Hirohiko Ishikawa

Kyoto University, Kioto, Kyoto, Japan

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Publications (51)89.05 Total impact

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    ABSTRACT: The Fukushima nuclear accident (March 11, 2011) caused the widespread contamination of Japan by direct deposition of airborne radionuclides. Analysis of weekly air filters revealed sporadic releases of radionuclides long after the Fukushima Daiichi reactors have been stabilized. One major discharge was observed in August 2013 in monitoring stations north of the Fukushima Daiichi nuclear power plant (FDNPP). During this event, an air monitoring station in this previously scarcely contaminated area suddenly reported (137)Cs activity levels that were 30-fold above the background. Together with atmospheric dispersion and deposition simulation, radionuclide analysis in soil indicated that debris removal operations conducted on the FDNPP site on August 19, 2013 are likely to be responsible for this late release of radionuclides. One soil sample in the center of the simulated plume exhibited a high (90)Sr contamination (78±8 Bq kg(-1)) as well as a high (90)Sr/(137)Cs ratio (0.04); both phenomena have usually been observed only in very close vicinity around the FDNPP. We estimate that through the resuspension of highly contaminated particles in the course of these earthmoving operations, a gross (137)Cs activity of ca. 2.8×10(11)Bq has been released.
    No preview · Article · Oct 2015 · Environmental Science & Technology
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    Yuichiro Oku · Jun Yoshino · Tetsuya Takemi · Hirohiko Ishikawa
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    ABSTRACT: Typhoon Talas (2011) caused extensive damage through landslides on the Kii Peninsula, Japan, in September 2011. The purpose of the present study is to quantitatively describe the potential for the occurrence of heavy rainfall-induced disasters if the typhoon track perturbs slightly or the typhoon intensifies. Regarding to the consideration of the track displacement of the typhoon, a procedure is proposed to generate different typhoon tracks perturbed from the original track of the typhoon. In this procedure, the position of a typhoon is artificially shifted at a certain time before landing in a physically consistent manner by applying potential vorticity inversion (PVI) methodology. After relocating the typhoon, the subsequent progress is simulated by a mesoscale meteorological model. Using the output, which consists of a set of realizations having different typhoon tracks, the worst-case scenario is discussed in terms of the soil water index (SWI) of the Kii Peninsula. The SWI is an indicator of the amount of water in soil that represents the hazard of landslide disasters. The maximum spatially averaged SWI is 1.10 times as large as that from the original typhoon track. Regarding the consideration of severer typhoon, the same method is used, but the intensity of the potential vorticity of a typhoon is artificially modified at the position instead of relocating potential vorticity to a different place. The maximum spatially averaged SWI is 1.28 times as large as that of the original typhoon intensity.
    Full-text · Article · Oct 2014
  • Weiqiang Ma · Yaoming Ma · Hirohiko Ishikawa
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    ABSTRACT: Evapotranspiration (ET) is a boundary condition for regional scale hydrological and climatological modeling. Spatial knowledge of land surface ET is of principal interest for environmental evaluation especially in semi-arid regions. The study used the Surface Energy Balance System (SEBS) model based on Advanced Spaceborne Thermal Emission and Reflection Radiometer (ASTER) remote sensing and field observations data that have been used and tested for deriving ET over the NamCo area in the Tibetan Plateau, located in the southwest of China. Two ASTER scenes were used for estimating the ET over the study area. To validate the proposed methodology, the ground-measured ET was compared to the ASTER derived ET values for the study area. The results show that the derived ET in different months over the study area is in good accordance with the in-situ data. The derived ET value over the study area is much closer to the field measurement; the RMSE is 0.7 mm/d. It is therefore concluded that the SEBS methodology is successful for the retrieval of ET using the ASTER and in-situ data over the study area.
