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"Decker, Mark"
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Development and evaluation of a new soil moisture and runoff parameterization for the CABLE LSM including subgrid‐scale processes
New conceptual parameterizations of subgrid‐scale soil moisture, runoff generation, and groundwater are developed and tested in the offline version of the Community Atmosphere and Biosphere Land Exchange (CABLE) model. These developments are designed to address a known bias in CABLE: the excess simulation of mean evapotranspiration over most of the Northern Hemisphere and over most vegetation types at global scales. The inclusion of subgrid‐scale soil moisture parameterizations and runoff generation processes largely mitigates the overestimation of evapotranspiration, and simultaneously improves the simulation of mean runoff. There are also pronounced improvements in total water storage anomalies as compared to various observationally derived estimates. It is shown that surface and subsurface runoff generation resulting from subgrid‐scale soil moisture heterogeneity is necessary to accurately simulate the mean observed runoff and evapotranspiration. Surface runoff generation is largely responsible from reducing the mean evapotranspiration bias north of 30°N. We note that the inability of previous CABLE evaluation studies to demonstrate the need for subgrid‐scale heterogeneity is likely due to only testing at flux tower site scales. Evaluating land models at point scale and catchment scale across a large range of climate and vegetation types is necessary to evaluate the contributions of processes that influence the model at various spatial scales. Flux tower data are therefore a necessary but insufficient constraint on land surface models. Key Points: CABLE overestimates mean ET north of 20° Subgrid moisture and runoff generation developed for CABLE New processes drastically improve simulations of ET, Runoff, and SM
Journal Article
Evaluation of the Reanalysis Products from GSFC, NCEP, and ECMWF Using Flux Tower Observations
Reanalysis products produced at the various centers around the globe are utilized formany different scientific endeavors, including forcing land surface models and creating surface flux estimates. Here, flux tower observations of temperature, wind speed, precipitation, downward shortwave radiation, net surface radiation, and latent and sensible heat fluxes are used to evaluate the performance of various reanalysis products [NCEP–NCAR reanalysis and Climate Forecast System Reanalysis (CFSR) from NCEP; 40-yr European Centre for Medium-Range Weather Forecasts (ECMWF) Re-Analysis (ERA-40) and ECMWF Interim Re-Analysis (ERA-Interim) from ECMWF; and Modern-Era Retrospective Analysis for Research and Applications (MERRA) and Global Land Data Assimilation System (GLDAS) from the Goddard Space Flight Center (GSFC)]. To combine the biases and standard deviation of errors from the separate stations, a ranking system is utilized. It is found that ERA-Interim has the lowest overall bias in 6-hourly air temperature, followed closely by MERRA and GLDAS. The variability in 6-hourly air temperature is again most accurate in ERA-Interim. ERA-40 is found to have the lowest overall bias in latent heat flux, followed closely by CFSR, while ERA-40 also has the lowest 6-hourly sensible heat bias. MERRA has the second lowest and is close to ERA-40. The variability in 6-hourly precipitation is best captured by GLDAS and ERA-Interim, and ERA-40 has the lowest precipitation bias. It is also found that at monthly time scales, the bias term in the reanalysis products are the dominant cause of the mean square errors, while at 6-hourly and daily time scales the dominant contributor to the mean square errors is the correlation term. Also, it is found that the hourly CFSR data have discontinuities present due to the assimilation cycle, while the hourly MERRA data do not contain these jumps.
Journal Article
Local land-atmosphere feedbacks limit irrigation demand
Irrigation is known to influence regional climate but most studies forecast and simulate irrigation with offline (i.e. land only) models. Using south eastern Australia as a test bed, we demonstrate that irrigation demand is fundamentally different between land only and land-atmosphere simulations. While irrigation only has a small impact on maximum temperature, the semi-arid environment experiences near surface moistening in coupled simulations over the irrigated regions, a feedback that is prevented in offline simulations. In land only simulations that neglect the local feedbacks, the simulated irrigation demand is 25% higher and the standard deviation of the mean irrigation rate is 60% smaller. These local-scale irrigation-driven feedbacks are not resolved in coarse-resolution climate models implying that use of these tools will overestimate irrigation demand. Future studies of irrigation demand must therefore account for the local land-atmosphere interactions by using coupled frameworks, at a spatial resolution that captures the key feedbacks.
Journal Article
On the use of the GRACE normal equation of inter-satellite tracking data for estimation of soil moisture and groundwater in Australia
An accurate estimation of soil moisture and groundwater is essential for monitoring the availability of water supply in domestic and agricultural sectors. In order to improve the water storage estimates, previous studies assimilated terrestrial water storage variation (ΔTWS) derived from the Gravity Recovery and Climate Experiment (GRACE) into land surface models (LSMs). However, the GRACE-derived ΔTWS was generally computed from the high-level products (e.g. time-variable gravity fields, i.e. level 2, and land grid from the level 3 product). The gridded data products are subjected to several drawbacks such as signal attenuation and/or distortion caused by a posteriori filters and a lack of error covariance information. The post-processing of GRACE data might lead to the undesired alteration of the signal and its statistical property. This study uses the GRACE least-squares normal equation data to exploit the GRACE information rigorously and negate these limitations. Our approach combines GRACE's least-squares normal equation (obtained from ITSG-Grace2016 product) with the results from the Community Atmosphere Biosphere Land Exchange (CABLE) model to improve soil moisture and groundwater estimates. This study demonstrates, for the first time, an importance of using the GRACE raw data. The GRACE-combined (GC) approach is developed for optimal least-squares combination and the approach is applied to estimate the soil moisture and groundwater over 10 Australian river basins. The results are validated against the satellite soil moisture observation and the in situ groundwater data. Comparing to CABLE, we demonstrate the GC approach delivers evident improvement of water storage estimates, consistently from all basins, yielding better agreement on seasonal and inter-annual timescales. Significant improvement is found in groundwater storage while marginal improvement is observed in surface soil moisture estimates.
