Numerical Study of Impacts of Soil Moisture on the Diurnal and Seasonal Cycles of Sensible/Latent Heat Fluxes over Semi-arid Region

The semi-arid regions, as climatic and ecosystem transitional zones, are the most vulnerable to global environmental change. Earlier researches indicate that the semi-arid regions are characterized by strong landatmosphere coupling in which soil moisture is the crucial variable in land surface processes. In this paper, we investigate the sensitivity of the sensible/latent heat fluxes to soil moisture during the growing season based on the enhanced observations at Tongyu in the Jilin province of China, a reference site of international Coordinated Energy and Water Cycle Observations Project （CEOP） in the semi-arid regions, by using a sophisticated land surface model （NCAR_CLM3.0）. Comparisons between the observed and simulated sensible/latent heat fluxes indicate that the soil moisture has obvious effects on the sensible/latent heat fluxes in terms of diurnal cycle and seasonal evolution. Better representation of the soil moisture could improve the model performance to a large degree. Therefore, for the purpose of simulating the land-atmosphere interaction and predicting the climate and water resource changes in semi-arid regions, it is necessary to enhance the description of the soil moisture distribution both in the way of observation and its treatment in land surface models.

Application of the Reciprocal Analysis for Sensible and Latent Heat Fluxes with Evapotranspiration at a Humid Region

Evapotranspiration acts an important role in hydrologic cycle and water resources planning. But the estimation issue still remains until nowadays. This research attempts to make clear this problem by the following way. In a humid region, by applying the Bowen ratio concept and optimum procedure on the soil surface, sensible and latent heat fluxes are estimated using net radiation (Rn) and heat flux into the ground (G). The method uses air temperature and humidity at a single height by reciprocally determining the soil surface temperature (Ts) and the relative humidity (rehs). This feature can be remarkably extended to the utilization. The validity of the method is confirmed by comparing of observed and estimated latent (lE) and sensible heat flux (H) using the eddy covariance method. The hourly change of the lE, H, Ts and rehs on the soil surface, yearly change of lE and H and relationship of estimated lE and H versus observed are clarified. Furthermore, monthly evapotranspiration is estimated from the lE. The research was conducted using hourly data of FLUXNET at a site of Japan, three sites of the United States and two sites of Europe in humid regions having over 1000 mm of annual precipitation.

An evaluation of new satellite-derived latent and sensible heat fluxes with moored buoy data, OAFlux and NCEP2 reanalysis products

New satellite-derived latent and sensible heat fluxes are performed by using Wind Sat wind speed, Wind Sat sea surface temperature, the European Centre for Medium-range Weather Forecasting（ECMWF） air humidity, and ECMWF air temperature from 2004 to 2014. The 55 moored buoys are used to validate them by using the 30 min and 25 km collocation window. Furthermore, the objectively analyzed air-sea heat fluxes（OAFlux） products and the National Centers for Environmental Prediction-National Center for Atmospheric Research reanalysis 2（NCEP2） products are also used for global comparisons. The mean biases of sensible and latent heat fluxes between Wind Sat flux results and buoy flux data are –0.39 and –8.09 W/m^2, respectively. In addition, the rootmean-square（RMS） errors of the sensible and latent heat fluxes between them are 5.53 and 24.69 W/m^2,respectively. The RMS errors of sensible and latent heat fluxes are observed to gradually increase with an increasing buoy wind speed. The difference shows different characteristics with an increasing sea surface temperature, air humidity, and air temperature. The zonal average latent fluxes have some high regions which are mainly located in the trade wind zones where strong winds carry dry air in January, and the maximum value centers are found in the eastern waters of Japan and on the US east coast. Overall, the seasonal variability is pronounced in the Indian Ocean, the Pacific Ocean, and the Atlantic Ocean. The three sensible and latent heat fluxes have similar latitudinal dependencies; however, some differences are found in some local regions.

