Detailed Dual-Doppler Structure of Kelvin–Helmholtz Waves from an Airborne Profiling Radar over Complex Terrain. Part I: Dynamic Structure

2020 ◽  
Vol 77 (5) ◽  
pp. 1761-1782 ◽  
Author(s):  
Coltin Grasmick ◽  
Bart Geerts
Keyword(s):  
Complex Terrain ◽  
Doppler Radar ◽  
Vertical Plane ◽  
Dynamic Structure ◽  
Radar Data ◽  
Range Resolution ◽  
Small Complex ◽  
Steep Terrain ◽  
Airborne Doppler Radar ◽  
The Waves

Abstract Kelvin–Helmholtz (KH) waves are remarkably common in deep stratiform precipitation systems associated with frontal disturbances, at least in the vicinity of complex terrain, as is evident from transects of vertical velocity and 2D circulation, obtained from a 3-mm airborne Doppler radar, the Wyoming Cloud Radar. The high range resolution of this radar (~40 m) allows detection and depiction of KH waves in fine detail. These waves are observed in a variety of wavelengths, depths, amplitudes, and turbulence intensities. Proximity rawinsonde data confirm that they are triggered in layers where the Richardson number is very small. Complex terrain may locally enhance wind shear, leading to KH instability. In some KH waves, the flow remains mostly laminar, while in other cases it breaks down into turbulence. KH waves are frequently locked to the terrain, and occur at various heights, including within the free troposphere, at the boundary layer top, and close to the surface. They are observed not only upwind of terrain barriers, as has been documented before, but also in the wake of steep terrain, where the waves can be highly turbulent. Vertical-plane dual-Doppler analyses of KH waves reveal the mixing of layers of differential momentum across the high-shear zone. Doppler radar data are used to explore the dynamics of KH waves, including the response of thermodynamic and kinematic variables above, below, and within the instability layer.

small-scale updrafts and snow growth in stratiform orographic clouds

2020 ◽  
Author(s):  
Bart Geerts ◽  
Coltin Grasmick ◽  
Robert Rauber
Keyword(s):  
Complex Terrain ◽  
Doppler Radar ◽  
Radar Data ◽  
Droplet Growth ◽  
Small Scale ◽  
Range Resolution ◽  
Stratiform Clouds ◽  
Orographic Clouds ◽  
Steep Terrain ◽  
Vertically Propagating

<p>Stratiform clouds over mountains are subject to locally strong updrafts that impact snow growth. These vertical drafts occur at a range of horizontal scales and depth, and include vertically propagating gravity waves, shallow terrain-driven (evanescent) waves, embedded convection, and shear-driven overturning cells. The latter essentially are Kelvin-Helmholtz (KH) waves; we find them to be remarkably common in deep stratiform precipitation systems associated with frontal disturbances over complex terrain, as is evident from transects of vertical velocity and 2D circulation, obtained from a 3-mm airborne Doppler radar. The high range resolution of this radar (~40 m) allows detection and depiction of KH waves in fine detail. These waves are observed in a variety of wavelengths (<100 m to > 1 km), depths, amplitudes, and turbulence intensities. Proximity rawinsonde data confirm that they are triggered in layers where the Richardson number is very small. Complex terrain may locally enhance wind shear, leading to KH instability.  In some KH waves, the flow remains mostly laminar, while in other cases it breaks down into turbulence. KH waves are frequently locked to the terrain, and occur at various heights, including within the free troposphere, at the boundary layer top, and close to the surface. They are observed not only upwind of terrain barriers, as has been documented before, but also in the wake of steep terrain, where the waves can be highly turbulent.  Doppler radar data and flight-level cloud probe data are used to explore the dynamics of KH waves and the response in terms of droplet growth, ice initiation, and snow growth.</p>

Finescale Vertical Structure of a Cold Front as Revealed by an Airborne Doppler Radar

2006 ◽  
Vol 134 (1) ◽  
pp. 251-271 ◽  
Author(s):  
Bart Geerts ◽  
Rick Damiani ◽  
Samuel Haimov
Keyword(s):  
Vertical Structure ◽  
Doppler Radar ◽  
Cold Front ◽  
Vertical Plane ◽  
Radar Data ◽  
Doppler Velocity ◽  
Density Current ◽  
Convective Boundary ◽  
Flight Level ◽  
Airborne Doppler Radar