Journal Article
New turbulent resistance parameterization for soil evaporation based on a pore‐scale model: Impact on surface fluxes in CABLE
The Community Atmosphere Biosphere Land Exchange (CABLE) land surface model overestimates evapotranspiration (E) at numerous flux tower sites during boreal spring. The overestimation of E is not eliminated when the nonlinear dependence of soil evaporation on soil moisture or a simple litter layer is introduced into the model. New resistance terms, previously developed from a pore‐scale model of soil evaporation, are incorporated into the treatment of under canopy water vapor transfer in CABLE. The new resistance terms reduce the large positive bias in spring time E at multiple flux tower sites and also improve the simulation of daily sensible heat flux. The reduction in the spring E bias allows the soil to retain water into the summer, improving the seasonality of E. The simulation of daily E is largely insensitive to the details of the implementation of the pore model resistance scheme. The more physically based treatment of soil evaporation presented here eliminates the need for empirical functions that reduce evaporation as a function of soil moisture that are included in many land surface models. Key Points CABLE overestimates spring time ET at many flux tower sites Resistance to soil evaporation defined with a pore‐scale model of evaporation New formulation reduces bias and root mean square errors, particularly in spring Pore model parameterizations enhance transpiration relative to soil evaporation
Journal Article
Improving the Numerical Solution of Soil Moisture–Based Richards Equation for Land Models with a Deep or Shallow Water Table
The soil moisture–based Richards equation is widely used in land models for weather and climate studies, but its numerical solution using the mass-conservative scheme in the Community Land Model is found to be deficient when the water table is within the model domain. Furthermore, these deficiencies cannot be reduced by using a smaller grid spacing. The numerical errors are much smaller when the water table is below the model domain. These deficiencies were overlooked in the past, most likely because of the more dominant influence of the free drainage bottom boundary condition used by many land models. They are fixed here by explicitly subtracting the hydrostatic equilibrium soil moisture distribution from the Richards equation. This equilibrium distribution can be derived at each time step from a constant hydraulic (i.e., capillary plus gravitational) potential above the water table, representing a steady-state solution of the Richards equation. Furthermore, because the free drainage condition has serious deficiencies, a new bottom boundary condition based on the equilibrium soil moisture distribution at each time step is proposed that also provides an effective and direct coupling between groundwater and surface water.
Journal Article
(Re)Model(ed) Towns and the Remodeling of American Ideology: The Expansion of Middle-Class Hegemony in Allan Pinkerton's The Model Town and the Detectives and Dashiell Hammett's Red Harvest
Because their texts reflect their culture's desire to see America as a middle-class society, Pinkerton and Hammett implicitly argue that the middle class should provide the \"moral and cultural leadership\" that Antonio Gramsci calls hegemony.3 Hegemony means that a given class can control the master metaphors through which a nation conceptualizes itself. According to Pinkerton, the village was a model because \"the citizens were generally of the more respectable class of society, and the appearance of the town was evidence of a high state of thriftand prosperity\" (21). [...]they saw themselves as developing a \"habitual resort to terms of measurable cause and effect\" combined with \"skepticism of what is only conventionally valid\"; these attributes are the sine qua non of the trained expert (Veblen, Theory 309 -10, 323). According to Erin Smith, fans of the Op stories were \"white, working-class men\" who equated practical training with economic and social advancement (10; 11).
Journal Article
Use of a sliding plate rheometer to measure the first normal stress difference at high shear rates
The use of a sliding plate rheometer (SPR) to determine the first normal stress difference of molten polymers and elastomers at high shear rates is demonstrated. The simple shear flow in this instrument is not subject to the flow instabilities that limit the use of rotational rheometers to shear rates often below 1 s−1. However, issues of secondary flow and wall slip must be addressed to obtain reliable data using an SPR. A highly entangled, monodisperse polybutadiene and a commercial polystyrene were the polymers studied. The inclusion of the polystyrene made it possible to compare data with those obtained by Lodge using a stressmeter, which is an instrument based on the measurement of the hole pressure. The data from the two instruments are in good agreement and are also close to the predictions of an empirical equation of Laun based on the storage and loss moduli.
Journal Article
From Bad Boys to Good Managers: Twain, Aldrich, and the Creation of a Middle-Class Ideal
[...]Alan Gribben argues that The Story of a Bad Boy represents \"the standard work\" that Twain \"tried to surpass\" (158).Because of this obvious resemblance, most critics who discuss the similarities between Aldrich's and Twain's books are interested in positioning them as ideal types of the Bad Boy genre, then using those books to help explain that genre.1 Mary Lystad, for example, has shown that both novels privilege the boy's peer group over his family (68).Furthermore, he always knows what \"[is] expected of\" him and prides himself on his ability to \"always be on time\" (On Time 142).Because of these qualities, Wolf eventually convinces the rival owners of a passenger steamboat line and a railroad that combining their services \"would be a benefit to the travelling public, while it would afford a remunerative business to each line\" (Brake 15).Desiring to give the town \"a broadside,\" they organize themselves and work diligently to remount and clean the heavy guns.Since one boy buying several pounds of gunpowder would be suspicious, they divide into teams of four so that individual members can purchase small amounts of gunpowder from assigned stores until they have enough to fire the cannons (207, 209).Fortunately for Aunt Sally and Uncle Silas, Tom has been summoned before Jake's death and is able to deduce what really happened.Since Brace gets much closer to realizing his plan than do the criminal gangs of Mariola, however, Detective Tom becomes Counselor Sawyer.
Journal Article