Search

A field campaign in a valley near Seefeld, Austria, well known for the frequent occurrence of cold‐air pools, was conducted to identify the processes leading to the formation and erosion of the cold‐air pool. Here, we focus on a case study in January 2020 that featured cold‐air pool formation interrupted by a wind disturbance. Simulations with the Weather Research and Forecasting model were performed at a horizontal grid spacing of 40 m and compared with measurement results. The model was able to reproduce the intense cooling in the beginning of the night and the cold‐air pool erosion in the middle of the night caused by the wind disturbance, but stronger winds than observed prevented the cold‐air pool from fully re‐establishing in the model after the disturbance. The dominant cooling processes were long‐wave radiative heat loss and turbulent exchange, both of which are parametrized and cool the air locally. Advection was the most important warming contribution during the cold‐air pool disturbances, especially its cross‐valley and vertical components. Owing to numerical constraints and the shallow nature of the cold‐air pool, its extent was limited to the lowest model level. Further improvements to the cold‐air pool's representation in the model would require a finer grid resolution. [ABSTRACT FROM AUTHOR]

METEX21 was an atmospheric tracer release experiment executed at the Department of Energy's Nevada National Security Site (NNSS) in the southwestern U.S to study terrain-induced wind and thermodynamic conditions that influence local-scale (<5km) plume transport under varying atmospheric forcing conditions. Meteorological observations were collected using 10-m tall meteorological towers, 2-m tall tripods with 3-d sonic anemometers, a 3-m tall eddy covariance flux tower, Doppler profiling lidars, Doppler scanning lidars, weather-balloon launched radiosondes, and a tethered balloon equipped with wind, temperature, and aerosol sensors at heights up to 800 m. A smoke tracer was released along three transects in the horizontal and vertical directions and observed with video cameras, aerosol sensors and lidars (via aerosol backscatter). The observations showed evidence of large-scale/synoptic transience as well as local-scale upslope and downslope flows, along-axis valley flows, recirculation eddies on leeward slopes, and periods of strong shear and veer aloft. The release days were classified as either synoptically-driven or locally-driven, and a single case day is presented in detail for each. Synoptically-forced days show relatively narrow smoke plumes traveling down the valley from north to south (with the predominant wind direction), with little deviation in transport direction regardless of the elevation or ground locations of the smoke releases, except near the presence of leeside recirculation eddies. Locally-forced days exhibit a wider range of plume behavior due to the combination of thermally-induced valley and slope flows, which are often flowing in different cardinal directions, and wind shear found aloft at higher altitudes and elevations. We saw evidence of smoke lofting on top of the mesas due to strong upslope flows on these days. A major finding of this experiment was the effectiveness of scanning lidars to measure 2-dimensional plume transport out to a 2-3 km distance; much farther than could be visibly observed. METEX21 was the first of three planned tracer experiments at NNSS, and future experiments will incorporate multiple tracers to improve individual plume identification so that finer resolution flow details can be attained from these measurements, as well as deploy a larger suite of meteorological instrumentation, including more temperature profiling data. [ABSTRACT FROM AUTHOR]

Over heterogeneous, mountainous terrain, the determination of spatial heterogeneity of any type of a turbulent layer has been known to pose substantial challenges in mountain meteorology. In addition to the combined effect in which buoyancy and shear contribute to the turbulence intensity of such layers, it is well known that mountains add an additional degree of complexity via non-local transport mechanisms, compared to flatter topography. It is therefore the aim of this study to determine the vertical depths of both daytime convectively and shear-driven boundary layers within a fairly wide and deep Alpine Valley during summertime. Specifically, three Doppler lidars deployed during the CROSSINN (Cross-valley flow in the Inn Valley investigated by dual-Doppler lidar measurements) campaign within a single week in August 2019 are used to this end, as they were deployed along a transect nearly perpendicular to the along-valley axis. To achieve this, a bottom-up exceedance threshold method based on turbulent Doppler spectrum width sampled by the three lidars has been developed and calibrated against a more traditional bulk-Richardson number approach applied to radiosonde profiles obtained above the valley floor. The method was found to adequately capture the depths of convective turbulent boundary layers at a 1-min temporal and 50-m spatial resolution across the valley, with the degree of ambiguity increasing once surface convection decayed and upvalley flows gained in intensity over the course of the afternoon and evening hours. Analysis of four Intensive Observation Period (IOP) events elucidated three regimes of the daytime mountain boundary layer in this section of the Inn Valley. Each of the three regimes has been analyzed as a function of surface sensible heat flux $H$, upper-level valley stability $\Gamma$, and upper-level subsidence $w_L$ estimated with the coplanar retrieval method. Finally, the positioning of the three Doppler lidars in a cross-valley configuration enabled one of the most highly spatially and temporally resolved observational convective boundary layer depth data sets during daytime and over complex terrain to date. [ABSTRACT FROM AUTHOR]