    No preview · Article · Mar 2014 · Atmospheric Research
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    ABSTRACT: Radiation dose rates were evaluated in three areas neighboring a restricted area within a 20- to 50-km radius of the Fukushima Daiichi Nuclear Power Plant in August-September 2012 and projected to 2022 and 2062. Study participants wore personal dosimeters measuring external dose equivalents, almost entirely from deposited radionuclides (groundshine). External dose rate equivalents owing to the accident averaged 1.03, 2.75, and 1.66 mSv/y in the village of Kawauchi, the Tamano area of Soma, and the Haramachi area of Minamisoma, respectively. Internal dose rates estimated from dietary intake of radiocesium averaged 0.0058, 0.019, and 0.0088 mSv/y in Kawauchi, Tamano, and Haramachi, respectively. Dose rates from inhalation of resuspended radiocesium were lower than 0.001 mSv/y. In 2012, the average annual doses from radiocesium were close to the average background radiation exposure (2 mSv/y) in Japan. Accounting only for the physical decay of radiocesium, mean annual dose rates in 2022 were estimated as 0.31, 0.87, and 0.53 mSv/y in Kawauchi, Tamano, and Haramachi, respectively. The simple and conservative estimates are comparable with variations in the background dose, and unlikely to exceed the ordinary permissible dose rate (1 mSv/y) for the majority of the Fukushima population. Health risk assessment indicates that post-2012 doses will increase lifetime solid cancer, leukemia, and breast cancer incidences by 1.06%, 0.03% and 0.28% respectively, in Tamano. This assessment was derived from short-term observation with uncertainties and did not evaluate the first-year dose and radioiodine exposure. Nevertheless, this estimate provides perspective on the long-term radiation exposure levels in the three regions.
    No preview · Article · Feb 2014 · Proceedings of the National Academy of Sciences
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    ABSTRACT: Analysis of (137)Cs trapped in biomass in highly contaminated zones is crucial in predicting the long-term fate of (137)Cs following the explosion at the Fukushima Daiichi Nuclear Power Plant. We surveyed forest 20 to 50 km from the plant in July and September 2011 to evaluate (137)Cs trapped in biomass within 20 km of the plant. We determined the ambient dose rate and collected forest soils and twigs at 150 sampling points. Removability from the canopy was evaluated by washing leaves and branches with water and organic solvents. The biomass of forest canopy was then calculated. (137)Cs fallout was simulated with an atmospheric transport model. The modeled dose rate agreed with observations (n = 24) (r = 0.62, p < 0.01). Washing experiments demonstrated that unremovable portions accounted for 53.9% ± 6.4% of (137)Cs trapped by deciduous canopy (n = 4) and 59.3% ± 13.8% of (137)Cs trapped by evergreen canopy (n = 10). In total, it was estimated that 74.5 × 10(12) Bq was trapped by canopy in the forest within the no-go zone, with 44.2 × 10(12) Bq allocated to unremovable portions, and that 0.86% of the total release was trapped in biomass as of September 2011.
    No preview · Article · Jul 2013 · Environmental Science & Technology
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    Hirohiko Ishikawa · Yuichiro Oku · Sunmin Kim · Tetsuya Takemi · Jun Yoshino
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    ABSTRACT: The damage to society caused by tropical cyclones depends largely on the storm track relative to geography. A procedure is proposed to generate different typhoon tracks deviating from the original track of a given reference case. In this procedure, the position of a typhoon is artificially shifted at a certain time before landing in a physically consistent way by applying potential vorticity inversion methodology. After shifting the typhoon position, the subsequent progress is again simulated by a mesoscale weather model. The procedure is applied to a strong typhoon that emerged in a global warming experiment using an atmospheric general circulation model. Various realizations of typhoon landfall cases are generated. Using the output of a suite of realization of different tracks, the worst case scenario is discussed in terms of the river discharge in the Tone River basin, Japan. Copyright © 2013 John Wiley & Sons, Ltd.
