scholarly journals Evaluating Observation Influence on Regional Water Budgets in Reanalyses

2015 ◽  
Vol 28 (9) ◽  
pp. 3631-3649 ◽  
Author(s):  
Michael G. Bosilovich ◽  
Jiun-Dar Chern ◽  
David Mocko ◽  
Franklin R. Robertson ◽  
Arlindo M. da Silva
Keyword(s):  
United States ◽  
Moisture Flux ◽  
Physical Processes ◽  
Flux Divergence ◽  
Water Budgets ◽  
Central United States ◽  
Anomalous Feature ◽  
Closed Water ◽  
Regional Water ◽  
Moisture Flux Divergence

Abstract The assimilation of observations in reanalyses incurs the potential for the physical terms of budgets to be balanced by a term relating the fit of the observations relative to a forecast first guess analysis. This may indicate a limitation in the physical processes of the background model or perhaps assimilating data from an inconsistent observing system. In the MERRA reanalysis, an area of long-term moisture flux divergence over land has been identified over the central United States. Here, the water vapor budget is evaluated in this region, taking advantage of two unique features of the MERRA diagnostic output: 1) a closed water budget that includes the analysis increment and 2) a gridded diagnostic output dataset of the assimilated observations and their innovations (e.g., forecast departures). In the central United States, an anomaly occurs where the analysis adds water to the region, while precipitation decreases and moisture flux divergence increases. This is related more to a change in the observing system than to a deficiency in the model physical processes. MERRA’s Gridded Innovations and Observations (GIO) data narrow the observations that influence this feature to the ATOVS and Aqua satellites during the 0600 and 1800 UTC analysis cycles, when radiosonde information is not prevalent. Observing system experiments further narrow the instruments that affect the anomalous feature to AMSU-A (mainly window channels) and Atmospheric Infrared Sounder (AIRS). This effort also shows the complexities of the observing system and the reactions of the regional water budgets in reanalyses to the assimilated observations.

scholarly journals The Atmospheric Water Balance over the Semiarid Murray–Darling River Basin

2008 ◽  
Vol 9 (3) ◽  
pp. 521-534 ◽  
Author(s):  
Clara Draper ◽  
Graham Mills
Keyword(s):  
Surface Water ◽  
Water Balance ◽  
River Basin ◽  
Moisture Flux ◽  
Limited Area ◽  
Consecutive Series ◽  
Atmospheric Water ◽  
Flux Divergence ◽  
Murray Darling Basin ◽  
Moisture Flux Divergence

Abstract The atmospheric water balance over the semiarid Murray–Darling River basin in southeast Australia is analyzed based on a consecutive series of 3- to 24-h NWP forecasts from the Australian Bureau of Meteorology’s Limited Area Prediction System (LAPS). Investigation of the LAPS atmospheric water balance, including comparison of the forecast precipitation to analyzed rain gauge observations, indicates that the LAPS forecasts capture the general qualitative features of the water balance. The key features of the atmospheric water balance over the Murray–Darling Basin are small atmospheric moisture flux divergence (at daily to annual time scales) and extended periods during which the atmospheric water balance terms are largely inactive, with the exception of evaporation, which is consistent and very large in summer. These features present unique challenges for NWP modeling. For example, the small moisture fluxes in the basin can easily be obscured by the systematic errors inherent in all NWP models. For the LAPS model forecasts, there is an unrealistically large evaporation excess over precipitation (associated with a positive bias in evaporation) and unexpected behavior in the moisture flux divergence. Two global reanalysis products (the NCEP Reanalysis I and the 40-yr ECMWF Re-Analysis) also both describe (physically unrealistic) long-term negative surface water budgets over the Murray–Darling Basin, suggesting that the surface water budget cannot be sensibly diagnosed based on output from current NWP models. Despite this shortcoming, numerical models are in general the most appropriate tool for examining the atmospheric water balance over the Murray–Darling Basin, as the atmospheric sounding network in Australia has extremely low coverage.