Observation Research of the Turbulent Fluxes of Momentum, Sensible Heat and Latent Heat over the West Pacific Tropical Ocean Area

This paper describes results of the fluxes of momentum , sensible heat and latent heat for the West Pacific Tropical Ocean Area ( 127 ° E - 150 ° E , 5 ° N -3 ° S ). The data were collected by the small tethered balloon sounding system over this ocean area including 6 continuous stations (140 ° E. 0 ° ; 145 ° E, 0 ° ; 150 ° E, 0 ° ; 140° E, 5 ° N; 145 ° E, 5° N and 150 ° E, 5 ° N) from 11 October to 15 December, 1986 . These fluxes were calculated by the semiempirical flux-profile relationships of Monin-Obukhov similarity theory using these observed data. The results show that for this tropical ocean area the drag coefficient CD is equal to (1.53 ± 0.25) × 10 3 and the daily mean latent flux Hl is greater than its daily mean sensible flux HV by a factor of about 9.

Interannual variability of latent and sensible heat fluxes in the South China Sea

The South China Sea (SCS) is significantly influenced by El Nio and the Southern Oscillation (ENSO) through ENSO-driven atmospheric and oceanic changes.We analyzed measurements made from 1960 to 2004 to investigate the interannual variability of the latent and sensible heat fluxes over the SCS.Both the interannual variations of latent and sensible heat fluxes are closely related to ENSO events.The low-pass mean heat flux anomalies vary in a coherent manner with the low-pass mean Southern Oscillation Index (SOI).Time lags between the heat flux anomalies and the SST anomalies were also studied.We found that latent heat flux anomalies have a minimum value around January of the year following El Nio events.During and after the mature phase of El Nio,a change of atmospheric circulation alters the local SCS near-surface humidity and the monsoon winds.During the mature phase of El Nio,the wind speed decreases over the entire sea,and the air-sea specific humidity difference anomalies decreases in the northern SCS and increases in the southern SCS.Thus,a combined effect of wind speed anomalies and air-sea specific humidity difference anomalies results in the latent heat flux anomalies attaining minimum levels around January of the year following an El Nio year.

The Impact of Soil Moisture Availability upon the Partition of Net Radiation into Sensible and Latent Heat Fluxes

The impact of soil moisture availability on the Bowen ratio and on the partition of net radiation flux into sensible, latent and soil heat fluxes was investigated by using one-dimensional primitive equations with a refined soil parameterization scheme. Simulation results presented that as soil moisture availability increases, the Bowen ratio and the partition of net radiation flux into sensible and soil heat fluxes decrease. The partition of net radiation flux into latent heat flux, however, increases. Quantitative relationships between Bowen ratio and the partitions with soil moisture availability were also given in this study.

Variation of fluxes of water vapor, sensible heat and carbon dioxide above winter wheat and maize canopies

Surface energy fluxes were measured using Bowen-Ratio Energy Balance technique (BREB) and eddy correlation system at Luancheng of Hebei Province, on the North China Plain from 1999 to 2001. Average diurnal variation of surface energy fluxes and CO2 flux for maize showed the inverse “U” type. The average peak fluxes did not appear at noon, but after noon. The average peak CO2 flux was about 1.65 mg m-2 s-1. Crop water use efficiency (WUE) increased quickly in the morning, stabilized after 10:00 and decreased quickly after 15:00 with no evident peak value. The ratio of latent heat flux (λE) to net solar radiation (Rn) was always higher than 70% during winter wheat and maize seasons. The seasonal average ratio of sensible heat flux (H) divided byR n stayed at about 15% above the field surface; the seasonal average ratio of conductive heat flux (G) divided by Rn varied between 5% and 13%, and the averageG/R> n from the wheat canopy was evidently higher than that from the maize canopy. The evaporative fraction (EF) is correlated to the Bowen ratio in a reverse function.EF for winter wheat increased quickly during that revival stage, after the stage, it gradually stabilized to 1.0, and fluctuated around 1.0. EF for maize also fluctuated around 1.0 before the later grain filling stage, and decreased after that stage.

