A22B-01
Progress on the observational study of land surface processes over the Tibetan Plateau Area
As the most prominent and complicated terrain on the global, the Tibetan Plateau, with an elevation of more than 4000 m on average above mean sea leave makes up approximately one fourth of the land area of China. Long-term operation and research on the Tibetan Plateau have shown that the giant prominence expert thermal effects on the atmosphere, thus greatly influencing atmospheric circulations over China, Asia and even the global. Due to its topographic character, the plateau surface absorbs a large amount of solar radiation energy and undergoes dramatic seasonal changes of surface heat and water fluxes. The lack of quantitative understanding of interactions between the land surface and atmosphere makes it difficult to understand the complete energy and water cycles over the Tibetan Plateau and their effects on the Asian Monsoon system by numerical models. Therefore, the study on energy exchange and water cycle are regarded as the main task in the GEWEX (Global Energy and Water cycle Experiment) Asian Monsoon Experiment on the Tibetan Plateau (GAME/Tibet, 1996-2000) and CEOP (Coordinated Enhanced Observing Period) Asia-Australia Monsoon Project (CAMP) on the Tibetan Plateau (CAMP/Tibet, 2001-2005). The intensive observation and long-term observation of the GAME/Tibet and the CAMP/Tibet have been done successfully in the past 8 years. A large amount of data has been collected, which is the best data set so far for the study of land surface heat flux and water cycle over the Tibetan Plateau. Firstly, the field experiments and some results on the local land surface fluxes partitioning (imbalance ±, diurnal variation, inter-monthly variation, inter-yearly variation and vertical variation etc) will be presented. In order to upscale 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 land surface and atmospheric processes on the Tibetan Plateau. The establishing and monitoring plan of long-term scale (5-10 years) of the MORP, three new comprehensive observation and study stations (Mt.Qomolangma, Nam Cuo and Linzhi) and some results of data analysis on the Mt.Qomolangma station and Nam Cuo station will also be introduced here.
A22B-02
Determination of the Regional Land use and Energy Fluxes Over the Upper Xilin River Watershed by Landsat Data of two Contrasting Years
The Inner Mongolia grassland in China is representative for semi-arid grassland in temperate zones. It is one of the most important land covers over the globe and covers large areas of China. Studying of the land surface processes in this region will improve the understanding of the regional climate formation and its feedback with global climate change. Satellite remote sensing provides an excellent opportunity to study the land- atmosphere interaction on a regional scale. In this paper, the regional distributions of the land surface energy fluxes (net radiation, soil heat flux, sensible heat flux and latent heat flux) over the upper Xilin River watershed in Inner Mongolia, China were derived using established methods with two Landsat scenes in 2000 and 2005, respectively. The derived results including land surface variables were validated with field measurements. Due to different time of the year (July and August) and different precipitation before the satellite overpass, the two scenes show expected differences. The cases studies to map the regional land surface energy fluxes in the upper Xilin River watershed shows promising results and forms a sound foundation to study the land surface process in semi-arid grassland by remote sensing and also gives valuable guidance for further investigation for the whole watershed.
A22B-03
Overall Evaluation of Surface Flux Parameterization Schemes for Bare Soil Surfaces
Bare soil is a major landscape in arid and semi-arid regions. Heat flux parameterization schemes for bare soil surfaces play a crucial role in modeling land-atmosphere interactions in this region and they are also a basis for developing sparse-canopy heat transfer schemes. This study presented evaluation of six flux schemes in literature using a number of data, which were collected at eight flux stations in arid and semi-arid region of China. These stations represent a variety of surface conditions: they were located at the Tibetan Plateau, Gobi, desert, cropland, and degraded grassland, their altitudes range from near-sea surface up to several kilometers, surface roughness from less than 1 mm up to 1 cm, and sensible heat fluxes from -50 W/m2 up to more than 400 W m/m2. This analysis shows that two schemes among the six can reliably estimate heat fluxes and momentum fluxes at most of the bare soil surfaces, while other four schemes systematically and significantly over-estimate or under-estimate fluxes. The effect of flux parameterization schemes on modeled surface temperature and energy partition was also discussed.
A22B-04
Revisiting Two-stream Radiation Transfer Schemes Implemented in Climate Models
The amount of radiation absorbed in the photosynthetically active spectral region, scattered in the visible and near-infrared domains as well as the Leaf Area Index (LAI), are operationally available from Space Agencies. Climate models may benefit from these products provided their one dimensional radiation transfer schemes effectively represent, when appropriate, the three dimensional effects implied by the internal spatial variability of vegetation canopies, e.g., the leaf area density, at all scales and resolutions involved (typically from 1 to 100 kilometers). Failing to do so leads to inherent inconsistencies between the domain-averaged reflected and absorbed fluxes, and the implied Leaf Area Index. We propose a comprehensive approach which introduces a parameterization of the internal variability of the LAI in the 1-D representation of the radiation scheme, called a domain-averaged structure factor, and provides a description of the radiant fluxes fully consistent with the LAI specified by remote sensing. We take this opportunity to revisit and update the two-stream formulations implemented in climate models to accurately estimate the fractions of radiation absorbed separately by the vegetation canopy and the underlying surface.
