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1. Introduction The complex interaction of water vapor with atmospheric motion and mixing processes over a wide range of spatial scales, together with various sinks and sources, leads to a very heterogeneous humidity distribution in the troposphere. A better understanding of the spatial variability of water vapor in the free troposphere is essential for the representation of clouds, including fractional cloud cover, in numerical weather prediction models (NWP) and global circulation models (GCM
1. Introduction The complex interaction of water vapor with atmospheric motion and mixing processes over a wide range of spatial scales, together with various sinks and sources, leads to a very heterogeneous humidity distribution in the troposphere. A better understanding of the spatial variability of water vapor in the free troposphere is essential for the representation of clouds, including fractional cloud cover, in numerical weather prediction models (NWP) and global circulation models (GCM
; Wernli and Davies 1997 ). The boundary layer humidity in the inflow of WCBs (region 1 in Fig. 1 ) can impact the outflow height of WCBs ( Schäfler and Harnisch 2015 ). For some WCBs, the inflow region coincides with a filament of strong horizontal water vapor transport, a so-called atmospheric river, which can contribute to intense rain in the midlatitudes ( Lavers and Villarini 2013 ). During the ascent of WCBs (region 2 in Fig. 1 ), embedded convection, and turbulent fluxes influence the level of
; Wernli and Davies 1997 ). The boundary layer humidity in the inflow of WCBs (region 1 in Fig. 1 ) can impact the outflow height of WCBs ( Schäfler and Harnisch 2015 ). For some WCBs, the inflow region coincides with a filament of strong horizontal water vapor transport, a so-called atmospheric river, which can contribute to intense rain in the midlatitudes ( Lavers and Villarini 2013 ). During the ascent of WCBs (region 2 in Fig. 1 ), embedded convection, and turbulent fluxes influence the level of
Aerosol Effects on Clouds and Precipitation over Central Europe in Different Weather Regimes.g., Cohard and Pinty 2000 ; Milbrandt and Yau 2005 ; Morrison et al. 2009 ; Dipankar et al. 2015 ), the COSMO model uses a saturation adjustment instead of saturation prediction. As was stated by Seifert and Beheng (2006a) , all clouds, except extremely maritime ones, relax rapidly to the thermodynamic equilibrium between water vapor and water drops so that applying the standard saturation adjustment technique to treat condensational growth seems to be appropriate in almost all cases. However, recent
.g., Cohard and Pinty 2000 ; Milbrandt and Yau 2005 ; Morrison et al. 2009 ; Dipankar et al. 2015 ), the COSMO model uses a saturation adjustment instead of saturation prediction. As was stated by Seifert and Beheng (2006a) , all clouds, except extremely maritime ones, relax rapidly to the thermodynamic equilibrium between water vapor and water drops so that applying the standard saturation adjustment technique to treat condensational growth seems to be appropriate in almost all cases. However, recent
, 30 , 3999 – 4020 , https://doi.org/10.1175/JCLI-D-16-0788.1 . 10.1175/JCLI-D-16-0788.1 Schreck , C. J. , L. Shi , J. P. Kossin , and J. J. Bates , 2013 : Identifying the MJO, equatorial waves, and their impacts using 32 years of HIRS upper-tropospheric water vapor . J. Climate , 26 , 1418 – 1431 , https://doi.org/10.1175/JCLI-D-12-00034.1 . 10.1175/JCLI-D-12-00034.1 Sinclaire , Z. , A. Lenouo , C. Tchawoua , and S. Janicot , 2015 : Synoptic Kelvin type perturbation
, 30 , 3999 – 4020 , https://doi.org/10.1175/JCLI-D-16-0788.1 . 10.1175/JCLI-D-16-0788.1 Schreck , C. J. , L. Shi , J. P. Kossin , and J. J. Bates , 2013 : Identifying the MJO, equatorial waves, and their impacts using 32 years of HIRS upper-tropospheric water vapor . J. Climate , 26 , 1418 – 1431 , https://doi.org/10.1175/JCLI-D-12-00034.1 . 10.1175/JCLI-D-12-00034.1 Sinclaire , Z. , A. Lenouo , C. Tchawoua , and S. Janicot , 2015 : Synoptic Kelvin type perturbation
advected westward along the coast and then over land around the mountains of the Kii Peninsula ( Fig. 7a ; the names of topographic locations are given in Fig. 1 ). Nevertheless, they are forced to rise over local hills ( Fig. 8a ; t = −3 to t = 0). There is still an increase in water vapor from evaporating precipitation ( Fig. 8c ), which is now associated with Sinlaku’s principal rainband that propagated over the Kii Peninsula (red line in Fig. 7b ). Despite evaporation, the air parcels