Influence of Late Springtime Surface Sensible Heat Flux Anomalies over the Tibetan and Iranian Plateaus on the Location of the South Asian High in Early Summer

Variation in the location of the South Asian High(SAH) in early boreal summer is strongly influenced by elevated surface heating from the Tibetan Plateau(TP) and the Iranian Plateau(IP). Based on observational and ERA-Interim data,diagnostic analyses reveal that the interannual northwestward–southeastward(NW–SE) shift of the SAH in June is more closely correlated with the synergistic effect of concurrent surface thermal anomalies over the TP and IP than with each single surface thermal anomaly over either plateau from the preceding May. Concurrent surface thermal anomalies over these two plateaus in May are characterized by a negative correlation between sensible heat flux over most parts of the TP(TPSH)and IP(IPSH). This anomaly pattern can persist till June and influences the NW–SE shift of the SAH in June through the release of latent heat(LH) over northeastern India. When the IPSH is stronger(weaker) and the TPSH is weaker(stronger)than normal in May, an anomalous cyclone(anticyclone) appears over northern India at 850 hPa, which is accompanied by the ascent(descent) of air and anomalous convergence(divergence) of moisture flux in May and June. Therefore, the LH release over northeastern India is strengthened(weakened) and the vertical gradient of apparent heat source is decreased(increased)in the upper troposphere, which is responsible for the northwestward(southeastward) shift of the SAH in June.

Calibration and validation of SiBcrop Model for simulating LAI and surface heat fluxes of winter wheat in the North China Plain

The accurate representation of surface characteristic is an important process to simulate surface energy and water flux in land-atmosphere boundary layer.Coupling crop growth model in land surface model is an important method to accurately express the surface characteristics and biophysical processes in farmland.However,the previous work mainly focused on crops in single cropping system,less work was done in multiple cropping systems.This article described how to modify the sub-model in the SiBcrop to realize the accuracy simulation of leaf area index(LAI),latent heat flux(LHF)and sensible heat flux(SHF)of winter wheat growing in double cropping system in the North China Plain(NCP).The seeding date of winter wheat was firstly reset according to the actual growing environment in the NCP.The phenophases,LAI and heat fluxes in 2004–2006 at Yucheng Station,Shandong Province,China were used to calibrate the model.The validations of LHF and SHF were based on the measurements at Yucheng Station in 2007–2010 and at Guantao Station,Hebei Province,China in 2009–2010.The results showed the significant accuracy of the calibrated model in simulating these variables,with which the R2,root mean square error(RMSE)and index of agreement(IOA)between simulated and observed variables were obviously improved than the original code.The sensitivities of the above variables to seeding date were also displayed to further explain the simulation error of the SiBcrop Model.Overall,the research results indicated the modified SiBcrop Model can be applied to simulate the growth and flux process of winter wheat growing in double cropping system in the NCP.

THE STUDY ON LATENT AND SENSIBLE HEAT FLUX OVER MIRE IN THE SANJIANG PLAIN

S:Understanding how surface energy fluxes respond to environmental variables and how their components vary on daily and seasonal temporal scales are critical for understanding the ecological process of wetland ecosystem. In view of the fact that studies on surface energy flux over mire in China have been very limited, we have initiated a long-term latent and sensible heat flux (two main components of the surface energy balance) observation over mire in the Sanjiang Plain from June to October in 2004 with the eddy covariance technique. Results showed that the latent and sensible heat flux had large seasonal and diurnal variation during the period of measurement. Generally, latent heat flux between the mire wetland and the atmosphere reached the maximum value in June and then gradually decreased from June to October, whose daily mean fluxes were 9.83,8.00,7.33, 4.82 and 2.04 MJ/(m^2·d), respectively. By comparison, sensible heat flux changed unnoticeably with season change from June to October, which were 1.47,0.88,1.75, 1.61,1.33 MJ/(m^2·d) respectively. The diurnal variation of both latent and sensible heat flux varied noticeably within a day. After the sunrise, the latent and sensible heat flux increased and reached the maximum at noon (11:00-13:00). Then they decreased gradually and reached the minimum value during the nighttime. The patterns of temporal variation in latent and sensible heat flux were significantly controlled by environmental factors. The latent heat flux was linearly dependent on net radiation and increased with increasing vapour pressure deficit until the vapour pressure deficit surpassed 11 hPa. Wind speed effect on latent heat flux was more complicated and, in general, showed a positive correlation between them in daytime. The sensible heat flux was controlled mainly by air temperature difference between the land surface and the overlying air. However, when the temperature difference was larger than 0.3 ℃, it had no effect on the sensible heat flux. The study showed up the temporal variation of latent and sensible heat flux and how the environmental factors affected them.