Abstract In the afternoon of 24 May 2002, a well-defined and frontogenetic cold front moved through the Texas panhandle. Detailed observations from a series of platforms were collected near the triple point between this cold front and a dryline boundary. This paper primarily uses reflectivity and Doppler velocity data from an airborne 95-GHz radar, as well as flight-level thermodynamic data, to describe the vertical structure of the cold front as it intersected with the dryline. The prefrontal convective boundary layer was weakly capped, weakly sheared, and about 2.5 times deeper than the cold-frontal density current. The radar data depict the cold front as a fine example of an atmospheric density current at unprecedented detail (∼40 m). The echo structure and dual-Doppler-inferred airflow in the vertical plane reveal typical features such as a nose, a head, a rear-inflow current, and a broad current of rising prefrontal air that feeds the accelerating front-to-rear current over the head. The 2D cross-frontal structure, including the frontal slope, is highly variable in time or alongfront distance. Along this slope horizontal vorticity, averaging ∼0.05 s−1, is generated baroclinically, and the associated strong cross-front shear triggers Kelvin–Helmholtz (KH) billows at the density interface. Some KH billows occupy much of the depth of the density current, possibly even temporarily cutting off the head from its trailing body.

Mapping of Airborne Doppler Radar Data

1994 ◽  
Vol 11 (2) ◽  
pp. 572-578 ◽  
Author(s):  
Wen-Chau Lee ◽  
Peter Dodge ◽  
Frank D. Marks ◽  
Peter H. Hildebrand
Keyword(s):  
Doppler Radar ◽  
Radar Data ◽  
Doppler Radar Data ◽  
Airborne Doppler Radar

scholarly journals Procedures to Improve the Accuracy of Airborne Doppler Radar Data

2002 ◽  
Vol 19 (3) ◽  
pp. 322-339 ◽  
Author(s):  
Brian L. Bosart ◽  
Wen-Chau Lee ◽  
Roger M. Wakimoto
Keyword(s):  
Doppler Radar ◽  
Radar Data ◽  
Correction Method ◽  
Fine Tuning ◽  
Earth Surface ◽  
Doppler Radar Data ◽  
Tilt Error ◽  
Corrected Data ◽  
Flight Level ◽  
Airborne Doppler Radar

Abstract The navigation correction method proposed in Testud et al. (referred to as the THL method) systematically identifies uncertainties in the aircraft Inertial Navigation System and errors in the radar-pointing angles by analyzing the radar returns from a flat and stationary earth surface. This paper extends the THL study to address 1) error characteristics on the radar display, 2) sensitivity of the dual-Doppler analyses to navigation errors, 3) fine-tuning the navigation corrections for individual flight legs, and 4) identifying navigation corrections over a flat and nonstationary earth surface (e.g., ocean). The results show that the errors in each of the parameters affect the dual-Doppler wind analyses and the first-order derivatives in different manners. The tilt error is the most difficult parameter to determine and has the greatest impact on the dual-Doppler analysis. The extended THL method can further reduce the drift, ground speed, and tilt errors in all flight legs over land by analyzing the residual velocities of the earth surface using the corrections obtained in the calibration legs. When reliable dual-Doppler winds can be deduced at flight level, the Bosart–Lee–Wakimoto method presented here can identify all eight errors by satisfying three criteria: 1) the flight-level dual-Doppler winds near the aircraft are statistically consistent with the in situ winds, 2) the flight-level dual-Doppler winds are continuous across the flight track, and 3) the surface velocities of the left (right) fore radar have the same magnitude but opposite sign as their counterparts of right (left) aft radar. This procedure is able to correct airborne Doppler radar data over the ocean and has been evaluated using datasets collected during past experiments. Consistent calibration factors are obtained in multiple legs. The dual-Doppler analyses using the corrected data are statistically superior to those using uncorrected data.

scholarly journals The OWLeS IOP2b Lake-Effect Snowstorm: Dynamics of the Secondary Circulation