Ten Years of Measurements of Tropical Upper-Tropospheric Water Vapor by MOZAIC. Part II: Assessing the ECMWF Humidity Analysis

2008 ◽  
Vol 21 (7) ◽  
pp. 1449-1466 ◽  
Author(s):  
Zhengzhao Luo ◽  
Dieter Kley ◽  
Richard H. Johnson ◽  
Herman Smit
Keyword(s):  
Water Vapor ◽  
Annual Cycle ◽  
Deep Convection ◽  
Moisture Flux ◽  
Forecast Model ◽  
Enso Event ◽  
Flux Divergence ◽  
Asian Monsoon Region ◽  
Dry Bias ◽  
Moisture Flux Divergence

Abstract In a recent publication (Part I), the authors introduced a data source—Measurement of Ozone and Water Vapor by Airbus In-Service Aircraft (MOZAIC)—for monitoring and studying upper-tropospheric water vapor (UTWV) and analyzed 10 yr (1994–2004) of MOZAIC measurements of tropical UTWV in its climatology, variability, transport, and relation to deep convection. In this study (Part II), MOZAIC is used to assess the ECMWF humidity analysis over the tropics, taking advantage of the unique nature of the MOZAIC data, namely, the long data record, near-global coverage, and high accuracy. In parallel to Part I, the ECMWF UTWV analysis is assessed against MOZAIC in the following five aspects: 1) annual cycle, 2) vertical structure, 3) probability density functions (PDFs), 4) moisture flux divergence, and 5) interannual variability. The annual cycle of the ECMWF UTWV shows a similar pattern as MOZAIC but has an overall dry bias of about 10%–30% relative humidity with respect to ice (RHi). The dry biases are larger in the deep tropics than the subtropics and larger over the Asian monsoon region than the tropical Atlantic region. The increase in RH with height (from about 300 to 200 hPa) as observed by MOZAIC is largely missing in the ECMWF analysis, which has a roughly constant RH profile. The bimodal distribution of tropical UTWV is well established in MOZAIC, but for ECMWF, the moist mode is abruptly cut off at 100% RHi due to the lack of ice supersaturation (ISS) in the forecast model. Lack of ISS capability is, however, not the only cause for the dry bias in the ECMWF; it also has more occurrences of lower humidity compared to MOZAIC. There is also evidence that ECMWF underestimates the range of upper-tropospheric humidity (UTH) variation. A comparison of moisture flux divergence is conducted to assess the ability of ECMWF to capture the divergent transport of water vapor. It is shown that the ECMWF can represent the distribution of this quantity fairly well, although the dry bias leads to some underestimate of the magnitude. Finally, the authors show a comparison of the ECMWF and MOZAIC depictions of the interannual variation of UTWV during the 1997/98 ENSO event as an illustration that UTWV variations are more difficult to capture than those of the UT temperature.

scholarly journals A Water Balance–Based, Spatiotemporal Evaluation of Terrestrial Evapotranspiration Products across the Contiguous United States

2018 ◽  
Vol 19 (5) ◽  
pp. 891-905 ◽  
Author(s):  
Elizabeth Carter ◽  
Christopher Hain ◽  
Martha Anderson ◽  
Scott Steinschneider
Keyword(s):  
United States ◽  
Energy Balance ◽  
Interannual Variability ◽  
Water Budget ◽  
Water Budgets ◽  
Central United States ◽  
Precipitation Estimates ◽  
Terrestrial Water ◽  
Gauged Basins

Abstract Accurate gridded estimates of evapotranspiration (ET) are essential to the analysis of terrestrial water budgets. In this study, ET estimates from three gridded energy balance–based products (ETEB) with independent model formations and data forcings are evaluated for their ability to capture long-term climatology and interannual variability in ET derived from a terrestrial water budget (ETWB) for 671 gauged basins across the contiguous United States. All three ETEB products have low spatial bias and accurately capture interannual variability of ETWB in the central United States, where ETEB and ancillary estimates of change in total surface water storage (ΔTWS) from the GRACE satellite project appear to close terrestrial water budgets. In humid regions, ETEB products exhibit higher long-term bias, and the covariability of ETEB and ETWB decreases significantly. Several factors related to either failure of ETWB, such as errors in ΔTWS and precipitation, or failure of ETEB, such as treatment of snowfall and horizontal heat advection, explain some of these discrepancies. These results mirror and build on conclusions from other studies: on interannual time scales, ΔTWS and error in precipitation estimates are nonnegligible uncertainties in ET estimates based on a terrestrial water budget, and this confounds their comparison to energy balance ET models. However, there is also evidence that in at least some regions, climate and landscape features may also influence the accuracy and long-term bias of ET estimates from energy balance models, and these potential errors should be considered when using these gridded products in hydrologic applications.