advected westward along the coast and then over land around the mountains of the Kii Peninsula ( Fig. 7a ; the names of topographic locations are given in Fig. 1 ). Nevertheless, they are forced to rise over local hills ( Fig. 8a ; t = −3 to t = 0). There is still an increase in water vapor from evaporating precipitation ( Fig. 8c ), which is now associated with Sinlaku’s principal rainband that propagated over the Kii Peninsula (red line in Fig. 7b ). Despite evaporation, the air parcels
. Geophys. , 20 , 851 – 875 , doi: 10.1029/RG020i004p00851 . Muller , C. J. , L. E. Back , P. A. O’Gorman , and K. A. Emanuel , 2009 : A model for the relationship between tropical precipitation and column water vapor . Geophys. Res. Lett. , 36 , L16804 , doi: 10.1029/2009GL039667 . Plant , R. , and G. Craig , 2008 : A stochastic parameterization for deep convection based on equilibrium statistics . J. Atmos. Sci. , 65 , 87 – 105 , doi: 10.1175/2007JAS2263.1 . Raschendorfer
. Geophys. , 20 , 851 – 875 , doi: 10.1029/RG020i004p00851 . Muller , C. J. , L. E. Back , P. A. O’Gorman , and K. A. Emanuel , 2009 : A model for the relationship between tropical precipitation and column water vapor . Geophys. Res. Lett. , 36 , L16804 , doi: 10.1029/2009GL039667 . Plant , R. , and G. Craig , 2008 : A stochastic parameterization for deep convection based on equilibrium statistics . J. Atmos. Sci. , 65 , 87 – 105 , doi: 10.1175/2007JAS2263.1 . Raschendorfer
frontal type, convection plays an important role in tracer transport. In section 6 we investigated the impact of diabatic heating on potential temperature and PV during the ascent. A larger increase in potential temperature was found in the convective cases (about 28 K), compared to the nonconvective cases (about 20 K), which correlates with the water vapor content in the inflow air mass. In all cases average PV increases below the maximum of latent heating and decreases above, resulting in a PV
frontal type, convection plays an important role in tracer transport. In section 6 we investigated the impact of diabatic heating on potential temperature and PV during the ascent. A larger increase in potential temperature was found in the convective cases (about 28 K), compared to the nonconvective cases (about 20 K), which correlates with the water vapor content in the inflow air mass. In all cases average PV increases below the maximum of latent heating and decreases above, resulting in a PV
deserves attention. Considering the important contribution of diabatic processes to the amplification of the downstream midlatitude RWP during ET, the increasing availability of water vapor in a changing climate suggests that an associated increase in latent heat release may strengthen impacts such as downstream ridge amplification. Research is needed to address this question and to explore how this extreme form of tropical–extratropical interaction could change with a changing climate. Acknowledgments
deserves attention. Considering the important contribution of diabatic processes to the amplification of the downstream midlatitude RWP during ET, the increasing availability of water vapor in a changing climate suggests that an associated increase in latent heat release may strengthen impacts such as downstream ridge amplification. Research is needed to address this question and to explore how this extreme form of tropical–extratropical interaction could change with a changing climate. Acknowledgments
the large vertical gradient of water vapor in the tropopause region implies large gradients in radiative cooling ( Zierl and Wirth 1997 ). Chagnon and Gray (2015) hypothesized that radiative processes thereby influence the propagation of Rossby waves even on the weather time scale. Based on idealized models, it was shown that a sharper waveguide is associated with a faster phase speed ( Harvey et al. 2016 ). More generally, longwave radiative cooling has been demonstrated to substantially modify
the large vertical gradient of water vapor in the tropopause region implies large gradients in radiative cooling ( Zierl and Wirth 1997 ). Chagnon and Gray (2015) hypothesized that radiative processes thereby influence the propagation of Rossby waves even on the weather time scale. Based on idealized models, it was shown that a sharper waveguide is associated with a faster phase speed ( Harvey et al. 2016 ). More generally, longwave radiative cooling has been demonstrated to substantially modify
