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and turbulence, and (iii) the uncertainties associated with the parameterization of radiation transfer and surface–atmosphere interactions. Thus apart from an idealized topography, the setup of the simulations is as close as possible to real-case simulations. The models are run with comprehensive model physics including a radiation transfer scheme, land surface scheme, and turbulence parameterization. A large computational domain and periodic lateral boundary conditions are used in order to
and turbulence, and (iii) the uncertainties associated with the parameterization of radiation transfer and surface–atmosphere interactions. Thus apart from an idealized topography, the setup of the simulations is as close as possible to real-case simulations. The models are run with comprehensive model physics including a radiation transfer scheme, land surface scheme, and turbulence parameterization. A large computational domain and periodic lateral boundary conditions are used in order to
1. Introduction Understanding the winds within a valley and their interactions with the larger-scale forcings is of interest for a number of reasons. For example, the dispersion of pollutants in a valley depends strongly on local valley circulations (e.g., Whiteman 1989 ; Fast et al. 2006 ); nocturnal minimum surface temperatures depend strongly on the near-surface wind speed (e.g., Estournel and Guedalia 1985 ; Steeneveld et al. 2006 ) and hence on the strength of the valley wind; land
1. Introduction Understanding the winds within a valley and their interactions with the larger-scale forcings is of interest for a number of reasons. For example, the dispersion of pollutants in a valley depends strongly on local valley circulations (e.g., Whiteman 1989 ; Fast et al. 2006 ); nocturnal minimum surface temperatures depend strongly on the near-surface wind speed (e.g., Estournel and Guedalia 1985 ; Steeneveld et al. 2006 ) and hence on the strength of the valley wind; land
turbulent interaction between the valley air and the overlying atmosphere ( Figs. 13b , 14 ). The daily maximum mixed-layer depth was calculated according to (5) for the three WRF simulations ( Figs. 11 , 14 ). This gives H ∼ 1600 m and H ∼ 1400 m for the weak and moderate westerly cases as compared with H ∼ 1800 m (with mixed-layer top at 2800 m) for the quiescent case. This agrees with the observational results shown in Fig. 8 . 6. The valley depth and seasonal effects To extend our results
turbulent interaction between the valley air and the overlying atmosphere ( Figs. 13b , 14 ). The daily maximum mixed-layer depth was calculated according to (5) for the three WRF simulations ( Figs. 11 , 14 ). This gives H ∼ 1600 m and H ∼ 1400 m for the weak and moderate westerly cases as compared with H ∼ 1800 m (with mixed-layer top at 2800 m) for the quiescent case. This agrees with the observational results shown in Fig. 8 . 6. The valley depth and seasonal effects To extend our results
1. Introduction Moist processes have been largely ignored in the majority of mountain-wave studies, partially because of the complexity associated with moisture and microphysical processes. Studies of the interaction between moist airflow and mesoscale topography can be broadly classified into two categories. The first category includes quasi-analytical studies with highly simplified representations of moist processes. For example, a set of two-dimensional steady-state linear wave solutions
1. Introduction Moist processes have been largely ignored in the majority of mountain-wave studies, partially because of the complexity associated with moisture and microphysical processes. Studies of the interaction between moist airflow and mesoscale topography can be broadly classified into two categories. The first category includes quasi-analytical studies with highly simplified representations of moist processes. For example, a set of two-dimensional steady-state linear wave solutions
-propagating gravity waves ( Sun et al. 2004 ), turbulence and mean shear interactions ( Nakamura and Mahrt 2005 ), and slope and valley flow transitions ( WHP09 ). Note that except for the last reference, all mechanisms are derived from the Cooperative Atmospheric-Surface Exchange Study -1999 (CASES-99) over nearly flat terrain. In reality, SBL flows are usually affected by the complex land surface. Large-scale topographic features such as mountains and valleys have pronounced effects in stratified flows ( Baines
-propagating gravity waves ( Sun et al. 2004 ), turbulence and mean shear interactions ( Nakamura and Mahrt 2005 ), and slope and valley flow transitions ( WHP09 ). Note that except for the last reference, all mechanisms are derived from the Cooperative Atmospheric-Surface Exchange Study -1999 (CASES-99) over nearly flat terrain. In reality, SBL flows are usually affected by the complex land surface. Large-scale topographic features such as mountains and valleys have pronounced effects in stratified flows ( Baines
