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Vinukollu R.K.,Swiss Re | Sahoo A.,Princeton University | Sheffield J.,Princeton University | Wood E.F.,Princeton University
IAHS-AISH Publication | Year: 2012

Deriving overland evapotranspiration (ET) estimates is an important part of the larger effort to develop long-term Earth System Data Records (ESDRs) for the major components (storages and fluxes) of the terrestrial water cycle. In the current study, global estimates of sensible heat and evaporative fluxes are developed for 1984-2006 using three process-based models forced by two remote sensing based data sets. The models are surface energy balance system (SEBS), a modified Penman-Monteith approach, and a Priestley-Taylor approach. The models are driven by radiation inputs from the ISCCP and SRB data sets, with the meteorological forcing data from ISCCP, and vegetation characteristics from AVHRR. Estimates are made using the three models. Comparisons among the data sets show large differences in magnitude and long-term variability, due mainly to uncertainties in the forcing radiation. Comparisons with independent data sets from inferred evaporation estimates [(P-Q)climatology], off-line land surface model (VIC) data, previously developed remote sensing products and estimates derived from tower data, reveals consistency at large scales, but large differences in some regions, most notably in the northern hemisphere. Copyright © 2012 IAHS Press.

Gontis V.,Vilnius University | Kononovicius A.,Vilnius University | Reimann S.,Swiss Re
Advances in Complex Systems | Year: 2012

We investigate behavior of the continuous stochastic signals above some threshold, bursts, when the exponent of multiplicativity is higher than one. Earlier we have proposed a general nonlinear stochastic model applicable for the modeling of absolute return and trading activity in financial markets which can be transformed into Bessel process with known first hitting (first passage) time statistics. Using these results we derive PDF of burst duration for the proposed model. We confirm derived analytical expressions by numerical evaluation and discuss bursty behavior of return in financial markets in the framework of modeling by nonlinear SDE. © 2012 World Scientific Publishing Company.

Badgley G.,Carnegie Institution for Science | Fisher J.B.,Jet Propulsion Laboratory | Jimenez C.,French National Center for Scientific Research | Vinukollu R.,Swiss Re
Journal of Hydrometeorology | Year: 2015

Evapotranspiration ET is a critical water, energy, and climate variable, and recent work has been published comparing different global products. These comparisons have been difficult to interpret, however, because in most studies the evapotranspiration products were derived frommodels forced by different input data. Some studies have analyzed the uncertainty in regional evapotranspiration estimates from choice of forcings. Still others have analyzed how multiple models vary with choice of net radiation forcing data. However, no analysis has been conducted to determine the uncertainty in global evapotranspiration estimates attributable to each class of input forcing datasets. Here, one of these models [Priestly-Taylor JPL (PT-JPL)] is run with 19 different combinations of forcing data. These data include three net radiation products (SRB, CERES, and ISCCP), three meteorological datasets [CRU, Atmospheric Infrared Sounder (AIRS)Aqua, andMERRA], and three vegetation index products [MODIS; Global Inventory Modeling and Mapping Studies (GIMMS); and Fourier-Adjusted, Sensor and Solar Zenith Angle Corrected, Interpolated, Reconstructed (FASIR)]. The choice in forcing data produces an average range in global monthly evapotranspiration of 10.6Wm-2 (~20% of global mean evapotranspiration), with net radiation driving themajority of the difference. Annual average terrestrial ET varied by an average of 8Wm-2, depending on choice of forcings. The analysis shows that the greatest disagreement between input forcings arises from choice of net radiation dataset. In particular, ISCCP data, which are frequently used in global studies, differed widely from the other radiation products examined and resulted in dramatically different estimates of global terrestrial ET. © 2015 American Meteorological Society.

Buhler J.,ETH Zurich | Oehy C.,Swiss Re | Oehy C.,Ecole Polytechnique Federale de Lausanne | Schleiss A.J.,Ecole Polytechnique Federale de Lausanne
Journal of Hydraulic Engineering | Year: 2013

Hydraulic jumps at the tail end of spillways are usually induced by baffle blocks or other obstacles. Such jumps can also be induced by jets that oppose the main flow. Another application is to back up turbidity currents in reservoirs by means of opposing jets. This measure can be adopted when transfer tunnels feed water into the reservoir at a higher elevation near the dam. Stopping the turbidity current increases the local sedimentation rate. To reconcile the shallow water equations for turbidity currents with those for open channel flows, massbased scales for the depth and velocity of both types of flows are outlined. The continuity and momentum equation for flows opposed by jets are then stated in terms of these scales and expressed by a single curve for both gravity currents and free surface flows. The corresponding results for free surface flows agree well with those of experiments carried out for this study. An application to turbidity currents is provided as well. © 2013 American Society of Civil Engineers.

Ferguson C.R.,University of Tokyo | Wood E.F.,Princeton University | Vinukollu R.K.,Swiss Re
Journal of Hydrometeorology | Year: 2012

Land-atmosphere coupling strength or the degree to which land surface anomalies influence boundary layer development-and in extreme cases, rainfall-is arguably the single most fundamental criterion for evaluating hydrologicalmodel performance. TheGlobal Land-Atmosphere Coupling Experiment (GLACE) showed that strength of coupling and its representation can affect a model's ability to simulate climate predictability at the seasonal time scale. And yet, the lack of sufficient observations of coupling at appropriate temporal and spatial scales has made achieving "true" coupling in models an elusive goal. This study uses Advanced Microwave Scanning Radiometer for Earth Observing System (AMSR-E) soil moisture (SM), multisensor remote sensing (RS) evaporative fraction (EF), andAtmospheric Infrared Sounder (AIRS) lifting condensation level (LCL) to evaluate the realism of coupling in the Global Land Data Assimilation System (GLDAS) suite of land surface models (LSMs), Princeton Global Forcing Variable Infiltration Capacity model (PGF-VIC), seven global reanalyses, and the North American Regional Reanalysis (NARR) over a 5-yr period (2003-07). First, RS and modeled estimates of SM, EF, and LCL are intercompared. Then, emphasis is placed on quantifying RS and modeled differences in convective-season daily correlations between SM-LCL, SM-EF, and EF-LCL for global, regional, and conditional samples. RS is found to yield a substantially weaker state of coupling than model products. However, the rank order of basins by coupling strength calculated from RS and models do roughly agree. Using a mixture of satellite and modeled variables, a map of hybrid coupling strength was produced, which supports the findings of GLACE that transitional zones tend to have the strongest coupling. © 2012 American Meteorological Society.

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