2017 ◽  
Vol 145 (7) ◽  
pp. 2437-2459 ◽  
Author(s):  
Philip T. Bergmaier ◽  
Bart Geerts ◽  
Leah S. Campbell ◽  
W. James Steenburgh
Keyword(s):  
Doppler Radar ◽  
Vertical Plane ◽  
Wrf Model ◽  
Lake Ontario ◽  
Radar Data ◽  
Secondary Circulation ◽  
Land Breeze ◽  
Lake Effect ◽  
Axis Parallel ◽  
Convergence Zones

Intense lake-effect snowfall results from a long-lake-axis-parallel (LLAP) precipitation band that often forms when the flow is parallel to the long axis of an elongated body of water, such as Lake Ontario. The intensity and persistence of the localized precipitation along the downwind shore and farther inland suggests the presence of a secondary circulation that helps organize such a band, and maintain it for some time as the circulation is advected inland. Unique airborne vertical-plane dual-Doppler radar data are used here to document this secondary circulation in a deep, well-organized LLAP band observed during intensive observing period (IOP) 2b of the Ontario Winter Lake-effect Systems (OWLeS) field campaign. The circulation, centered on a convective updraft, intensified toward the downwind shore and only gradually weakened inland. The question arises as to what sustains such a circulation in the vertical plane across the LLAP band. WRF Model simulations indicate that the primary LLAP band and other convergence zones observed over Lake Ontario during this IOP were initiated by relatively shallow airmass boundaries, resulting from a thermal contrast (i.e., land-breeze front) and differential surface roughness across the southern shoreline. Airborne radar data near the downwind shore of the lake indicate that the secondary circulation was much deeper than these shallow boundaries and was sustained primarily by rather symmetric solenoidal forcing, enhanced by latent heat release within the updraft region.

scholarly journals A Generalized Navigation Correction Method for Airborne Doppler Radar Data

2018 ◽  
Vol 35 (10) ◽  
pp. 1999-2017 ◽  
Author(s):  
Huaqing Cai ◽  
Wen-Chau Lee ◽  
Michael M. Bell ◽  
Cory A. Wolff ◽  
Xiaowen Tang ◽  
...  
Keyword(s):  
Doppler Radar ◽  
Radar Data ◽  
Correction Method ◽  
Ground Speed ◽  
Flat Surfaces ◽  
Doppler Radar Data ◽  
Flight Level ◽  
The Cost ◽  
Navigation Errors ◽  
Airborne Doppler Radar

AbstractUncertainties in aircraft inertial navigation system and radar-pointing angles can have a large impact on the accuracy of airborne dual-Doppler analyses. The Testud et al. (THL) method has been routinely applied to data collected by airborne tail Doppler radars over flat and nonmoving terrain. The navigation correction method proposed in Georgis et al. (GRH) extended the THL method over complex terrain and moving ocean surfaces by using a variational formulation but its capability over ocean has yet to be tested. Recognizing the limitations of the THL method, Bosart et al. (BLW) proposed to derive ground speed, tilt, and drift errors by statistically comparing aircraft in situ wind with dual-Doppler wind at the flight level. When combined with the THL method, the BLW method can retrieve all navigation errors accurately; however, it can be applied only to flat surfaces, and it is rather difficult to automate. This paper presents a generalized navigation correction method (GNCM) based on the GRH method that will serve as a single algorithm for airborne tail Doppler radar navigation correction for all possible surface conditions. The GNCM includes all possible corrections in the cost function and implements a new closure assumption by taking advantage of an accurate aircraft ground speed derived from GPS technology. The GNCM is tested extensively using synthetic airborne Doppler radar data with known navigation errors and published datasets from previous field campaigns. Both tests show the GNCM is able to correct the navigation errors associated with airborne tail Doppler radar data with adequate accuracy.

