scholarly journals Vertical Velocity and Buoyancy Characteristics of Coherent Echo Plumes in the Convective Boundary Layer, Detected by a Profiling Airborne Radar

2006 ◽  
Vol 45 (6) ◽  
pp. 838-855 ◽  
Author(s):  
Qun Miao ◽  
Bart Geerts ◽  
Margaret LeMone
Keyword(s):  
Boundary Layer ◽  
Great Plains ◽  
Convective Boundary Layer ◽  
Ambient Air ◽  
Doppler Velocity ◽  
Convective Boundary ◽  
Millimeter Wave Radar ◽  
Radar Echoes ◽  
Temperature Excess ◽  
Wave Radar

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.

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

2007 ◽  
Vol 135 (12) ◽  
pp. 4161-4184 ◽  
Author(s):  
Qun Miao ◽  
Bart Geerts
Keyword(s):  
Boundary Layer ◽  
Great Plains ◽  
Vertical Structure ◽  
Potential Temperature ◽  
Convective Boundary ◽  
Fine Line ◽  
Millimeter Wave Radar ◽  
Structure And Dynamics ◽  
Wave Radar ◽  
Virtual Potential Temperature

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.

scholarly journals A Method for Estimating the Turbulent Kinetic Energy Dissipation Rate from a Vertically Pointing Doppler Lidar, and Independent Evaluation from Balloon-Borne In Situ Measurements

2010 ◽  
Vol 27 (10) ◽  
pp. 1652-1664 ◽  
Author(s):  
Ewan J. O’Connor ◽  
Anthony J. Illingworth ◽  
Ian M. Brooks ◽  
Christopher D. Westbrook ◽  
Robin J. Hogan ◽  
...  
Keyword(s):  
Boundary Layer ◽  
Convective Boundary Layer ◽  
Sonic Anemometer ◽  
Horizontal Wind ◽  
Inertial Subrange ◽  
Doppler Velocity ◽  
Doppler Lidar ◽  
Convective Boundary ◽  
Dissipation Rates

Abstract A method of estimating dissipation rates from a vertically pointing Doppler lidar with high temporal and spatial resolution has been evaluated by comparison with independent measurements derived from a balloon-borne sonic anemometer. This method utilizes the variance of the mean Doppler velocity from a number of sequential samples and requires an estimate of the horizontal wind speed. The noise contribution to the variance can be estimated from the observed signal-to-noise ratio and removed where appropriate. The relative size of the noise variance to the observed variance provides a measure of the confidence in the retrieval. Comparison with in situ dissipation rates derived from the balloon-borne sonic anemometer reveal that this particular Doppler lidar is capable of retrieving dissipation rates over a range of at least three orders of magnitude. This method is most suitable for retrieval of dissipation rates within the convective well-mixed boundary layer where the scales of motion that the Doppler lidar probes remain well within the inertial subrange. Caution must be applied when estimating dissipation rates in more quiescent conditions. For the particular Doppler lidar described here, the selection of suitably short integration times will permit this method to be applicable in such situations but at the expense of accuracy in the Doppler velocity estimates. The two case studies presented here suggest that, with profiles every 4 s, reliable estimates of ε can be derived to within at least an order of magnitude throughout almost all of the lowest 2 km and, in the convective boundary layer, to within 50%. Increasing the integration time for individual profiles to 30 s can improve the accuracy substantially but potentially confines retrievals to within the convective boundary layer. Therefore, optimization of certain instrument parameters may be required for specific implementations.

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

2005 ◽  
Vol 22 (3) ◽  
pp. 225-246 ◽  
Author(s):  
Bart Geerts ◽  
Qun Miao
Keyword(s):  
Boundary Layer ◽  
Great Plains ◽  
Convective Boundary Layer ◽  
Doppler Radar ◽  
Vertical Displacement ◽  
Radar Data ◽  
Terminal Velocity ◽  
Convective Boundary ◽  
Biotic Response ◽  
The Difference

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 velocities have a downward bias of 0.5 ± 0.2 m s−1 on average. This bias is of the same sign as that reported in wind profiler data in the CBL, but it is larger. The difference between aircraft and radar vertical velocities becomes larger in stronger updrafts. This does not happen in cases where the scatterers are hydrometeors: hydrometeors fall out at their terminal velocity, which does not directly depend on updraft speed. The existence of the CBL echo plumes and radar “fine lines,” sustained by low-level air convergence, has long been attributed to a biotic response to updrafts. This response has been assumed to be controlled by air temperature; that is, insects subside when they encounter cold air in the upper CBL. The authors propose that the biotic response is not temperature controlled but, rather, is dependent on the vertical displacement.

scholarly journals Long-Term Observations of the Convective Boundary Layer Using Insect Radar Returns at the SGP ARM Climate Research Facility

2010 ◽  
Vol 23 (21) ◽  
pp. 5699-5714 ◽  
Author(s):  
Arunchandra S. Chandra ◽  
Pavlos Kollias ◽  
Scott E. Giangrande ◽  
Stephen A. Klein
Keyword(s):  
Boundary Layer ◽  
Vertical Velocity ◽  
Convective Boundary Layer ◽  
Turbulent Transport ◽  
Doppler Velocity ◽  
Research Facility ◽  
Convective Boundary ◽  
Climate Research ◽  
Turbulent Statistics

Abstract A long-term study of the turbulent structure of the convective boundary layer (CBL) at the U.S. Department of Energy Atmospheric Radiation Measurement Program (ARM) Southern Great Plains (SGP) Climate Research Facility is presented. Doppler velocity measurements from insects occupying the lowest 2 km of the boundary layer during summer months are used to map the vertical velocity component in the CBL. The observations cover four summer periods (2004–08) and are classified into cloudy and clear boundary layer conditions. Profiles of vertical velocity variance, skewness, and mass flux are estimated to study the daytime evolution of the convective boundary layer during these conditions. A conditional sampling method is applied to the original Doppler velocity dataset to extract coherent vertical velocity structures and to examine plume dimension and contribution to the turbulent transport. Overall, the derived turbulent statistics are consistent with previous aircraft and lidar observations. The observations provide unique insight into the daytime evolution of the convective boundary layer and the role of increased cloudiness in the turbulent budget of the subcloud layer. Coherent structures (plumes–thermals) are found to be responsible for more than 80% of the total turbulent transport resolved by the cloud radar system. The extended dataset is suitable for evaluating boundary layer parameterizations and testing large-eddy simulations (LESs) for a variety of surface and cloud conditions.

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