scholarly journals Observation of a Severe Wind Case Caused by Gust Front and Its Boundary Layer Structures Characteristics

2018 ◽  
Vol 53 ◽  
pp. 03010
Author(s):  
Changyi Xu ◽  
Yan Wang
Keyword(s):  
Boundary Layer ◽  
Doppler Radar ◽  
Main Body ◽  
Observation Data ◽  
High Wind ◽  
Layer Structures ◽  
Wind Profiler Radar ◽  
Outflow Boundary ◽  
Wind Intensity ◽  
Gust Front

Based on Doppler radar 3D-composited reflectivity, wind profiler radar, boundary layer Tianjin tower of 255m as well as intensified automatic surface observation data, the evolution of the boundary layer associated with two successive gust front processes in the evening of 10 June 2016 and the intensity of the related disastrous surface high wind were analyzed. The results shown as follows: (1) To the same storm cell, the wind intensity caused by the outflow boundary in the main body was stronger than the wind caused by the gust front. The intensity of the disastrous high wind was related to the maximum descending velocity in the boundary layer and the associated height. The stronger the maximum descending velocity and the lower the level, the stronger the disastrous high wind was. (2) The tower data indicated, as the approaching of the gust front, convergence fluctuations first emerged at low(20m) and middle(120m) levels of the tower, leading the emergence of disastrous high wind by 8 minutes. When the gust front passed over, the maximum variations of cooling and the wind velocity were in pace with each other.

scholarly journals Life Cycle of a Mesoscale Circular Gust Front Observed by a C-Band Doppler Radar in West Africa

2011 ◽  
Vol 139 (5) ◽  
pp. 1370-1388 ◽  
Author(s):  
Marie Lothon ◽  
Bernard Campistron ◽  
Michel Chong ◽  
Fleur Couvreux ◽  
Françoise Guichard ◽  
...  
Keyword(s):  
Boundary Layer ◽  
Life Cycle ◽  
Doppler Radar ◽  
Deep Convection ◽  
Convective System ◽  
Massachusetts Institute Of Technology ◽  
Shallow Convection ◽  
Multidisciplinary Analysis ◽  
Institute Of Technology ◽  
Gust Front

On 10 July 2006, during the Special Observation Period (SOP) of the African Monsoon Multidisciplinary Analysis (AMMA) campaign, a small convective system initiated over Niamey and propagated westward in the vicinity of several instruments activated in the area, including the Massachusetts Institute of Technology (MIT) C-band Doppler radar and the Atmospheric Radiation Measurement (ARM) mobile facility. The system started after a typical convective development of the planetary boundary layer. It grew and propagated within the scope of the radar range, so that its entire life cycle is documented, from the precluding shallow convection to its traveling gust front. The analysis of the observations during the transitions from organized dry convection to shallow convection and from shallow convection to deep convection lends support to the significant role played by surface temperature heterogeneities and boundary layer processes in the initiation of deep convection in semiarid conditions. The analysis of the system later in the day, of its growth and propagation, and of its associated density current allows the authors to estimate the wake available potential energy and demonstrate its capability to trigger deep convection itself. Given the quality and density of observations related to this case, and its typical and quasi-textbook characteristics, this is considered a prime case for the study of initiation and evolution of deep convection, and for testing their parameterizations in single-column models.

scholarly journals An Observational Study of Convection Initiation on 12 June 2002 during IHOP_2002

2008 ◽  
Vol 136 (7) ◽  
pp. 2283-2304 ◽  
Author(s):  
Tammy M. Weckwerth ◽  
Hanne V. Murphey ◽  
Cyrille Flamant ◽  
Janine Goldstein ◽  
Crystalyne R. Pettet
Keyword(s):  
Boundary Layer ◽  
Water Vapor ◽  
Gravity Waves ◽  
Doppler Radar ◽  
Internal Gravity Waves ◽  
Moist Convection ◽  
Outflow Boundary ◽  
Convection Initiation ◽  
Convective Rolls