is on the regular evening warmings on the floor and sidewalls of the broad Owens Valley, for which the interactions between shallow drainage flows and ambient flows within the bulk of the valley atmosphere become important. 8. Conclusions The normal late afternoon or early evening temperature declines that occur at sites on the valley floor and sidewalls of California’s Owens Valley are often followed by short-lived evening temperature rises. The normal slow nighttime fall of temperature ensues
is on the regular evening warmings on the floor and sidewalls of the broad Owens Valley, for which the interactions between shallow drainage flows and ambient flows within the bulk of the valley atmosphere become important. 8. Conclusions The normal late afternoon or early evening temperature declines that occur at sites on the valley floor and sidewalls of California’s Owens Valley are often followed by short-lived evening temperature rises. The normal slow nighttime fall of temperature ensues
than that in the valley (typically because of daytime solar warming within the valley) and, flowing over the Sierra Nevada, induces downslope winds by undercutting the valley atmosphere. Jiang and Doyle (2008) , in a study of diurnal variation of downslope winds in Owens Valley, demonstrated this effect for the case of only moderate mountaintop winds by using observations and high-resolution modeling, terming the flow “in-valley westerly.” Mayr and Armi (2010) show further evidence from T
than that in the valley (typically because of daytime solar warming within the valley) and, flowing over the Sierra Nevada, induces downslope winds by undercutting the valley atmosphere. Jiang and Doyle (2008) , in a study of diurnal variation of downslope winds in Owens Valley, demonstrated this effect for the case of only moderate mountaintop winds by using observations and high-resolution modeling, terming the flow “in-valley westerly.” Mayr and Armi (2010) show further evidence from T
Schoeberl 1989 ). Mountain waves can have an important impact on the atmosphere because of their role in downslope windstorms ( Klemp and Lilly 1975 ); clear-air turbulence ( Clark et al. 2000 ); vertical mixing of water vapor, aerosols, and chemical constituents in the stratosphere ( Dörnbrack and Dürbeck 1998 ); potential vorticity generation ( Schär and Durran 1997 ); and orographic drag influence on the general circulation ( Bretherton 1969 ; Ólafsson and Bougeault 1996 ). Although numerical models
Schoeberl 1989 ). Mountain waves can have an important impact on the atmosphere because of their role in downslope windstorms ( Klemp and Lilly 1975 ); clear-air turbulence ( Clark et al. 2000 ); vertical mixing of water vapor, aerosols, and chemical constituents in the stratosphere ( Dörnbrack and Dürbeck 1998 ); potential vorticity generation ( Schär and Durran 1997 ); and orographic drag influence on the general circulation ( Bretherton 1969 ; Ólafsson and Bougeault 1996 ). Although numerical models
paper presents a case study of an afternoon downslope westerly wind event documented during the intensive observational period (IOP) 12 of SRP, which took place in Owens Valley from 13 to 17 April 2004. The objective of this study is to examine the diurnal variation of flows in Owens Valley, which involves multiscale interactions among the large-scale westerlies, mountain waves, and differential heating within the boundary layer (BL). Over the past few decades, downslope windstorms and large
paper presents a case study of an afternoon downslope westerly wind event documented during the intensive observational period (IOP) 12 of SRP, which took place in Owens Valley from 13 to 17 April 2004. The objective of this study is to examine the diurnal variation of flows in Owens Valley, which involves multiscale interactions among the large-scale westerlies, mountain waves, and differential heating within the boundary layer (BL). Over the past few decades, downslope windstorms and large
) with thermally driven upvalley and upslope flows ( Fig. 2a ). A transition from a quiescent valley atmosphere to a valley atmosphere affected by mountain-wave activity occurred during midafternoon between 2300 and 0000 UTC ( Fig. 2b ). While southeasterly flow prevailed in the valley center the flow on the western slope became more irregular with downslope winds replacing the upslope winds and colliding with the upvalley flow ( Fig. 2c ). Southeasterly winds up to 15 m s −1 in a layer between 400
) with thermally driven upvalley and upslope flows ( Fig. 2a ). A transition from a quiescent valley atmosphere to a valley atmosphere affected by mountain-wave activity occurred during midafternoon between 2300 and 0000 UTC ( Fig. 2b ). While southeasterly flow prevailed in the valley center the flow on the western slope became more irregular with downslope winds replacing the upslope winds and colliding with the upvalley flow ( Fig. 2c ). Southeasterly winds up to 15 m s −1 in a layer between 400