A study of geographical distributions and temporal variations of air-sea heat fluxes over the Pacific

temporal variations and geographical distributions of sensible and latent heat fluxes over the Pacific were calculated and analyzed by using the Goddard Earth Observing System (GEOS) - four-dimensional Data Assimilation System (DAS). The calculated results showed that the heat flux over the northwestern Pacific varied obviously with seasons, but over the other ocean areas of the Pacific O cean there were no such phenomena. There was always the highest Value region of latent heat fluxes over the Pacific Ocean, but the values of sensible heat fluxes were often very small except over the ocean area north of 20°N and there was not highest value region at all. The latent heat fluxes had different distribu tions with longitude in different latitudes. And the variations of latent heat fluxes with latitude were not the same in different longitude and also it varied with seasons.

Determination of Land Surface Heat Fluxes at Different Temporal Scales over the Tibetan Plateau

Surface energy budget components(such as net radiation flux,sensible heat flux,latent heat flux and soil heat flux)at multiple temporal scales have significant meaning for understanding the energy and water cycle over the Tibetan Plateau(TP).In the framework of ESA-MOST Dragon Programme 4,the surface energy balance system(SEBS)was tested and used to derive surface heat fluxes at different temporal scales over the TP by a combination use of geostationary satellite(FY-2 C)data,polar orbiting satellite(SPOT/VGT,Terra/MODIS)data and ITPCAS forcing data.The validation results show there is a good agreement between derived heat fluxes and in situ measurements from Third Pole Environment Observation and Research Platform(TPEORP),which means the feasibility to derive surface heat fluxes over heterogeneous landscapes by a combination use of geostationary and polar orbiting satellite data in SEBS.The diurnal,seasonal and inter-annual variation characteristics were also clearly identified through analyses of derived turbulent fluxes.

Characteristics of Lake Breezes and Their Impacts on Energy and Carbon Fluxes in Mountainous Areas

In mountainous lake areas, lake–land and mountain–valley breezes interact with each other, leading to an "extended lake breeze". These extended lake breezes can regulate and control energy and carbon cycles at different scales. Based on meteorological and turbulent fluxes data from an eddy covariance observation site at Erhai Lake in the Dali Basin,southwest China, characteristics of daytime and nighttime extended lake breezes and their impacts on energy and carbon dioxide exchange in 2015 are investigated. Lake breezes dominate during the daytime while, due to different prevailing circulations at night, there are two types of nighttime breezes. The mountain breeze from the Cangshan Mountain range leads to N1 type nighttime breeze events. When a cyclonic circulation forms and maintains in the southern part of Erhai Lake at night, its northern branch contributes to the formation of N2 type nighttime breeze events. The prevailing wind directions for daytime, N1, and N2 breeze events are southeast, west, and southeast, respectively. Daytime breeze events are more intense than N1 events and weaker than N2 events. During daytime breeze events, the lake breeze decreases the sensible heat flux(Hs) and carbon dioxide flux(F_(CO_2)) and increases the latent heat flux(LE). During N1 breeze events, the mountain breeze decreases Hs and LE and increases F_(CO_2). For N2 breeze events, the southeast wind from the lake surface increases Hs and LE and decreases suppress carbon dioxide exchange.

An improved algorithm of simulation on air-sea turbulent heat fluxes in China seas

With a global GSSTF2 and NCEP/NCAR reanalysis database and observation data at the Yong Xing station of Xisha Island in the South China Sea, we simulated the turbulent sensible and latent heat flux at sea surface in Chinese and neighboring seas (hereafter termed as China seas) using a common bulk method with some improved parameters. Comparing the simulated results with the observed and reanalyzed data, the improvement yielded higher accuracy, a smaller mean square deviation within 10 W/m2, and a smaller average relative error at about 25%. In addition, spatial resolution was improved to 0.1°×0.1°. The simulation is able to replay the main features of regional and seasonal variation in turbulent heat fluxes, and also the general pattern of heat flux changes during the summer monsoon outbreak in the South China Sea.

