Qun Miao

Influence of Land Cover and Soil Moisture on the Horizontal Distribution of Sensible and Latent Heat Fluxes in Southeast Kansas during IHOP_2002 and CASES-97

Abstract Analyses of daytime fair-weather aircraft and surface-flux tower data from the May–June 2002 International H2O Project (IHOP_2002) and the April–May 1997 Cooperative Atmosphere Surface Exchange Study (CASES-97) are used to document the role of vegetation, soil moisture, and terrain in determining the horizontal variability of latent heat LE and sensible heat H along a 46-km flight track in southeast Kansas. Combining the two field experiments clearly reveals the strong influence of vegetation cover, with H maxima over sparse/dormant vegetation, and H minima over green vegetation; and, to a lesser extent, LE maxima over green vegetation, and LE minima over sparse/dormant vegetation. If the small number of cases is producing the correct trend, other effects of vegetation and the impact of soil moisture emerge through examining the slope ΔxyLE/ΔxyH for the best-fit straight line for plots of time-averaged LE as a function of time-averaged H over the area. Based on the surface energy balance, H + LE ...

The Use of Millimeter Doppler Radar Echoes to Estimate Vertical Air Velocities in the Fair-Weather Convective Boundary Layer

Abstract Vertical velocity characteristics of the optically clear convective boundary layer (CBL) are examined by means of profiling airborne radar data collected in the central Great Plains during the International H2O Project, May–June 2002 (IHOP 2002). Clear-air echoes are sufficiently strong for the radar, a 95-GHz cloud radar, to detect most of the CBL at a resolution of ∼30 m. Vertical radar transects across the CBL are remarkably dominated by well-defined plumes of higher reflectivity. These echo plumes occupy most of the depth of the CBL in the developing and mature stages of the CBL. Gust probe data indicate that the plumes tend to correspond with ascending motion. Evidence exists in the literature, and arises from this study, that the clear-air scatterers are mostly small insects. The close-range Doppler radar velocities, some 100 m above and below the aircraft, are compared to gust probe vertical velocities after both are corrected for aircraft motion. It is found that the radar vertical veloci...

Simulating the IHOP_2002 Fair-Weather CBL with the WRF-ARW–Noah Modeling System. Part II: Structures from a Few Kilometers to 100 km across

Abstract Fair-weather data along the May–June 2002 International H2O Project (IHOP_2002) eastern track and the nearby Argonne Boundary Layer Experiments (ABLE) facility in southeast Kansas are compared to numerical simulations to gain insight into how the surface influences convective boundary layer (CBL) structure, and to evaluate the success of the modeling system in replicating the observed behavior. Simulations are conducted for 4 days, using the Advanced Research version of the Weather Research and Forecasting (WRF) model coupled to the Noah land surface model (LSM), initialized using the High-Resolution Land Data Assimilation System (HRLDAS). Because the observations focus on phenomena less than 60 km in scale, the model is run with 1-km grid spacing, offering a critical look at high-resolution model behavior in an environment uncomplicated by precipitation. The model replicates the type of CBL structure on scales from a few kilometers to ∼100 km, but some features at the kilometer scales depend on ...

Boundary Layer Turbulence and Orographic Precipitation Growth in Cold Clouds: Evidence from Profiling Airborne Radar Data

AbstractAirborne vertically pointing Doppler radar data collected in 10 winter storms over the Medicine Bow Range in Wyoming are used to examine the importance of boundary layer (BL) turbulence for orographic precipitation growth. In all 10 cases, the cloud-base temperature was below 0°C and the bulk Froude number was more than 1.0, implying little or no blocking of the flow by the mountain barrier. Seven of the 10 storms sampled were postfrontal, with weak static stability and relatively shallow cloud tops.Doppler vertical velocity transects depict an approximately 1-km-deep turbulent layer draped over the terrain, sometimes clearly distinct from the stratified flow in the free troposphere aloft, where vertical motion is largely controlled by gravity wave dynamics. Spectral analysis of near-surface Doppler vertical velocity data in terrain-following coordinates reveals an inertial subrange with decreasing power with height toward the BL top. The composite of radar data profiles from the 10 flights is ana...

An Airborne Profiling Radar Study of the Impact of Glaciogenic Cloud Seeding on Snowfall from Winter Orographic Clouds

Abstract Data from an airborne vertically pointing millimeter-wave Doppler radar are used to study the cloud microphysical effect of glaciogenic seeding of cold-season orographic clouds. Fixed flight tracks were flown downstream of ground-based silver iodide (AgI) generators in the Medicine Bow Mountains of Wyoming. Composite data from seven flights, each with a no-seeding period followed by a seeding period, indicate that radar reflectivity was higher near the ground during the seeding periods. Several physical considerations argue in favor of the hypothesis that the increase in near-surface reflectivity is attributed to AgI seeding. While the increase in near-surface reflectivity and thus snowfall rate are statistically significant, caution is warranted in view of the large natural variability of weather conditions and the small size of the dataset.