    Full-text · Article · May 2013 · Hydrological Processes
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    Weiqiang Ma · Mohsin Hafeez · Umair Rabbani · Hirohiko Ishikawa · Yaoming Ma
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    ABSTRACT: h i g h l i g h t s < The idea of ET is of the most interesting for landeatmosphere interactions. < SEBS model for deriving ET over Coleambally Irrigation Area (CIA). < In-situ ET was compared to RS retrieved ET results. a b s t r a c t The idea of ground-based evapotranspiration (ET) is of the most interesting for landeatmosphere interactions, such as water-saving irrigation, the performance of irrigation systems, crop water deficit, drought mitigation strategies and accurate initialization of climate prediction models especially in arid and semiarid catchments where water shortage is a critical problem. The recent year's drought in Australia and concerns about climate change has prominent the need to manage water resources more sustainably especially in the Murrumbidgee catchment which utilizes bulk water for food security and production. This paper discusses the application of a Surface Energy Balance System (SEBS) model based on Landsat-5 TM data and field observations has been used and tested for deriving ET over Coleambally Irrigation Area (CIA), located in the southwest of NSW, Australia. 16 Landsat-5 TM scenes were selected covering the time period of 2009, 2010 and 2011 for estimating the actual ET in CIA. To do the validation the used methodology, the ground-measured ET was compared to the Landsat-5 TM retrieved actual ET results for CIA. The derived ET value over CIA is much closer to the field measurement. From the remote sensing results and observations, the root mean square error (RMSE) is 0.74 and the mean APD is 7.5%. The derived satellite remote sensing values belong to reasonable range.
    Full-text · Article · May 2012 · Atmospheric Environment
  • Weiqiang Ma · Mohsin Hafeez · Hirohiko Ishikawa · Yaoming Ma
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    ABSTRACT: Spatial knowledge of land surface evapotranspiration (ET) is of prime interest for environmental applications, such as optimizing irrigation water use, irrigation system performance, crop water deficit, drought mitigation strategies, and accurate initialization of climate prediction models especially in arid and semiarid catchments where water shortage is a critical problem. The recent drought in Australia and concerns about climate change have highlighted the need to manage water resources more sustainably especially in the Murrumbidgee catchment which utilizes bulk water for food production. This study deals with the application of a Surface Energy Balance System (SEBS) algorithm based on Advanced Spaceborne Thermal Emission and Reflection radiometer (ASTER) data and field observations has been proposed and tested for deriving ET over Coleambally Irrigation Area, located in the southwest of NSW, Australia. We have used 12 ASTER scenes covering the time period of 2002, 2003, 2004, 2005, 2006, and 2009 for estimating the actual ET over the study area. To validate the proposed methodology, the ground-measured ET was compared to the ASTER-derived actual ET values for the study area. The derived ET value over the study area is much closer to the field measurement. From the remote sensing results and observations, the root mean square error is 0.89 and the mean absolute percentage difference is 2.87 %, which demonstrate the reasonability of SEBS ET estimation for the study area.
    No preview · Article · May 2012 · Theoretical and Applied Climatology
  • Tetsuya Takemi · Syohei Nomura · Yuichiro Oku · Hirohiko Ishikawa
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    ABSTRACT: Understanding and forecasting of summertime afternoon precipitation due to rapidly developing cumulonimbus clouds without any significant synoptic-scale influences are important to prevent and mitigate the induced disasters. Future changes in the behavior of such precipitation events have recently gained scientific and societal interests. This study investigates the environmental stability for afternoon precipitation that develops under synoptically undisturbed conditions in summer by using the outputs of 20-km-mesh, super-high-resolution atmospheric general circulation model (GCM) simulations for a present, a near-future, and a future climate under global warming with the Intergovernmental Panel on Climate Change A1B emission scenario. The Kanto Plain was chosen as the analysis area. After verifying the usefulness of the GCM present-climate outputs with observations and gridded mesoscale analyses, we examine the future changes in the environmental stability for the afternoon precipitation by conducting statistical analyses. In the future climates, temperature lapse rate decreased in the lower troposphere, while water vapor mixing ratio increased throughout the deep troposphere. The changes in the temperature and moisture profiles resulted in the increase in both precipitable water vapor and convective available potential energy. These projected changes will be enhanced with the future period. Furthermore, the statistical analyses for the differences of the stability parameters between no-rain and rain days under the synoptically undisturbed condition in each simulated climate period indicated that the representations of the stability parameters that distinguish no-rain and rain events are basically unchanged between the present and the future climates. This result suggests that the environmental characteristics favorable for afternoon precipitation in the synoptically undisturbed environments will not change under global warming.