Model calculation of air-sea heat fluxes over ocean area near China with GEOS DAS system

The sensible and latent heat fluxes over the ocean area near China were calculated and analyzed by usingthe Goddard Earth Observing System (GEOS) - four-dimensional Data Assimilation System (DAS). The calculated results showed that the sensible heat flux had its large value in winter and autumn , small value in spring and summer overthe ocean area near China. In winter, the sensible heat flux increased distinctly with latitude, and its isolines were verycrowded. Over the ocean area east of Taiwan Province and south of Japan, the direction of isoline was from southwestto northeast. In the South China Sea the sensible heat flux was lower than that of surrounding ocean areas,and its isoline was distributed into a type of an inverted trough. In autumn and winter, the maximum center of latent heat flux appeared over the ocean area northeast of Taiwan Province and south and southeast of Japan, meanwhile, the isoline wasin the direction of southwest to northeast. In spring and summer, the latent heat flux had minimum value in the Huanghai Sea. At the same time, the maximum value center of latent heat flux appeared over the ocean area south of Japan inspring.

The seasonal variability of an air-sea heat flux in the northern South China Sea

The seasonal variabilities of a latent-heat flux （LHF）, a sensible-heat flux （SHF） and net surface heat flux are examined in the northern South China Sea （NSCS）, including their spatial characteristics, using the in situ data collected by ship from 2006 to 2007. The spatial distribution of LHF in the NSCS is mostly controlled by wind in summer and autumn owing to the lower vertical gradient of air humidity, but is influenced by both wind and near-surface air humidity vertical gradient in spring and winter. The largest area-averaged LHF is in autumn, with the value of 197.25 W/m 2 , followed by that in winter; the third and the forth are in summer and spring, respectively. The net heat flux is positive in spring and summer, so the NSCS absorbs heat; and the solar shortwave radiation plays the most important role in the surface heat budget. In autumn and winter, the net heat flux is negative in most of the observation region, so the NSCS loses heat; and the LHF plays the most important role in the surface heat budget. The net heating is mainly a result of the offsetting between heating due to the shortwave radiation and cooling due to the LHF and the upward （outgoing） long wave radiation, since the role of SHF is negligible. The ratio of the magnitudes of the three terms （shortwave radiation to LHF to long-wave radiation） averaged over the entire year is roughly 3：2：1, and the role of SHF is the smallest.

CHARACTERISTICS OF HEAT FLUX OVER THE TROPICAL WESTERN PACIFIC DURING THE IOP OF TOGA-COARE

Based on the surface meteorological and radiosonde data during the IOP of TOGA-COARE (Tropical Ocean Global Atmospheric-Coupled Ocean Atmospheric Response Experiment) at the observation site (2°15′S, 158°E)of "R/V Shiyan 3", characteristics of the heat flux, especially that pertaining two WWBs (westerly wind bursts)over the tropical western Pacific for the IOP, are exhaustively analyzed. Meanwhile, the relationships among large-scale circulation and mid-and-high latitude circulation are discussed. The results show that the latent and sensible heat fluxes from sea surface to air over the tropical western Pacific are very strong in both the WWBs,and that their causes of formation have important relations with cross-equatorial flow from the winter hemisphere,and the heat exchange over sea surface varies with different weather condition.

Near-Surface Wind-Speed Stilling in Alaska during 1984-2016 and Its Impact on the Sustainability of Wind Power

