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Eui-Seok Chung and Brian J. Soden

1. Introduction It is well known that better understanding of characteristics of upper-tropospheric water vapor (UTWV) is an essential part in the prediction of future climate ( Held and Soden 2000 ). Since the trapping of longwave radiation is proportional to the logarithm of water vapor concentration, small spatiotemporal changes in water vapor in the upper troposphere can have a significant radiative impact (e.g., Sohn and Schmetz 2004 ). Thus, various in situ and remote sensing instruments

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Rosario Q. Iannone, Daniele Romanini, Samir Kassi, Harro A. J. Meijer, and Erik R. Th Kerstel

1. Introduction Water vapor is a key element in the global climate, as it is the most active greenhouse gas. In the troposphere, water is responsible for the global movement of latent heat and it affects cloud cover, which controls radiation and cooling rates. In the stratosphere, water vapor affects ozone levels through its involvement in the production of odd-hydrogen and the formation of stratospheric clouds ( Kirk-Davidoff et al. 1999 ; Forster and Shine 2002 ). In situ measurements of

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Luke Oman, Darryn W. Waugh, Steven Pawson, Richard S. Stolarski, and J. Eric Nielsen

, H. , S. Solomon , and R. R. Garcia , 1988 : The role of molecular hydrogen and methane oxidation in the water vapour budget of the stratosphere. Quart. J. Roy. Meteor. Soc. , 114 , 281 – 295 . Oltmans , S. J. , H. Vömel , D. J. Hofmann , K. Rosenlof , and D. Kley , 2000 : The increase in stratospheric water vapor from balloon borne frostpoint hygrometer measurements at Washington, D.C. and Boulder, Colorado. Geophys. Res. Lett. , 27 , 3453 – 3456 . Pawson , S

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Andreas Behrendt, Volker Wulfmeyer, Hans-Stefan Bauer, Thorsten Schaberl, Paolo Di Girolamo, Donato Summa, Christoph Kiemle, Gerhard Ehret, David N. Whiteman, Belay B. Demoz, Edward V. Browell, Syed Ismail, Richard Ferrare, Susan Kooi, and Junhong Wang

airborne DIAL. J. Geophys. Res. , 104 , 31351 – 31359 . 10.1029/1999JD900959 Ferrare, R. A. , and Coauthors , 2002 : Characterization of upper troposperic water vapour measurements during AFWEX using LASE. Proc. 21st ILRC, Lidar Remote Sensing in Atmospheric and Earth Sciences, Vol. I, Quebec, Canada, Defense R&D Canada-Valcartier, 397–400 . Ferrare, R. A. , and Coauthors , 2004 : Characterization of upper-troposphere water vapor measurements during AFWEX using LASE. J. Atmos. Oceanic

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H. Vömel, V. Yushkov, S. Khaykin, L. Korshunov, E. Kyrö, and R. Kivi

1. Introduction Upper-tropospheric and stratospheric water vapor plays an important role in the global climate system, yet there are few measurements of this trace gas in this altitude region. Global measurements can be obtained from satellite sensors but require in situ measurements for validation and often have limited vertical resolution, which is insufficient for process studies within the tropopause region. Only a few instruments are capable of providing reliable in situ observations in

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K. E. Cady-Pereira, M. W. Shephard, D. D. Turner, E. J. Mlawer, S. A. Clough, and T. J. Wagner

1. Introduction Water vapor is the most abundant and the most highly variable greenhouse gas in the atmosphere. This temporal and spatial variability greatly affects the radiative fluxes at the surface and at the top of the atmosphere (TOA) and on the radiative heating rates at all layers of the atmosphere. In addition, the distribution of water vapor is a fundamental driving force behind the formation of clouds and precipitation. The pivotal importance of water vapor to these atmospheric

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Biao Wang, Teruyuki Nakajima, and Guangyu Shi

1. Introduction Climate change can be considered the response of the climate system to external forcings, such as radiative forcing resulting from greenhouse gases (GHGs), atmospheric aerosols, etc. While the understanding of the external forcings remains with uncertainties, the response of the system is largely complicated by a variety of feedback processes, especially those involving clouds and water vapor (CWV) in the atmosphere. Water vapor is an important greenhouse gas and clouds have a

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Ivan Mammarella, Samuli Launiainen, Tiia Gronholm, Petri Keronen, Jukka Pumpanen, Üllar Rannik, and Timo Vesala

measure carbon dioxide and water vapor fluxes between the biosphere and the atmosphere. The advantages of the closed-path setups include low maintenance efforts and costs, long-term stability, and good accuracy. However, the measured fluxes need to be corrected in order to minimize any systematic error arising from the EC system setup and flux-averaging methodology ( Aubinet et al. 2000 ). The underestimation of the EC fluxes due to the system characteristics results from the physical limitations in

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M. Adam, B. B. Demoz, D. D. Venable, E. Joseph, R. Connell, D. N. Whiteman, A. Gambacorta, J. Wei, M. W. Shephard, L. M. Miloshevich, C. D. Barnet, R. L. Herman, and J. Fitzgibbon

1. Introduction Water vapor is an important constituent of the atmosphere. The vertical distribution of moisture is important in determining atmospheric stability. Water vapor is also the most radiatively active atmospheric trace gas in the infrared ( Ramanathan 1988 ) and thus could produce strong forcing from feedback associated with anthropogenically driven climate change ( Cess et al. 1990 ). In addition, there is significant variability in the distribution of water vapor on temporal and

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F. Couvreux, F. Guichard, P. H. Austin, and F. Chen

1. Introduction Water vapor variability was the main focus of the International H 2 O Project (IHOP_2002), which took place in May–June 2002 over the southern Great Plains of the United States ( Weckwerth et al. 2004 ). This field project gathered together most of the techniques for measuring water vapor. We address water vapor variability at the mesoscale (scales larger than thermals, ranging from tens to a few hundreds of kilometers). Comparatively few investigations have considered this

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