Simulating the IHOP_2002 Fair-Weather CBL with the WRF-ARW-Noah Modeling System. Part I: Surface Fluxes and CBL Structure and Evolution along the Eastern Track

Abstract Fair-weather data from the May–June 2002 International H2O Project (IHOP_2002) 46-km eastern flight track in southeast Kansas are compared to simulations using the advanced research version of the Weather Research and Forecasting model coupled to the Noah land surface model (LSM), to gain insight into how the surface influences convective boundary layer (CBL) fluxes and structure, and to evaluate the success of the modeling system in representing CBL structure and evolution. This offers a unique look at the capability of the model on scales the length of the flight track (46 km) and smaller under relatively uncomplicated meteorological conditions. It is found that the modeled sensible heat flux H is significantly larger than observed, while the latent heat flux (LE) is much closer to observations. The slope of the best-fit line ΔLE/ΔH to a plot of LE as a function of H, an indicator of horizontal variation in available energy H + LE, for the data along the flight track, was shallower than observe...

Airborne radar observations of the flight behavior of small insects in the atmospheric convective boundary layer

Abstract The vertical flight behavior of insects in the convective boundary layer (CBL) is examined by means of profiling airborne Doppler radar data collected in the central Great Plains in late spring. On fair-weather days, the CBL grows from the ground up in morning hours and matures at a depth of 1,000–1,500 m shortly after midday. It is well mixed by thermals bubbling up from near the surface. Nevertheless the CBL is dominated, over its entire depth, by well-defined regions of high insect concentrations, here referred to as insect plumes. This is inferred from radar, whose echoes in the CBL are largely caused by microinsects (<10 mm diameter). This study focuses on the vertical motion of the radar scatterers relative to the vertical air motion, in natural conditions. It is shown that insect plumes tend to be collocated with updrafts in the CBL and that microinsects tend to fall or fly down against the updrafts at an average speed of 0.5 ± 0.2 m/s. This estimate is based on a comparison of the close-range radar velocities, some 100 m above and below the aircraft, with the vertical air velocity measured at flight level. We hypothesize that the gregarious behavior of small insects in the CBL is explained by their tendency to oppose updrafts at a rate that is surprisingly proportional to the updraft strength. This finding is also strong evidence for the biotic nature of the echo plumes. This hypothesis is tested elsewhere by means of a simple numerical simulation.

Pressure Perturbations and Upslope Flow over a Heated, Isolated Mountain

Abstract Surface and upper-air data, collected as part of the Cumulus Photogrammetric, In Situ, and Doppler Observations (CuPIDO) experiment during the 2006 monsoon season around the Santa Catalina Mountains in southeast Arizona, are used to study the diurnal variation of the mountain-scale surface convergence and its thermal forcing. The thermal forcing is examined in terms of a horizontal pressure gradient force, which is derived assuming hydrostatic balance. The mountain is ∼30 km in diameter, ∼2 km high, and relatively isolated. The environment is characterized by weak winds, a deep convective boundary layer in the afternoon, and sufficient low-level moisture for orographic cumulus convection on most days. The katabatic, divergent surface flow at night and anabatic, convergent flow during the day are in phase with the diurnal variation of the horizontal pressure gradient force, which points toward the mountain during the day and away from the mountain at night. The daytime pressure deficit over the mo...

Finescale Vertical Structure and Dynamics of Some Dryline Boundaries Observed in IHOP

Abstract Several radar fine lines, all with a humidity contrast, were sampled in the central Great Plains during the 2002 International H2O Project (IHOP). This study primarily uses aircraft and airborne millimeter-wave radar observations to dynamically interpret the presence and vertical structure of these fine lines as they formed within the well-developed convective boundary layer. In all cases the fine line represents a boundary layer convergence zone. This convergence sustains a sharp contrast in humidity, and usually in potential temperature, across the fine line. The key question addressed herein is whether, at the scale examined here (∼10 km), the airmass contrast itself, in particular the horizontal density (virtual potential temperature) difference and resulting solenoidal circulation, is responsible for the sustained convergence and the radar fine line. For the 10 cases examined herein, the answer is affirmative.

Vertical velocity and buoyancy characteristics of coherent echo plumes in the convective boundary layer detected by a profiling airborne lidar

Aircraft and airborne millimeter-wave radar observations are used to interpret the dynamics of radar echoes and radar-inferred updrafts within the well-developed, weakly sheared continental convective boundary layer. Vertically pointing radar reflectivity and Doppler velocity data collected above and below the aircraft, flying along fixed tracks in the central Great Plains during the International H 2 O Project (IHOP_2002), are used to define echo plumes and updraft plumes, respectively. Updraft plumes are generally narrower than echo plumes, but both types of plumes have the dynamical properties of buoyant eddies, especially at low levels. This buoyancy is driven both by temperature excess and water vapor excess over the ambient air. Plumes that are better defined in terms of reflectivity or updraft strength tend to be more buoyant.Abstract Aircraft and airborne millimeter-wave radar observations are used to interpret the dynamics of radar echoes and radar-inferred updrafts within the well-developed, weakly sheared continental convective boundary layer. Vertically pointing radar reflectivity and Doppler velocity data collected above and below the aircraft, flying along fixed tracks in the central Great Plains during the International H2O Project (IHOP_2002), are used to define echo plumes and updraft plumes, respectively. Updraft plumes are generally narrower than echo plumes, but both types of plumes have the dynamical properties of buoyant eddies, especially at low levels. This buoyancy is driven both by temperature excess and water vapor excess over the ambient air. Plumes that are better defined in terms of reflectivity or updraft strength tend to be more buoyant.