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Sujay V. Kumar, Rolf H. Reichle, Randal D. Koster, Wade T. Crow, and Christa D. Peters-Lidard

1. Introduction Soil moisture (sm) plays an important role in controlling evaporation, plant transpiration, infiltration, and runoff, and consequently in modulating the partitioning of water and energy fluxes across the land–atmosphere interface. Moreover, root-zone soil moisture provides a critical memory function in the climate system at monthly time scales. Characterization of soil moisture in the root zone is therefore important for many applications, including agricultural and water

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Richard J. Ellis, Christopher M. Taylor, Graham P. Weedon, Nicola Gedney, Douglas B. Clark, and Sietse Los

1. Introduction General circulation models (GCMs) constrain the surface moisture flux between land and atmosphere with some representation of soil moisture. Manabe (1969) modified evaporation using a simple ratio between soil moisture and a critical soil moisture (0.75 of the field capacity). Since this rather simple approach for representing soil moisture control of evaporation, a number of models with different levels of complexity have evolved, including Milly and Shmakin (2002) , Dai et

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Lucas R. Vargas Zeppetello, David S. Battisti, and Marcia B. Baker

due to the complexity of land–atmosphere interaction no singular cause has been identified. However, model representations of evaporation have been implicated as a primary cause of temperature biases in climate models ( Mueller and Seneviratne 2014 ; Merrifield and Xie 2016 ; Ma et al. 2018 ). Variations in evaporation are linked to variations in soil moisture, which has become widely regarded as a fundamental control on summertime temperatures ( Seneviratne et al. 2010 ). While current

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Yeonjoo Kim and Guiling Wang

1. Introduction Soil moisture–precipitation coupling may result in persistence of climate anomalies, making soil moisture a potentially useful predictor in seasonal predictions. The slowly varying soil moisture records past and present precipitation anomalies; as the resulting soil moisture feeds back to influence precipitation, this may lead to the persistence of soil moisture and precipitation anomalies. Where vegetation growth is limited by water, this soil moisture–precipitation coupling is

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Bruce T. Anderson, Alex C. Ruane, John O. Roads, and Masao Kanamitsu

, resulting in dry winters and wet summers ( Douglas et al. 1993 ). To the east over the Great Plains, precipitation tends to be low (when compared with the western and eastern coastal regions), particularly during winter, as dry air descends into the region from the Rocky Mountain plateau; however, in spring and summertime a strong low-level jet draws moisture into the continental interior from the Gulf of Mexico ( Higgins et al. 1997b ), feeding convective storms as they propagate from the lee of the

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Samar Minallah and Allison L. Steiner

1. Introduction Precipitation is a principal component in the land and atmospheric moisture budgets, regulating the water availability and quality in the Great Lakes watersheds and various processes including surface runoff, lake levels, soil moisture, and groundwater reserves. It is affected both by local feedback mechanisms—that is, regional evapotranspiration resulting in recycled precipitation ( Dominguez et al. 2006 ; Lamb et al. 2012 )—and large-scale processes in the form of atmospheric

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Vahid Naeimi, Zoltan Bartalis, and Wolfgang Wagner

1. Introduction Microwave sensors on board remote sensing satellites offer an attractive and relatively direct way of measuring soil moisture, thanks to the strong relationship between soil moisture content and the soil dielectric constant. In contrast to pointwise in situ measurements, satellite-borne instruments delivering measurements integrated over larger areas are better suited for hydrological studies of entire catchments or geographical regions. Yet to date, because of the complexity of

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Ruzbeh Akbar, Daniel J. Short Gianotti, Kaighin A. McColl, Erfan Haghighi, Guido D. Salvucci, and Dara Entekhabi

1. Introduction The profile of soil moisture—from surface to root zone—partially determines water and heat fluxes between the land and atmosphere depending on the dominant evapotranspiration regime ( Seneviratne et al. 2010 ), affects the dynamics of soil respiration ( Manzoni et al. 2012 ), and drives the growth of crops and natural vegetation ( Rosenzweig et al. 2002 ). Weather forecasting and climate modeling efforts, especially at large spatial scales, have long been recognized to require

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Tiina Nygård, Rune G. Graversen, Petteri Uotila, Tuomas Naakka, and Timo Vihma

1. Introduction Atmospheric moisture and clouds play a central role in radiative processes ( Morrison et al. 2012 ) and the hydrological cycle ( Vihma et al. 2016 ) in the Arctic. Through radiation, clouds and atmospheric moisture regulate the surface energy balance and surface temperature. For most of the year, including winter, clouds have a warming impact on the surface because they reduce the surface energy loss by reemitting longwave radiation back to the surface ( Shupe and Intrieri 2004

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Larry K. Berg, Laura D. Riihimaki, Yun Qian, Huiping Yan, and Maoyi Huang

1. Introduction and motivation It is well recognized that the southern Great Plains (SGP) low-level jet (LLJ) plays an important role in the regional-scale moisture transport over the central United States (e.g., Uccellini and Johnson 1979 ; Helfand and Schubert 1995 ; Stensrud 1996 ; Higgins et al. 1997 ; Schubert et al. 1998 ; Tollerud et al. 2008 ; Frye and Mote 2010 ). A number of different mechanisms have been suggested as the cause of LLJs, as highlighted by Kraus et al. (1985

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