scholarly journals Boundary condition and oceanic impacts on the atmospheric water balance in limited area climate model ensembles

2021 ◽  
Vol 11 (1) ◽  
Author(s):  
Klaus Goergen ◽  
Stefan Kollet
Keyword(s):  
Boundary Conditions ◽  
Climate Models ◽  
Climate Model ◽  
Regional Climate ◽  
Moisture Flux ◽  
Limited Area ◽  
Atmospheric Moisture ◽  
Atmospheric Water ◽  
Flux Divergence ◽  
Water Budgets

AbstractRegional climate models (RCMs) are indispensable in climate research, albeit often characterized by biased terrestrial precipitation and water budgets. This study identifies excess oceanic evaporation, in conjunction with the RCMs’ boundary conditions, as drivers contributing to these biases in RCMs with forced sea surface temperatures in a CORDEX RCM ensemble over Europe. The RCMs are relaxed to the prescribed lateral boundary conditions originating from a global model, effectively matching the driving model's overall atmospheric moisture flux divergence. As a consequence, excess oceanic evaporation results in positive precipitation biases over land due to forced internal recycling of moisture to maintain the overall flux divergence prescribed by the boundary conditions. This systematic behaviour is shown through an analysis of long-term atmospheric water budgets and atmospheric moisture exchange between oceanic and continental areas in a multi-model ensemble.

Hawaiian Regional Climate Variability during Two Types of El Niño

2020 ◽  
Vol 33 (22) ◽  
pp. 9929-9943
Author(s):  
Bo-Yi Lu ◽  
Pao-Shin Chu ◽  
Sung-Hun Kim ◽  
Christina Karamperidou
Keyword(s):  
El Niño ◽  
North Pacific ◽  
El Nino ◽  
Moisture Flux ◽  
Jet Stream ◽  
Flux Divergence ◽  
The North ◽  
The Impact ◽  
The North Pacific ◽  
Moisture Flux Divergence

AbstractThe large-scale atmospheric circulation of the North Pacific associated with two types of El Niño—the eastern Pacific (EP) and central Pacific (CP)—is studied in relation to Hawaiian winter (December–February) rainfall and temperature. The eastern and central equatorial Pacific undergo active convective heating during EP El Niño winters. The local Hadley circulation is enhanced and an upper-level westerly jet stream of the North Pacific is elongated eastward. Due to the impact of both phenomena, stronger anomalous descending motion, moisture flux divergence anomalies near Hawaii, and reduction of easterly trade winds, which are characteristic of EP winters, are unfavorable for winter rainfall in Hawaii. As a result of this robust signal, dry conditions prevail in Hawaii and the standard deviation of rainfall during EP winters is smaller than the climatology. For CP winters, the maximum equatorial ocean warming is weaker and shifted westward to near the date line. The subtropical jet stream retreats westward relative to EP winters and the anomalously sinking motion near Hawaii is variable and generally weaker. Although the anomalous moisture flux divergence still exists over the subtropical North Pacific, its magnitude is weaker relative to EP winters. Without strong external forcing, rainfall in the Hawaiian Islands during CP winters is close to the long-term mean. The spread of rainfall from one CP event to another is also larger. The near-surface minimum temperature from three stations in Hawaii reveals cooling during EP winters and slight warming during CP winters.

scholarly journals Biases of the observed atmospheric water budgets over the central United States

1999 ◽  
Vol 104 (D16) ◽  
pp. 19349-19360 ◽  
Author(s):  
Evgeney S. Yarosh ◽  
Chester F. Ropelewski ◽  
Ernesto H. Berbery
Keyword(s):  
United States ◽  
Atmospheric Water ◽  
Water Budgets ◽  
Central United States

scholarly journals Uncertainties in Estimating Moisture Fluxes over the Intra-Americas Sea