    No preview · Article · Feb 2012 · Journal of the Meteorological Society of Japan
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    ABSTRACT: This study aims to estimate the ecological exposure of adult residents of Fukushima Prefecture to ¹³⁴cesium (Cs) and ¹³⁷Cs through ingestion and inhalation between July 2 and July 8, 2011. Fifty-five sets of meals with tap water, each representing one person's daily intake, were purchased in local towns in Fukushima Prefecture. Locally produced cow's milk (21 samples) and vegetables (43 samples) were also purchased. In parallel, air sampling was conducted at 12 different sites using a high-volume sampler. Nineteen sets of control meals were collected in Kyoto in July 2011. ¹³⁴Cs and ¹³⁷Cs levels in the samples were measured using a germanium detector. Radioactivity was detected in 36 of the 55 sample meals from Fukushima, compared with one of 19 controls from Kyoto. The median estimated dose level (μSv/year) was 3.0, ranging from not detectable to 83.1. None of the cow's milk (21) or vegetable (49) samples showed levels of contamination above the current recommended limits (Bq/kg) of 200 for milk and 500 for vegetables. The total effective dose levels by inhalation were estimated to be <3 μSv/year at nine locations, but samples at three other locations close to the edge of the 20-km radius from the crippled nuclear power plant showed higher levels of contamination (μSv/year): 14.7 at Iitate, 76.9 at Namie, and 27.7 at Katsurao. Levels of exposure to ¹³⁴Cs and ¹³⁷Cs in Fukushima by ingestion and inhalation are discernible, but generally within recommended limits.
    Full-text · Article · Nov 2011 · Environmental Health and Preventive Medicine
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    ABSTRACT: Environmental ecological modeling (EEM), which unifies models simulating transport of chemicals and exposure of humans to chemicals, was used to simulate long-term trends of female adult human blood lead levels (BLLs) and historical exposure to the atmospheric lead in four East Asian countries: Japan, Korea, China, and Vietnam. Anthropogenic lead emissions to the atmosphere in Vietnam were estimated from energy statistics to be 1931 t yr(-1). Calculated BLLs generally agreed with those observed in samples collected in these countries as the error factors were less than 2. The model results revealed that BLLs decreased significantly in Tokyo (by 58%) and Seoul (by 45%) in recent decades and confirmed the effects of efforts to reduce environmental lead in Japan and Korea. The model results also revealed that BLLs in Beijing did not decrease in this decade as much as in Tokyo and Seoul, despite the phasing out of leaded gasoline, and that the contribution from the atmospheric component was increasing (43% in 2009). Finally, we applied EEM to simulate BLLs of children in Hanoi. The probability of children having BLLs greater than 50 μg L(-1) was 7.5%, which was greater than those observed in developed countries.
    Full-text · Article · Feb 2011 · Environmental Science & Technology
  • Yuichiro Oku · Mizuo Kajino · Hirohiko Ishikawa
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    ABSTRACT: The algorithm used to retrieve the cloud effective particle radius from the 3.7 μm band was adapted to the corresponding channel of the Japanese Advanced Meteorological Imager (JAMI) flown on board the Multi-functional Transport Satellite (MTSAT) geostationary platform. Snapshot comparisons with spatially well-resolved retrievals from the MODerate resolution Imaging Spectrometer (MODIS) instruments flown on the Terra polar platforms show qualitative agreement with MTSAT retrievals. The results of analysing daytime variation from eastern Asia to the northwest Pacific Ocean show that, not only is the effective particle radius smaller in continental clouds than in maritime clouds, but the daytime amplitude of the effective particle radius is also greater in continental clouds than in maritime clouds, where the effective particle radius value is approximately constant.
    No preview · Article · Oct 2010 · International Journal of Remote Sensing
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    Tamon Niisoe · Kouji H Harada · Hirohiko Ishikawa · Akio Koizumi
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    ABSTRACT: A publicly available atmospheric transport model, the Weather Research and Forecasting Chemistry Model ( http://ruc.noaa.gov/wrf/WG11/ ), was used to simulate atmospheric perfluorooctanoic acid (PFOA) and perfluorooctanoate (PFO) emitted from a point source in the Osaka urban area (also known as Keihanshin), Japan. The time period of the simulation was from 1983 to 2008. The modeled air concentrations were highly correlated (r = 0.91) with the observed air concentrations. Intake levels by inhalation of simulated air concentrations and through the gastrointestinal tract as estimated by the food duplicate method were input to a pharmacokinetic model of the human body to simulate serum concentrations of PFOA and PFO (PFO(A)). For validation of the atmospheric model, simulated values were compared with those observed in serum samples. The simulated values generally agreed with those observed in serum samples from residents of the Keihanshin area (r = 0.93). It was confirmed that the atmospheric model was generally capable of projecting features of atmospheric PFO(A) as well as serum concentrations of PFO(A) in this case. The results indicated a dominant contribution of the atmospheric component to serum PFO(A) in humans near the point source in the Keihanshin area. In 2008, that contribution was about 70%.