http://fapar.jrc.it/WWW/Data/Pages/FAPAR_Sof tware/
A22B-05
An Investigation of Vegetative and Atmospheric Conductance Forcing on the Bouchet - Morton Complementary Relationship Hypothesis using Sap Flux Observations at Harvard Forest
Indirect methods of quantifying evapotranspiration ({\it ET$_{a}$}) are sought since regional estimations of {\it ET$_{a}$} require prohibitive instrumentation or highly parameterized and data intensive land surface models ({\it e.g.}, involving temporally and spatially-varying soil moisture, soil hydraulic properties, and vegetation properties). Complementary relationship (CR) models, based on Bouchet`s heuristic hypothesis, are one such method of estimating {\it ET$_{a}$} from routinely-measured meteorological variables. The treatment of vegetation in existing CR applications varies from neglecting physiological controls on transpiration to indirectly accounting for such regulatory mechanisms through recalibration of Penman`s empirical wind function. Moreover, the leading theoretical models ({\it e.g.}, Morton, Granger, Szilagyi) of the coupled land surface - atmosphere mechanisms responsible for CR focus primarily on vertical humidity (vapor pressure) profiles while assuming that vegetative and/or atmospheric diffusivities play an insignificant role in regulating CR. As such, we conducted CR evaluations at both temperate grassland (FIFE) and mixed-deciduous forest (Harvard Forest) ecosystems to investigate how vegetative and atmospheric diffusivities regulate CR-type behavior. Our field campaign at Harvard Forest involved an intensive irrigation program to investigate the underlying CR assumption that {\it ET$_{p}$} is synonymous with unlimited water availability. Root-zone soil moisture of a red maple ({\it Acer rubrum} L.) sample set was elevated using a pulse-irrigation system. Whole-tree transpiration of the 'potential' (water-unstressed) and a reference (water-stressed) set of maples was monitored at high frequency using heat-dissipation Granier-type sap flux sensors. Preliminary results suggest the following: (1) the absence of an unstressed canopy conductance in the Penman equation results in violation of fundamental CR assumptions for both FIFE and Harvard Forest; (2) unlimited root-zone water availability does not reduce the leaf-level stomatal resistance enough to yield a Penman-type {\it ET$_{p}$} signal, suggesting that the complementarity of the {\it ET$_{p}$} signal is also a function of other environmental stresses, {\it e.g.}, vapor pressure deficit; (3) eddy covariance measurements demonstrate that wind speed, and thus atmospheric conductance, increases with a reduction in regional moisture availability; and (4) estimations of the scalar roughness length for water vapor (z$_{ov}$) may counterbalance the lack of a canopy conductance in the Penman {\it ET$_{p}$} flux. In summary, our results yield valuable insight into how vertical atmospheric and vegetative diffusivities should not be neglected in theoretical advancements of Bouchet's heuristic CR hypothesis.
http://people.bu.edu/geocory/
A22B-06
Incorporating Stable Water Isotopes in the Community Land Model
Stable water isotopes are added to the Community Land Model (CLM) as a diagnostic tool for an in-depth understanding of the hydrologic and thermal processes. This paper will describe how the isotope mass balance equations are formulated for the canopy surface water stores and the surface soil layers. Fractionations of isotopes are involved in many hydrologic processes including canopy evaporation, dew formation, and soil evaporation and condensation. The performance of the isotope submodel will be assessed by using a meteorological forcing dataset representing a tropical rainforest provided by the Project for Intercomparison of Land-surface Parameterization Schemes with isotopes (iPILPS).
http://www.geo.utexas.edu/climate
A22B-07
The Warming of the Continents
The recent global warming of the surface air temperature (SAT) is well documented in the instrumental records. The impact of this temperature change is not restricted to the Earth's surface. Any global scale change in SAT is accompanied by the change of the thermal state of all major climate system components including the lithosphere. In this study I first analyze the heat content change of the continental landmasses from Year 1851 to Year 2005. I then continue the analysis to 2100 under three different scenarios. The first scenario assumes that the global warming trend were to continue at the same rate as we have seen over the last 25 years. The second scenario assumes that the surface temperature in the near future is to stabilize at the five-year mean temperature between Year 2001 and Year 2005. In the third scenario, I examine the ground surface temperature condition required for the continental heat budget to remain unchanged over the rest of the 21st century. This analysis shows that the recent global climate change has led to an intensified heating in the continental landmasses. The observed global SAT warming has posted a transient perturbation to the subsurface temperature down to a depth of about 200m, and is responsible for a net energy gain of over 11 Zetta Joules by the uppermost continental lithosphere. The expected lithosphere warming is consistent with world-wide borehole temperature records. If the observed global warming trend over the past 25 years were to continue, an additional 50 ZJ of heat will be trapped underground by the end of the 21st century. Even if the global surface temperature would stabilize at the current state, the continental landmasses will continue to pick up extra energy from the atmosphere. In order to prevent the continental lithosphere from further warming, a progressive cooling of about 0.7 K at the global ground surface between now and the end of this century is required.