2005 ◽  
Vol 6 (5) ◽  
pp. 696-709 ◽  
Author(s):  
Alberto M. Mestas-Nuñez ◽  
Chidong Zhang ◽  
David B. Enfield
Keyword(s):  
Interannual Variability ◽  
Regional Analysis ◽  
Moisture Flux ◽  
Accurate Estimate ◽  
Flux Divergence ◽  
Vapor Source ◽  
Moisture Fluxes ◽  
Mathematical Algorithms ◽  
Global Reanalysis ◽  
Moisture Flux Divergence

Abstract This study estimates discrepancies in moisture flux divergence in the Intra-Americas Sea (IAS; including the Gulf of Mexico and the Caribbean Sea) calculated using sounding observations, the NCEP Eta high-resolution regional analysis, and the NCEP–NCAR coarse-resolution global reanalysis. The main purpose of this exercise is to quantify the uncertainties in the global reanalysis when it is used to calculate annual and interannual variability of moisture flux divergence in the region. An accurate estimate of moisture flux divergence is crucial to evaluate whether the IAS serves as a water vapor source for rainfall over the adjacent land. Using the three datasets, the uncertainties of calculated moisture flux divergence due to the design of the boundary of the area, mathematical algorithms, and spatial and temporal resolutions are quantified. The results show that the large seasonal and interannual variability in moisture flux divergence estimated using the NCEP–NCAR reanalysis is not compromised by these uncertainties. Therefore, NCEP–NCAR reanalysis, with its global coverage and long-term record, can be used to provide the best estimate of short climate variability of moisture flux divergence available to date. Further comparisons are made of the moisture flux divergence based on the NCEP–NCAR reanalysis with previous estimates using single-year sounding observations, as well as with multiyear estimates based on global datasets of surface evaporation and precipitation. It is shown that the previous estimates using single-year sounding observations bear large uncertainties because of interannual variability. Large uncertainties also exist in datasets of surface global evaporation and precipitation.

A Methodology for the Regional-Scale-Decomposed Atmospheric Water Budget: Application to a Simulation of the Canadian Regional Climate Model Nested by NCEP–NCAR Reanalyses over North America

2006 ◽  
Vol 134 (3) ◽  
pp. 854-873 ◽  
Author(s):  
Soline Bielli ◽  
René Laprise
Keyword(s):  
Regional Climate Model ◽  
Large Scale ◽  
Climate Model ◽  
Spatial Scales ◽  
Regional Climate ◽  
Moisture Flux ◽  
Added Value ◽  
Small Scale ◽  
Flux Divergence ◽  
Moisture Flux Divergence

Abstract The purpose of this work is to study the added value of a regional climate model with respect to the global analyses used to drive the regional simulation, with a special emphasis on the nonlinear interactions between different spatial scales, focusing on the moisture flux divergence. The atmospheric water budget is used to apply the spatial-scale decomposition approach, as it is a key factor in the energetics of the climate. A Fourier analysis is performed individually for each field on pressure levels. Each field involved in the computation of moisture flux divergence is separated into three components that represent selected scale bands, using the discrete cosine transform. The divergence of the moisture flux is computed from the filtered fields. Instantaneous and monthly mean fields from a simulation performed with the Canadian Regional Climate Model are decomposed and allowed to separate the added value of the model to the total fields. Results show that the added value resides in the nonlinear interactions between large (greater than 1000 km) and small (smaller than 600 km) scales. The main small-scale forcing of the wind is topographic, whereas the humidity tends to show more small scales over the ocean. The time-mean divergence of moisture flux is also decomposed into contributions from stationary eddies and transient eddies. Both stationary and transient eddies are decomposed into different spatial scales and show very different patterns. The time-mean divergence due to transient eddies is dominated by large-scale (synoptic scale) features with little small scales. The divergence due to stationary eddies is a combination of small- and large-scale terms, and the main small-scale contribution occurs over the topography. The same decomposition has been applied to the NCEP–NCAR reanalyses used to drive the regional simulation; the results show that the model best reproduces the time-fluctuation component of the moisture flux divergence, with a correlation between the model simulation and the NCEP–NCAR reanalyses above 0.90.

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