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A. Gettelman and Q. Fu

1. Introduction The largest uncertainty in predicting the future state of the atmosphere lies in properly estimating the internal changes to the climate system in response to a radiative perturbation ( Cess et al. 1989 ; Cess 2005 ). The impact of these internal changes, commonly called feedbacks on the climate system, can be as large as the primary forcing signal. Perhaps the most important feedback in the earth’s climate system is the climate feedback due to upper-tropospheric water vapor (H

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J. M. Livingston, B. Schmid, P. B. Russell, J. R. Podolske, J. Redemann, and G. S. Diskin

1. Introduction Water vapor measurements by sun photometry using the 940-nm water vapor absorption band have been compared to in situ and other remote (e.g., microwave) measurements in several previous publications (e.g., Schmid et al. 2000 , 2001 , 2003a , b , 2006 ; Redemann et al. 2003 ; Livingston et al. 2000 , 2003 , 2007 ). Those comparisons were all restricted to sun photometer altitudes <∼6 km, with water vapor columns ∼0.1 to 5 g cm −2 , and water vapor densities ∼0.1 to 17 g

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Will Cantrell, Eli Ochshorn, Alexander Kostinski, and Keith Bozin

1. Introduction Below the melting point, the equilibrium vapor pressure (hereafter referred to simply as vapor pressure) of liquid water exceeds that of ice at the same temperature. Because of that difference in vapor pressure, in clouds, once any droplet freezes, it grows by condensation at the expense of surrounding droplets that have not frozen. To calculate the rate at which the mass transfer proceeds, both vapor pressures must be known as it is the difference (i.e., gradient) that drives

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Alexander Haefele and Niklaus Kämpfer

1. Introduction Water vapor is the most important natural greenhouse gas of the atmosphere and has a large impact on its radiative properties and hence on its thermodynamic balance. Despite the importance of water vapor in the climate system and weather forecasting, there is no technique available, neither ground-based nor spaceborne, that can provide continuous measurements of the humidity profile under all weather conditions. Ground-based microwave radiometers measuring the pressure

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Christopher E. Holloway and J. David Neelin

1. Introduction A number of studies indicate that moist convection is sensitive to free-tropospheric water vapor, including observational analyses ( Austin 1948 ; Malkus 1954 ; Brown and Zhang 1997 ; Sherwood 1999 ; Parsons et al. 2000 ; Bretherton et al. 2004 ; Sherwood et al. 2004 ) and studies using cloud-system-resolving models (CSRMs; Tompkins 2001b ; Grabowski 2003 ; Derbyshire et al. 2004 ). This dependence is apparently not well represented in global climate models ( Derbyshire

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Ronald B. Smith and Jason P. Evans

earth. The range is relatively narrow and oriented perpendicular to the flow. The zone would undoubtedly make an excellent ‘laboratory’ for the verification of theoretical models of airflow over mountain and the resulting precipitation and cloudiness patterns.” The goal of this study is to determine the isotope fractionation of water vapor crossing the southern Andes and to use this information to estimate the drying ratio and test and calibrate a physical model of orographic precipitation. Because

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David N. Whiteman, Kurt Rush, Igor Veselovskii, Martin Cadirola, Joseph Comer, John R. Potter, and Rebecca Tola

1. Introduction Raman lidar is now regarded as one of the leading technologies for atmospheric profiling of water vapor ( Melfi et al. 1989 ; Whiteman et al. 1992 ; Goldsmith et al. 1998 ; Turner et al. 2000 ), cirrus clouds ( Ansmann et al. 1992a ; Reichardt et al. 2002 ; Whiteman et al. 2004 ), aerosols ( Ansmann et al. 1990 ; Ferrare et al. 2006 ), temperature ( Arshinov et al. 2005 ; Behrendt et al. 2002 ; Di Girolamo et al. 2004 ), and other atmospheric constituents or properties

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A. Verhoef, A. Diaz-Espejo, J. R. Knight, L. Villagarcía, and J. E. Fernández

1. Introduction A gain of water in the soil surface layer, not caused by rainfall or irrigation, can be caused by dew deposition or vapor adsorption. Dew deposition is a phenomenon recorded for most soil and climate types ( Jacobs et al. 1994 , 1999 ). It occurs during the night when dewpoint is reached, and it results in a discernable wetting of the surface ( Monteith 1957 ). Vapor adsorption is an important phenomenon in arid and semiarid regions ( Kosmas et al. 1998 , 2001 ; Agam and

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Amin R. Nehrir, Kevin S. Repasky, John L. Carlsten, Michael D. Obland, and Joseph A. Shaw

1. Introduction Water vapor in the lower troposphere plays an important role in many earth system processes associated with the radiation budget and climate, moisture transport and the hydrologic cycle, and weather ( Trenberth et al. 2007 ; Dabberdt and Schlatter 1996 ). Water vapor is primarily contained within the lowest 3 km of the troposphere with high temporal and spatial fluxes ( Dabberdt and Schlatter 1996 ; Weckwerth et al. 1999 ). Radiosonde launches are currently used to obtain

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De-Zheng Sun, Yongqiang Yu, and Tao Zhang

1. Introduction Water vapor provides most of the greenhouse effect of the earth’s atmosphere. Clouds are a major contributor to the planetary albedo ( Kiehl and Trenberth 1997 ). A small change in these radiative effects of water vapor and clouds can either offset or greatly amplify the perturbation to the earth’s radiation balance from anthropogenic effects ( Houghton et al. 2001 ). Therefore, it is imperative for climate models on which our economical polices are increasingly relying to

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