Abstract The International H2O Project (IHOP_2002) was designed to sample the three-dimensional time-varying moisture field to better understand convective processes. Numerous research and operational water vapor measuring systems and retrievals, via in situ and remote sensing techniques, were operated in the U.S. Southern Great Plains from 13 May to 25 June 2002. This was done in combination with more traditional observations of wind and temperature. Convection initiation (CI) sampling strategies were designed to optimally employ the array of ground-based and airborne sensors to observe the processes leading to the development of deep, moist convection. This case study examines several clear-air features and their impact on CI on 12 June 2002. The supercells that developed produced damaging winds and hail. The clear-air, preconvective features included (i) a mesoscale low pressure region, (ii) a dryline, (iii) an old outflow boundary, (iv) the intersection of (ii) and (iii), (v) internal gravity waves, and (vi) horizontal convective rolls. A unique combination of instruments was positioned to sample the preconvective environment on 12 June 2002. The Lidar pour l’Etude des Interactions Aérosols Nuages Dynamique Rayonnement et du Cycle de l’Eau (LEANDRE II) water vapor differential absorption lidar (DIAL), the airborne Electra Doppler Radar (ELDORA), and the Navy Research Laboratory (NRL) P3 aircraft in situ measurements provided information on the moisture and vertical velocity distribution within the boundary layer. Radiosondes, dropsondes, wind profilers, and an Atmospheric Emitted Radiance Interferometer (AERI) provided temperature, moisture, and wind profiling information. Although other ground-based sensors (i.e., S-band dual-polarization Doppler radar, Mobile Integrated Profiling System) were 50–150 km west of the CI area, they were useful for illustrating the boundary layer kinematics and reflectivity fields. Results suggest that the mesolow and mesoscale boundaries, respectively, acted to enhance the low-level moisture advection and convergence in the CI region. While internal gravity waves were present and appeared to modulate water vapor along the old outflow boundary, they did not play an obvious role in CI in this case. Horizontal convective rolls were observed beneath the new storms that initiated and may have helped to focus the CI in this case.

Observational Analysis of a Gust Front to Bore to Solitary Wave Transition within an Evolving Nocturnal Boundary Layer

2006 ◽  
Vol 63 (8) ◽  
pp. 2016-2035 ◽  
Author(s):  
Kevin Knupp
Keyword(s):  
Boundary Layer ◽  
Solitary Wave ◽  
Doppler Radar ◽  
Mesoscale Convective System ◽  
Liquid Water Content ◽  
Nocturnal Boundary Layer ◽  
Cloud Base ◽  
Convective System ◽  
Convective Initiation ◽  
Gust Front

Abstract The evolution of a gust front to bore to solitary wave transition, and comprehensive information on the evolving nocturnal boundary layer (NBL) associated with this change, are described with analysis of radar and profiler measurements. The observations were obtained on 21 June 2002 in the Oklahoma panhandle during the International H2O Project. The evolution of this system, from a strong bore (initiated by a vigorous gust front) to a solitary wave, was observed over a 4-h period with Doppler radar and surface measurements. Detailed information on the mature bore structure was obtained by a cluster of profiling instruments including two boundary layer wind profilers, a lidar ceilometer, and a microwave profiling radiometer. A strong bore was initiated by an extensive gust front that perturbed an incipient NBL whose development (prior to sunset) was enhanced by shading from the parent mesoscale convective system. At the time of bore formation, the NBL was about 300 m deep and exhibited a surface temperature about 4 K less than the afternoon maximum. Initially, the bore assumed kinematic properties similar to those of a gust front. As the NBL stabilized, the bore matured and exhibited undular formations over 30–60-km segments along the bore axis. A 30-km-wide cloud field accompanied the mature bore system within three hours of its formation. System-relative airflow within the cloud field was front-to-rear and exhibited a primary hydraulic jump updraft (4–5 m s−1 magnitude) within the bore core. The bore core exhibited a low, smooth cloud base, a cloud depth of 2.5 km, nearly adiabatic liquid water content, and pronounced turbulence. The maximum parcel displacements within the bore were about 2 km (sufficient for marginal convective initiation), and the net parcel displacement from before to after bore passage was 0.6–0.9 km.

