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John D. Hottenstein, Guillermo E. Ponce-Campos, Julio Moguel-Yanes, and M. Susan Moran

1. Introduction Soil moisture plays an integral role within the hydrologic cycle as a critical link between soils, climate, and biogeography ( Legates et al. 2011 ). Soil moisture has been shown to influence soil respiration ( Geng et al. 2012 ), act as a thermal reservoir that impacts cloud formation and wind fields ( Ek and Holtslag 2004 ; Findell and Eltahir 2003 ; Entekhabi et al. 1996 ), and directly influence precipitation formation ( Koster et al. 2004 ). As the understanding of the

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Robert M. Parinussa, Thomas R. H. Holmes, Niko Wanders, Wouter A. Dorigo, and Richard A. M. de Jeu

satellite. In contrast to the polar-orbiting Aqua and GCOM-W1 satellites, TRMM is in near-equatorial orbit. A result of these divergent orbit types is that the TMI record overlaps with both AMSR sensors at recurring times within their respective observation periods. A downside of the TMI sensor compared to the others (AMSR-E and AMSR2) is the lack of observations in the low C-band frequency, as these observations have the most sensitivity to soil moisture. Here, we aim for consistency between

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Russ S. Schumacher and Thomas J. Galarneau Jr.

1. Introduction Recent studies have analyzed regions of heavy rainfall that occur ahead of recurving tropical cyclones (TCs), in which tropical moisture transported ahead of the TC enhances the precipitation in midlatitude convective systems ( Wang et al. 2009 ; Galarneau et al. 2010 ; Schumacher et al. 2011 ). These situations were termed predecessor rain events (PREs) by Galarneau et al. (2010) . PREs occur when tropical moisture is transported poleward of the TC and is lifted along a low

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Paul A. O’Gorman and Tapio Schneider

1. Introduction Studies of the Lagrangian moisture transport suggest that, sufficiently far away from regions of moist convection, large-scale processes significantly influence the relative humidity of the free troposphere. (e.g., Yang and Pierrehumbert 1994 ; Sherwood 1996 ; Salathé and Hartmann 1997 ; Pierrehumbert and Roca 1998 ; Dessler and Sherwood 2000 ). Galewsky et al. (2005) have shown that large-scale aspects of the relative humidity distribution in the free troposphere can be

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Yanhong Gao, Lan Cuo, and Yongxin Zhang

1. Introduction Moisture is one of the most critical components of the hydrological cycle, and changes in moisture reflect shifts in the controlling atmospheric circulations and (or) underlying surface, with profound implications for weather and climate. As climate change is taking place as a result of the emissions of greenhouse gases and aerosols ( Solomon et al. 2007 ), one important question to ask is to what degree climate change will affect moisture changes or, in other words, how

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Zhengyu Liu

forcing in the presence of a long soil moisture memory. This type of abrupt change in a monostable system, known as the stable collapse, is in contrast to the classical mechanism of abrupt change in a bistable climate–ecosystem ( Claussen et al. 1999 ) and other climate systems (e.g., Cessi 1994 ; Timmermann and Lohmann 2000 ). However, LIU only presented a few examples of the abrupt changes in a monostable system. It remains unclear what mechanism is responsible for this abrupt change and how the

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Joaquín Muñoz Sabater, Lionel Jarlan, Jean-Christophe Calvet, François Bouyssel, and Patricia De Rosnay

1. Introduction The accuracy of short-term to seasonal weather predictions depends on a good initialization of several surface variables of slow variation in the coupled land surface–atmosphere system. Among these variables, root-zone soil moisture is of prime importance. Root-zone soil moisture plays a vital role in the regulation of water and energy budgets at the soil–vegetation–atmosphere interface through evaporation processes of the uppermost surface soil layer and plant transpiration

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Sujay V. Kumar, Christa D. Peters-Lidard, David Mocko, Rolf Reichle, Yuqiong Liu, Kristi R. Arsenault, Youlong Xia, Michael Ek, George Riggs, Ben Livneh, and Michael Cosh

1. Introduction Drought is one of the costliest environmental disasters and has profound socioeconomic consequences, as it typically occurs at long time scales and in virtually all climatic zones. Droughts are generally classified into three physical types: meteorological drought resulting from precipitation deficits, agricultural drought due to total soil moisture deficits, and hydrological drought related to the shortage of streamflow or runoff ( Keyantash and Dracup 2002 ; Mo 2008 ; Shukla

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Robin Chadwick, Peter Good, and Kate Willett

1. Introduction Future changes in surface humidity under global warming could affect human comfort ( Willett and Sherwood 2012 ), labor capacity ( Dunne et al. 2013 ), and even, for extreme warming scenarios, the habitability of some land regions ( Sherwood and Huber 2010 ; Pal and Eltahir 2016 ). Humidity changes are also closely linked to changes in surface evaporation, transpiration, soil moisture, mean and extreme precipitation, and clouds (e.g., Emori and Brown 2005 ; Fasullo 2012

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Adriaan J. Teuling, Remko Uijlenhoet, Bart van den Hurk, and Sonia I. Seneviratne

1. Introduction The dynamic role of the land surface in the climate system is nowadays widely recognized. Fluxes of latent heat from the land surface into the atmosphere transport large amounts of energy and water and limit direct heating of the lower atmosphere. Their magnitude, however, strongly depends on the soil moisture content of the soil. Model studies have shown that without soil moisture interacting freely with the atmosphere, warm season precipitation and temperature variability over

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