Based on wind-speed records of Alaska’s 19 first-order weather stations, we analyzed the near-surface wind-speed stilling for January 1, 1984 to December 31, 2016. With exception of Big Delta that indicates an increase of 0.0157 m·s–1·a–1, on average, all other first-order weather stations show declining trends in the near-surface wind speeds. In most cases, the average trends are less then?–0.0300?m·s–1·a–1. The strongest average trend of?–0.0500?m·s–1·a–1 occurred at Homer, followed by?–0.0492?m·s–1·a–1 at Bettles, and?–0.0453?m·s–1·a–1 at Yakutat, while the declining trend at Barrow is marginal. The impact of the near-surface wind-speed stilling on the wind-power potential expressed by the wind-power density was predicted and compared with the wind-power classification of the National Renewable Energy Laboratory and the Alaska Energy Authority. This wind-power potential is, however, of subordinate importance because wind turbines only extract a fraction of the kinetic energy from the wind field characterized by the power efficiency. Since wind turbine technology has notably improved during the past 35 years, we hypothetically used seven currently available wind turbines of different rated power and three different shear exponents to assess the wind-power sustainability under changing wind regimes. The shear exponents 1/10, 1/7, and 1/5 served to examine the range of wind power for various conditions of thermal stratification. Based on our analysis for January 1, 1984 to December 31, 2016, Cold Bay, St. Paul Island, Kotzebue, and Bethel would be very good candidates for wind farms. To quantify the impact of a changing wind regime on wind-power sustainability, we predicted wind power for the periods January 1, 1984 to December 31, 1994 and January 1, 2006 to December 31, 2016 as well. Besides Big Delta that suggests an increase in wind power of up to 12% for 1/7, predicted wind power decreased at all sites with the highest decline at Annette (≈38%), Kodiak (≈30%), King Salmon (≈26%), and Kotzebue (≈24%), where the effect of the shear exponents was marginal. Bethel (up to 20%) and Cold Bay (up to 14%) also show remarkable decreases in predicted wind power.

A Case Study of Ocean-Atmosphere Interactions during the Passage of an Extra-Tropical Cyclone in the Vicinity of Cape Hatteras, North Carolina

The authors document the interaction of the atmosphere and ocean during the formation and passage of an Extra-Tropical Cyclone, which is a Nor-Easter, winter storm that formed in the southern apex of the Middle Atlantic Bight near Cape Hatteras North Carolina, between February 15 and 18, 1996. While Nor-Easters per se, which have formed along the Atlantic Eastern Seaboard of the United States have been studied for decades, the actual atmospheric-oceanic mechanics and thermodynamics in the formation of a Nor-Easter has never been documented. We report on having done so with in-situ observations and data-based calculations and a numerical model. The in-situ observations were made via a Control Volume consisting of an array of Eulerian Oceanic-Atmospheric Moorings with current meters, temperature and salinity sensors and meteorological towers. We find that Gulf Stream waters were located surrounding the mooring array, and that with the invasion of cold dry atmospheric air, there was a rapid loss of heat from the ocean to the atmosphere via latent and sensible surface heat flux during the cyclogenesis onset of the storm. A unique feature of this storm was that neither satellite nor buoy data showed significant sea surface cooling in the control volume. The findings indicate that storm winds drove warm saline waters from the Gulf Stream across the continental shelf into the control volume, accounting for a 51 cm rise in water level along the coast. This lateral heat advection provided heat to the control volume of 3.4e+18 Joules. On average, the heat loss at the surface of the control volume, via sensible and latent heat fluxes and radiation, was 0.7e+18 Joules, corresponding to a surface heat flux of -600 Watts per Meter2 (W/m2). However, the heat lost by the control volume as latent and sensible heat fluxes was less than the heat it received via lateral heat advection, resulting in the lack of an often-observed sea surface cooling during other winter storms. The serendipitous and detailed observations and calculations reveal a climatological flywheel in this region, documenting the role of ETCs in the global heat balance.

利用Landsat遥感影像进行福州市地表热通量估算的研究试验

利用福州市1989年和2001年Landsat TM/ETM+遥感影像数据估算地表温度、地表反照率和植被覆盖度等地表参数,再结合气象站观测资料,估算与城市热岛密切相关的气候因子即显热通量和潜热通量。然后根据植被覆盖度对由人工建筑物和水泥道路等构成的不透水面覆盖区的潜热通量进行修正,改进了不透水面潜热通量的计算,并且探讨了地表热通量随土地覆盖变化的时空分布特征。最后对地表热通量精度进行分析和检验,论证了本研究的地表热通量估算结果是合理的。