The Multiple-Vortex Structure of the El Reno, Oklahoma, Tornado on 31 May 2013

2018 ◽  
Vol 146 (8) ◽  
pp. 2483-2502 ◽  
Author(s):  
Howard B. Bluestein ◽  
Kyle J. Thiem ◽  
Jeffrey C. Snyder ◽  
Jana B. Houser
Keyword(s):  
Doppler Radar ◽  
Radar Data ◽  
Rapid Scan ◽  
X Band ◽  
Close Range ◽  
Formation And Evolution ◽  
Using Data ◽  
Secondary Vortices ◽  
The Right ◽  
Gust Front

Abstract This study documents the formation and evolution of secondary vortices associated within a large, violent tornado in Oklahoma based on data from a close-range, mobile, polarimetric, rapid-scan, X-band Doppler radar. Secondary vortices were tracked relative to the parent circulation using data collected every 2 s. It was found that most long-lived vortices (those that could be tracked for ≥15 s) formed within the radius of maximum wind (RMW), mainly in the left-rear quadrant (with respect to parent tornado motion), passing around the center of the parent tornado and dissipating closer to the center in the right-forward and left-forward quadrants. Some secondary vortices persisted for at least 1 min. When a Burgers–Rott vortex is fit to the Doppler radar data, and the vortex is assumed to be axisymmetric, the secondary vortices propagated slowly against the mean azimuthal flow; if the vortex is not assumed to be axisymmetric as a result of a strong rear-flank gust front on one side of it, then the secondary vortices moved along approximately with the wind.

scholarly journals On the boundary layer arising in the spin-up of a stratified fluid in a container with sloping walls

1997 ◽  
Vol 335 ◽  
pp. 233-259 ◽  
Author(s):  
P. W. DUCK ◽  
M. R. FOSTER ◽  
R. E. HEWITT
Keyword(s):  
Boundary Layer ◽  
Layer Structure ◽  
Outer Region ◽  
Stratified Fluid ◽  
Main Body ◽  
Similarity Type ◽  
Cone Apex ◽  
Uniform Solution ◽  
Steady Solutions ◽  
Finite Time Singularity

In this paper we consider the boundary layer that forms on the sloping walls of a rotating container (notably a conical container), filled with a stratified fluid, when flow conditions are changed abruptly from some initial (uniform) state. The structure of the solution valid away from the cone apex is derived, and it is shown that a similarity-type solution is appropriate. This system, which is inherently nonlinear in nature, is solved numerically for several flow regimes, and the results reveal a number of interesting and diverse features.In one case, a steady state is attained at large times inside the boundary layer. In a second case, a finite-time singularity occurs, which is fully analysed. A third scenario involves a double boundary-layer structure developing at large times, most significantly including an outer region that grows in thickness as the square-root of time.We also consider directly the nonlinear fully steady solutions to the problem, and map out in parameter space the likely ultimate flow behaviour. Intriguingly, we find cases where, when the rotation rate of the container is equal to that of the main body of the fluid, an alternative nonlinear state is preferred, rather than the trivial (uniform) solution.Finally, utilizing Laplace transforms, we re-investigate the linear initial-value problem for small differential spin-up studied by MacCready & Rhines (1991), recovering the growing-layer solution they found. However, in contrast to earlier work, we find a critical value of the buoyancy parameter beyond which the solution grows exponentially in time, consistent with our nonlinear results.