    Full-text · Article · Oct 2010 · Environmental Science & Technology
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    Yuichiro Oku · Hirohiko Ishikawa

    Preview · Article · May 2010
  • Yuichiro Oku · Tetsuya Takemi · Hirohiko Ishikawa · Sachie Kanada · Masuo Nakano
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    ABSTRACT: The representations of extreme weather during the landfall of Typhoon Songda (2004) in regional simulations at 1-km resolution are described and compared for two cloud-resolving models: Non-hydrostatic Model (NHM) and the Weather Research and Forecasting model (WRF). Both models, using the same 5-km-mesh outputs from NHM as their initial and boundary conditions, successfully reproduced the observed typhoon track and intensity. The comparison of surface winds indicated that WRF evaluates more enhanced extremes than NHM; on the other hand, the representations of rainfalls indicated that the extremes of hourly and accumulated rainfalls simulated by the two models are evaluated differently. Slight differences in the model topography between the two models, though produced by the same terrain dataset, were shown to significantly affect the representations of the extremes in each model. It should be recognized that not only the differences in model numerics and physics but also slight changes in the reproduction of topography induce differences in the representations of extreme weather.
    No preview · Article · Jan 2010 · Hydrological Research Letters
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    ABSTRACT: Parameterization of turbulent flux from bare-soil and undercanopy surfaces is imperative for modeling land–atmosphere interactions in arid and semiarid regions, where flux from the ground is dominant or comparable to canopy-sourced flux. This paper presents the major characteristics of turbulent flux transfers over seven bare-soil surfaces. These sites are located in arid, semiarid, and semihumid regions in Asia and represent a variety of conditions for aerodynamic roughness length (z 0m ; from 1 to 10 mm) and sensible heat flux (from 50 to 400 W m 2). For each site, parameter kB 1 [ln(z 0m /z 0h), where z 0h is the thermal roughness length] exhibits clear diurnal variations with higher values during the day and lower values at night. Mean values of z 0h for the individual sites do not change significantly with z 0m , resulting in kB 1 increasing with z 0m , and thus the momentum transfer coefficient increases faster than the heat transfer coefficient with z 0m . The term kB 1 often becomes negative at night for relatively smooth surfaces (z 0m 1 mm), indicating that the widely accepted excess resistance for heat transfer can be negative, which cannot be explained by current theories for aerodynamically rough surfaces. Last, several kB 1 schemes are evaluated using the same datasets. The results indicate that a scheme that can reproduce the diurnal variation of kB 1 generally performs better than schemes that cannot.
    Full-text · Article · Mar 2008 · Journal of Applied Meteorology and Climatology
  • Yaoming Ma · Tandong Yao · Hirohiko Ishikawa · Toshio Koike
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    ABSTRACT: The energy and water cycles over the Tibetan Plateau play an important role in the Asian monsoon system, which in turn is a major component of both the energy and water cycles of the global climate system. Using field observational data observed from the GAME/Tibet (Global Energy and Water cycle Experiment [GEWEX] Asian Monsoon Experiment on the Tibetan Plateau) and the CAMP/Tibet (Coordinated Enhanced Observing Period [CEOP] Asia-Australia Monsoon Project [CAMP] on the Tibetan Plateau), some results of the local surface energy partitioning (diurnal variation and inter-monthly variation etc.) are presented in this paper. The study on the regional surface energy partitioning is of paramount importance over the heterogeneous landscape of the Tibetan Plateau and is also one of the main scientific objectives of the GAME/Tibet and the CAMP/Tibet. Therefore, the regional distributions and their inter-monthly variations of surface heat fluxes (net radiation flux, soil heat flux, sensible heat flux and latent heat flux) are also derived by combining NOAA-14/AVHRR data and Landsat-7 ETM data with field observations. The derived results are validated with field observation, and by using the methods proposed in this study it shows that the derived regional distributions and their inter-monthly variations of land surface heat fluxes are reasonable. Further improvement of the method and its application field are also discussed. In order to bring up to scale the land surface heat fluxes to the whole Tibetan Plateau area, the Institute of Tibetan Plateau Research (ITP) of the Chinese Academy of Sciences (CAS) is establishing a Monitoring and Research Platform (MORP) for the study of land surface and atmospheric processes on the Tibetan Plateau. The establishing and monitoring plans of long-term scale (5-10 years) of the MORP are also introduced here.
