with 40m resolution 100

3.2. CAPS2003
In order to measure greater spatial difference of the sensible heat, CAPS2003 was carried out 1 month earlier thanCAPS2002. So the maximum net insolation was 50Wm−2larger, and the surface temperature was 10 ˚C higher thanCAPS2002. Since the observation region was smaller, the difference of the upward shortwave and longwave radiation wassmaller. The maximum difference of the soil heat flux G was50Wm−2 . Thus the surface conditions must have been more homogeneous than CAPS2002. The difference ratio of the sensible
heat flux was a little smaller than CAPS2002 (Fig. 7), and was
almost equal to the random error. The footprint analysis should
be applied to CAPS2003 in future to understand what influences
the difference of the sensible heat flux.
The heat balance was roughly closed in CAPS2002; the average closure ratio was 100% whereas the deviation was up to100Wm−2 (Fig. 8). These results suggests that the heat balance
would be closed using the data measured at multiple points underthermally homogeneous surface conditions.

4. Conclusion
The heat imbalance is likely occurred by the one point observation. Followings are possible reasons:• There are slight heterogeneity of the thermal surface conditions; albedo, the surface wetness and temperature, evenon apparently homogeneous surface.
• The spatial difference of the turbulent heat flux is deter-mined by the local difference of the surface temperature
and wind speed caused by the plume in a few hundred meter scale.

n3142

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Fig. 7: Distribution map of daytime average sensible heatflux. 9 to 15JST, Oct. 10, 11, 12, CAPS2003.

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H+lE=Rn-G

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Fig. 8: Heat balance of C, N1, E1 site in CAPS2003. The
data of net radiation at S3 site was used.
ACKNOWLEDGMENT. CReSS, developed by Prof. K. Tsubokiof HyARC, Nagoya University and Dr. A. Kashiwabara of RIST,
was used in this paper.

References
Ishida et al., Journal of Japan Society of Hydrology & Water
Resources, 17, 43–60, 2004.
Kormann and Meixner, BLM, 99, 207–224, 2001.
Tamagawa et al., Journal of Japan Society of Hydrology & Water Resources, 17, 392–400, 2004.
Toda et al., Journal of Japan Society of Hydrology & Water Resources, 13, 396–405, 2000.