scholarly journals Evaluation of the AMPS Boundary Layer Simulations on the Ross Ice Shelf, Antarctica, with Unmanned Aircraft Observations

2017 ◽  
Vol 56 (8) ◽  
pp. 2239-2258 ◽  
Author(s):  
Jonathan D. Wille ◽  
David H. Bromwich ◽  
John J. Cassano ◽  
Melissa A. Nigro ◽  
Marian E. Mateling ◽  
...  
Keyword(s):  
Boundary Layer ◽  
Wind Speed ◽  
Relative Humidity ◽  
High Wind ◽  
Ice Shelf ◽  
High Wind Speed ◽  
Near Surface ◽  
Ross Ice Shelf ◽  
Low Cloud ◽  
The Antarctic

AbstractAccurately predicting moisture and stability in the Antarctic planetary boundary layer (PBL) is essential for low-cloud forecasts, especially when Antarctic forecasters often use relative humidity as a proxy for cloud cover. These forecasters typically rely on the Antarctic Mesoscale Prediction System (AMPS) Polar Weather Research and Forecasting (Polar WRF) Model for high-resolution forecasts. To complement the PBL observations from the 30-m Alexander Tall Tower! (ATT) on the Ross Ice Shelf as discussed in a recent paper by Wille and coworkers, a field campaign was conducted at the ATT site from 13 to 26 January 2014 using Small Unmanned Meteorological Observer (SUMO) aerial systems to collect PBL data. The 3-km-resolution AMPS forecast output is combined with the global European Centre for Medium-Range Weather Forecasts interim reanalysis (ERAI), SUMO flights, and ATT data to describe atmospheric conditions on the Ross Ice Shelf. The SUMO comparison showed that AMPS had an average 2–3 m s−1 high wind speed bias from the near surface to 600 m, which led to excessive mechanical mixing and reduced stability in the PBL. As discussed in previous Polar WRF studies, the Mellor–Yamada–Janjić PBL scheme is likely responsible for the high wind speed bias. The SUMO comparison also showed a near-surface 10–15-percentage-point dry relative humidity bias in AMPS that increased to a 25–30-percentage-point deficit from 200 to 400 m above the surface. A large dry bias at these critical heights for aircraft operations implies poor AMPS low-cloud forecasts. The ERAI showed that the katabatic flow from the Transantarctic Mountains is unrealistically dry in AMPS.

Doppler Profiler and Radar Observations of Boundary Layer Variability during the Landfall of Tropical Storm Gabrielle

2006 ◽  
Vol 63 (1) ◽  
pp. 234-251 ◽  
Author(s):  
Kevin R. Knupp ◽  
Justin Walters ◽  
Michael Biggerstaff
Keyword(s):  
Boundary Layer ◽  
Doppler Radar ◽  
Layer Structure ◽  
Flow Direction ◽  
Surface Flow ◽  
Tropical Storm ◽  
Mean Flow ◽  
Boundary Layer Structure ◽  
Stratiform Precipitation ◽  
Wind Profiles

Abstract Detailed observations of boundary layer structure were acquired on 14 September 2001, prior to and during the landfall of Tropical Storm Gabrielle. The Mobile Integrated Profiling System (MIPS) and the Shared Mobile Atmospheric Research and Teaching Radar (SMART-R) were collocated at the western Florida coastline near Venice, very close to the wind center at landfall. Prior to landfall, the boundary layer was rendered weakly stable by a long period of evaporational cooling and mesoscale downdrafts within extensive stratiform precipitation that started 18 h before landfall. The cool air mass was expansive, with an area within the 23°C surface isotherm of about 50 000 km2. East-northeasterly surface flow transported this cool air off the west coast of Florida, toward the convergent warm core of the Gabrielle, and promoted the development of shallow warm and cold fronts that were prominent during the landfall phase. Airflow properties of the boundary layer around the coastal zone are examined using the MIPS and SMART-R data. Wind profiles exhibited considerable temporal variability throughout the period of observations. The stable offshore flow within stratiform precipitation exhibited a modest jet that descended from about 600 to 300 m within the 20-km zone centered on the coastline. In contrast, the onshore flow on the western side of the wind center produced a more turbulent boundary layer that exhibited a well-defined top varying between 400 and 1000 m MSL. The horizontal variability of each boundary layer is examined using high-resolution Doppler radar scans at locations up to 15 km on either side of the coastline, along the mean flow direction of the boundary layer. These analyses reveal that transitions in boundary layer structure for both the stable and unstable regimes were most substantial within 5 km of the coastline.