    No preview · Chapter · Dec 2007
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    Yaoming Ma · Hui Tian · Hirohiko Ishikawa · Ryohji Ohba · Hiromasa Ueda · Jun Wen
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    ABSTRACT: In this study, a parameterization method based on Landsat-7 Enhanced Thematic Mapper (ETM) data and field observations is presented and tested for deriving the regional land surface variables, vegetation variables and land surface heat fluxes over a heterogeneous landscape. As a case study, the method and two Landsat-7 ETM images are applied to the Jiddah area of Saudi Arabia. The regional distribution maps of surface reflectance, normalized difference vegetation index, modified soil adjusted vegetation index (MSAVI), vegetation coverage, leaf area index, surface temperature, net radiation flux, soil heat flux, sensible heat flux and latent heat flux have been determined over the Jiddah area. The derived results have been validated by using the ‘ground truth’. The results show that the more reasonable regional distributions of land surface variables (surface reflectance, surface temperature), vegetation variables (MSAVI and vegetation coverage), net radiation, soil heat flux and sensible heat flux can be obtained by using the method proposed in this study. Further improvement of the method is also discussed. Copyright © 2006 John Wiley & Sons, Ltd.
    Full-text · Article · Jul 2007 · Hydrological Processes
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    ABSTRACT: This study proposed a parameterization methodology based on Landsat-7 ETM data and field observations and tested it for deriving an evaporative fraction (EF) over a heterogeneous landscape. As a case study, the methodology was applied to the experimental area of CAMP/Tibet located on the central Tibetan Plateau. Four scenes of Landsat-7 ETM data were used in the study. Scenes of 9 June 2002 and 28 August 2002 were selected as case examples of summer and autumn, respectively; the scene of 2 December 2002 was selected as a winter case; and 24 March 2003 was selected as a spring case (or pre-monsoon period). To validate the proposed methodology, the Landsat-7 ETM derived EFs were compared to ground-measured values in four different months that spanned a wide range of surface conditions and surface features. This comparison revealed that the predictions were in good accordance with the ground measurements with absolute percent differences of less than 9.5%. It was concluded that the proposed methodology successfu11y facilitates the retrieval of EF using Landsat-7 ETM data and field observations over the study area
    Full-text · Article · Mar 2007 · Journal of the Meteorological Society of Japan
  • Yuichiro Oku · Hirohiko Ishikawa · Zhongbo Su
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    ABSTRACT: A Surface Energy Balance System (SEBS) originally developed for the NOAA Advanced Very High Resolution Radiometer was applied to Geostationary Meteorological Satellite (GMS)-5 Visible/Infrared Spin-Scan Radiometer data that were supplemented with other meteorological data. GMS-5, which is a geostationary satellite, recorded continuous hourly information. Surface temperatures obtained from the GMS-5 data were entered into SEBS to estimate the hourly regional distribution of the surface heat fluxes over the Tibetan Plateau. The estimated fluxes are verified by using corresponding field observations. The diurnal cycle of estimated fluxes agreed well with the field measurements. For example, the diurnal range of the estimated sensible heat flux decreases from June to August. This reflects the change of dry to wet surface characteristics resulting from frequent precipitation during the summer monsoon. Over the Tibetan Plateau, the diurnal range of the surface temperature is as large as the annual range, so that the resultant sensible heat flux has a large diurnal variation. Thus, the hourly estimation based on the GMS data may contribute to a better understanding of the land surface-atmosphere interaction in this critical area.
    No preview · Article · Feb 2007 · Journal of Applied Meteorology and Climatology