A 25‐year set of daily radiosonde data was used to investigate temperature and humidity inversions at Neumayer Station, coastal Dronning Maud Land, Antarctica. For the first time, inversions were studied differentiating between different synoptic conditions and different height levels. It was shown that, generally, inversions occurred on the majority (78%) of the days, with simultaneous occurrence of humidity and temperature inversions being observed on approximately two thirds of all days. Multiple inversions are common in all seasons for cyclonic and noncyclonic conditions, however, typically occur more frequently under cyclonic conditions. The seasonality of inversion occurrence and features, that is, inversion strength, depth and vertical gradients, was analysed statistically. Different formation mechanisms depending on inversion levels and prevailing weather situations are related to typical annual courses of certain inversion features. Winter maxima were found for the features that are mostly connected to the temperature close to the surface, which is mainly a result of the negative energy balance, thus influencing surface‐based inversions. At the second level, both temperature and humidity inversions are often caused by advection of comparably warm and moist air masses related to the passage of cyclones and their frontal systems. Hence, maxima in several inversion features are found in spring and fall, when cyclonic activity is strongest. Monthly mean profiles of humidity and temperature inversions reveal that elevated inversions are often obscured in average profiles due to large variations in inversion height and depth. [ABSTRACT FROM AUTHOR]

The physical mechanisms responsible for the formation of a thermally driven cross-basin circulation in a basin with asymmetric heating of opposite mountain sidewalls are investigated. A large-eddy simulation is performed with the Weather Research and Forecasting model for an idealized basin based on the topography of Arizona's Meteor Crater. The individual components of the horizontal momentum and thermodynamic balance equations are analyzed to determine their respective contributions in forcing the cross-basin circulation. A cross-basin pressure gradient, with higher pressure on the less irradiated sidewall, leads to the development of a cross-basin flow near the basin floor. A weak opposing return flow develops above this cross-basin flow as a result of a reversed cross-basin pressure gradient. The reversed cross-basin pressure gradient is caused by cold-air advection by upslope winds in the stable morning atmosphere on the sunlit sidewall and warm-air advection by downslope winds on the still shaded sidewall, as this reverses the cross-basin temperature gradient, producing a higher temperature on the less sunlit sidewall. [ABSTRACT FROM AUTHOR]

Over flat and horizontally homogeneous terrain, vertical exchange mechanisms govern the coupling between the surface and the free troposphere. However, over sloping terrain and heterogeneous land-use, this coupling takes a three-dimensional character across a range of spatial scales, introducing uncertainties when attempting to parameterize resulting flow structures in operational numerical weather prediction. Superposition of these spatial scales is particularly pronounced in mountain valleys, for which a theoretical framework capable of explaining such alteration of exchange mechanisms does not currently exist. The resulting flow structures may assume several different properties and formations, ranging from asymmetrical cross-valley circulation cells to curvature-induced circulations accompanied with marked turbulence. To date, such flow structures have been sampled only during a few selected ambient conditions and with limited spatio-temporal resolution, leaving many open-ended questions as to their persistence and their effect on the coupling between the surface and the free troposphere. To address these questions and improve our understanding of the evolution of such cross-valley flow, we conducted the CROSSINN (Crossvalley flow in the Inn Valley investigated by dual-Doppler lidar measurements) field campaign in the Inn Valley, Austria, from 1 August to 13 October 2019. In this talk, we present preliminary findings from one Intensive Observation Period (IOP). The thermodynamic state of the mountain boundary layer during this IOP was sampled with a rich suite of measurements, including five Doppler LiDARs, a Raman LiDAR, a ceilometer, a microwave radiometer, surface energy balance measurements, as well as frequent radiosoundings. To sample the cross-valley flow structure with adequate spatio-temporal resolution, three Leosphere Doppler LiDARs Windcube 200s, which are part of the mobile integrated atmospheric observation platform KITcube, were set up in two dual-Doppler configurations covering each one half of the valley atmosphere in a single vertical plane. Such a configuration enabled the retrieval of two components of the wind field along this single vertical plane, giving us desired insight into the structure of the cross-valley flow. The spatial coverage, with the extent of 5x3 square kilometers on average, was resolved with a 50-m grid spacing throughout the entire duration of CROSSINN, sufficiently fine to assess the spatial extent of the cross-valley flow observed during this IOP. During this IOP, we observed several features of interest, including a twice daily transition from nighttime downvalley to more intense daytime upvalley flow and vice versa, as well as a shallow daytime convective boundary layer. Owing to the intense upvalley flow, the cross-valley flow structure, as obtained from the dual-Doppler algorithm, resembled an asymmetrical, single closed cell restricted to altitudes below the surrounding Alpine ridgetops. [ABSTRACT FROM AUTHOR]

Our understanding of complex biological systems is based on high-quality proteomics tools for the parallelized detection and quantification of protein interactions. Current screening platforms, however, rely on measuring protein interactions in rather artificial systems, rendering the results difficult to confer on the in vivo situation. We describe here a detailed protocol for the design and the construction of a system to detect and quantify interactions between a fluorophore-labeled protein ("prey") and a membrane protein ("bait") in living cells. Cells are plated on micropatterned surfaces functionalized with antibodies to the bait exoplasmic domain. Bait-prey interactions are assayed via the redistribution of the fluorescent prey. The method is characterized by high sensitivity down to the level of single molecules, the capability to detect weak interactions, and high throughput, making it applicable as a screening tool. The proof-of-concept is demonstrated for the interaction between CD4, a major coreceptor in T-cell signaling, and Lck, a protein tyrosine kinase essential for early T-cell signaling., (Copyright 2010 Elsevier Inc. All rights reserved.)