scholarly journals Effective Buoyancy, Inertial Pressure, and the Mechanical Generation of Boundary Layer Mass Flux by Cold Pools

2015 ◽  
Vol 72 (8) ◽  
pp. 3199-3213 ◽  
Author(s):  
Nadir Jeevanjee ◽  
David M. Romps
Keyword(s):  
Boundary Layer ◽  
Mass Flux ◽  
Dominant Role ◽  
Deep Convection ◽  
Force Balance ◽  
Vertical Force ◽  
Inertial Forces ◽  
Buoyancy Forcing ◽  
Cold Pools ◽  
Gust Front

Abstract The Davies-Jones formulation of effective buoyancy is used to define inertial and buoyant components of vertical force and to develop an intuition for these components by considering simple cases. This decomposition is applied to the triggering of new boundary layer mass flux by cold pools in a cloud-resolving simulation of radiative–convective equilibrium (RCE). The triggering is found to be dominated by inertial forces, and this is explained by estimating the ratio of the inertial forcing to the buoyancy forcing, which scales as H/h, where H is the characteristic height of the initial downdraft and h is the characteristic height of the mature cold pool’s gust front. In a simulation of the transition from shallow to deep convection, the buoyancy forcing plays a dominant role in triggering mass flux in the shallow regime, but the force balance tips in favor of inertial forcing just as precipitation sets in, consistent with the RCE results.

scholarly journals Lower Atmospheric Wind Dynamics as Measured by the 1290 MHz Wind Profiler Radar Located at Cardington (Lat. 52.10ºN, Long. 0.42ºE), UK and Their Comparisons with Near-by Radiosonde Instrument

2020 ◽  
pp. 22-35
Author(s):  
M. Satyavani ◽  
P. S. Brahmanandam ◽  
P. S. V. Subba Rao ◽  
M. P. Rao
Keyword(s):  
Remote Sensing ◽  
Boundary Layer ◽  
Wind Speed ◽  
Universal Time ◽  
Diurnal Variations ◽  
Wind Profiler ◽  
Independent Observations ◽  
Wind Profiler Radar

This study reports diurnal variations of wind directions, wind speed of vector winds, and the evolution of boundary layer (BL) over a mid-latitude measured using a transportable 1290 MHz wind profiling radar located at Cardington (Lat. 52.10ºN; Long. 0.42ºE), Bedfordshire, UK from 17 to 28 April 2010. The horizontal winds show benign behavior during nighttime hours, while winds during daytime hours had magnitudes around, on average, 10-20 m/s, in the majority of the cases. The heights of the boundary layer (BL) varied from as low as ~1100 m to ~2600 km and BL height had shown to have evolved from 0700 universal time (UT) onwards and collapsed by 0000 UT.  Besides, a comparison made between winds measured by the 1290 MHz radar and near-by radiosonde showed a moderate similitude between them, albeit a few discrepancies are found in wind directions and speeds. The possible reasons for these discrepancies could be different volume sensing of observations of these independent observations. An attempt is, therefore, made to calculate radiosonde balloon drifts [1] for the ascending node of the balloons, which had confirmed that the balloons often drifted horizontally as long as up to 100 km. The large drifts, most probably, are the possible reasons for the mismatching of winds measured by these two independent remote sensing instruments.

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