Quadrant Distribution of Tropical Cyclone Inner-Core Kinematics in Relation to Environmental Shear

2014 ◽  
Vol 71 (7) ◽  
pp. 2713-2732 ◽  
Author(s):  
Jennifer C. DeHart ◽  
Robert A. Houze ◽  
Robert F. Rogers
Keyword(s):  
Tropical Cyclone ◽  
Inner Core ◽  
Doppler Radar ◽  
Radar Data ◽  
Low Level ◽  
Strong Convection ◽  
Upper Level ◽  
Airborne Doppler Radar ◽  
The Vertical Distribution ◽  
Left Quadrant

Abstract Airborne Doppler radar data collected in tropical cyclones by National Oceanic and Atmospheric Administration WP-3D aircraft over an 8-yr period (2003–10) are used to statistically analyze the vertical structure of tropical cyclone eyewalls with reference to the deep-layer shear. Convective evolution within the inner core conforms to patterns shown by previous studies: convection initiates downshear right, intensifies downshear left, and weakens upshear. Analysis of the vertical distribution of radar reflectivity and vertical air motion indicates the development of upper-level downdrafts in conjunction with strong convection downshear left and a maximum in frequency upshear left. Intense updrafts and downdrafts both conform to the shear asymmetry pattern. While strong updrafts occur in the eyewall, intense downdrafts show far more radial variability, particularly in the upshear-left quadrant, though they concentrate along the eyewall edges. Strong updrafts are collocated with low-level inflow and upper-level outflow superimposed on the background flow. In contrast, strong downdrafts occur in association with low-level outflow and upper-level inflow.

scholarly journals Variational Pseudo-Multiple-Doppler Wind Retrieval in the Vertical Plane for Ground-Based Mobile Radar Data

2007 ◽  
Vol 24 (7) ◽  
pp. 1165-1185 ◽  
Author(s):  
Christopher C. Weiss ◽  
Howard B. Bluestein ◽  
Robert Conzemius ◽  
Evgeni Fedorovich
Keyword(s):  
Doppler Radar ◽  
Vertical Plane ◽  
Radar Data ◽  
Radial Component ◽  
Processing Technique ◽  
Observation System ◽  
Observation Error ◽  
Convective Boundary ◽  
Wind Retrieval ◽  
The Difference

Abstract A variational procedure is developed that utilizes mobile ground-based range–height indicator (RHI) Doppler radar velocity data for the synthesis of two-dimensional, RHI plane wind vectors. The radial component winds are obtained with the radar platform in motion, a data collection strategy referred to as the rolling RHI technique. Using the assumption of stationarity—standard to any pseudo-multiple-Doppler processing technique—individual radial velocity values at a given point in space will contribute a varying amount of independent information to the two components of wind velocity in the RHI plane, depending strongly on the difference in radar viewing angles amongst the looks. The variational technique is tested successfully with observation system simulation experiments, using both a homogeneous flow field and large eddy simulation (LES) output from a highly sheared convective boundary layer simulation. Pseudoradar data are collected in these tests in a manner consistent with the specifications of the University of Massachusetts mobile W-band radar, which was used in a separate study to resolve the finescale structure of a dryline during the International H2O Project (IHOP_2002). The results of these tests indicate clearly that the technique performs well in regions of adequate “look” angle separation. Observation error contributes significantly to the analysis when the radar looks become more collinear.

scholarly journals An Undular Bore and Gravity Waves Illustrated by Dramatic Time-Lapse Photography

2010 ◽  
Vol 27 (8) ◽  
pp. 1355-1361 ◽  
Author(s):  
Timothy A. Coleman ◽  
Kevin R. Knupp ◽  
Daryl E. Herzmann
Keyword(s):  
Gravity Waves ◽  
Doppler Radar ◽  
Time Lapse ◽  
Radar Data ◽  
Horizontal Wind ◽  
Undular Bore ◽  
Unstable Layer ◽  
Atmospheric Gravity ◽  
The Waves ◽  
Time Lapse Photography

Abstract On 6 May 2007, an intense atmospheric undular bore moved over eastern Iowa. A “Webcam” in Tama, Iowa, captured dramatic images of the effects of the bore and associated gravity waves on cloud features, because its viewing angle was almost normal to the propagation direction of the waves. The time lapse of these images has become a well-known illustration of atmospheric gravity waves. The environment was favorable for bore formation, with a wave-reflecting unstable layer above a low-level stable layer. Surface pressure and wind data are correlated for the waves in the bore, and horizontal wind oscillations are also shown by Doppler radar data. Quantitative analysis of the time-lapse photography shows that the sky brightens in wave troughs because of subsidence and darkens in wave ridges because of ascent.

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