scholarly journals Numerical Models of Boundary Layer Processes over and around the Gulf of Mexico during a Return-Flow Event

1998 ◽  
Vol 13 (4) ◽  
pp. 921-933 ◽  
Author(s):  
A. Birol Kara ◽  
James B. Elsner ◽  
Paul H. Ruscher
Keyword(s):  
Boundary Layer ◽  
Gulf Of Mexico ◽  
Numerical Models ◽  
Return Flow ◽  
Boundary Layer Processes

scholarly journals Resolution Dependence of Initiation and Upscale Growth of Deep Convection in Convection-Allowing Forecasts of the 31 May–1 June 2013 Supercell and MCS

2015 ◽  
Vol 143 (11) ◽  
pp. 4331-4354 ◽  
Author(s):  
Russ S. Schumacher
Keyword(s):  
Boundary Layer ◽  
Numerical Models ◽  
Deep Convection ◽  
Squall Line ◽  
Cold Pool ◽  
Model Resolution ◽  
Grid Spacing ◽  
Boundary Layer Processes ◽  
High Impact Weather ◽  
Supercell Thunderstorm

Abstract On 31 May 2013, a supercell thunderstorm initiated in west-central Oklahoma and produced a deadly tornado. This convection then grew upscale, with a nearly stationary line developing early on 1 June that produced very heavy rainfall and caused deadly flash flooding in the Oklahoma City area. Real-time convection-allowing (Δx = 4 km) model forecasts used during the Mesoscale Predictability Experiment (MPEX) provided accurate guidance regarding the timing, location, and evolution of convection in this case. However, attempts to simulate this event at higher resolution degraded the forecast, with the primary supercell failing to initiate and the evolution of the overnight MCS not resembling the observed system. Experiments to test the dependence of forecasts of this event on model resolution show that with grid spacing smaller than 4 km, mixing along the dryline in northwest Texas was more vigorous, causing low-level dry air to move more quickly eastward into Oklahoma. This drying prevented the supercell from initiating near the triple point in the higher-resolution simulations. Then, the lack of supercellular convection and its associated cold pool altered the evolution of subsequent convection. Whereas in observations and the 4-km forecast, a nearly stationary MCS developed parallel to, but displaced from, the supercell’s cold pool, the higher-resolution simulations instead had a faster-moving squall line that produced less rainfall. Although the degradation of convective forecasts at higher resolution is probably unusual and appears sensitive to the choice of boundary layer parameterization, these findings demonstrate that how numerical models treat boundary layer processes at different grid spacings can, in some cases, have profound influences on predictions of high-impact weather.

scholarly journals A Puzzling Disagreement between Observations and Numerical Models in the Central Gulf of Mexico

2013 ◽  
Vol 43 (12) ◽  
pp. 2673-2681 ◽  
Author(s):  
Wilton Sturges ◽  
Alexandra Bozec
Keyword(s):  
Gulf Of Mexico ◽  
Numerical Models ◽  
Surface Flow ◽  
Return Flow ◽  
Mean Flow ◽  
The West ◽  
Near Surface ◽  
Direct Observations ◽  
Order Of Magnitude ◽  
The Difference

Abstract Two large, independent sets of direct observations in the central Gulf of Mexico show a mean near-surface flow of ~10 cm s−1 to the west, concentrated in the northern and southern Gulf. Numerical models that the authors have examined do not produce this mean westward flow. The observed speeds appear to be almost an order of magnitude larger than the estimated errors; this paper studies the observations to estimate carefully the possible errors involved and compares the observations with model results. The flow to the west in the southern Gulf is presumably wind driven on the shallow parts of the shelf, and, in slightly deeper water at the outer edges of the shelf, is possibly the result of southward Sverdrup interior flow driven by the negative curl of the wind stress. In another possibly related issue, long-term deep current-meter observations in the northern Gulf at ~1000 m and below find flow to the west, whereas some models find flow to the east. The flow proposed here assumes a mean flow to the west above roughly 300 m, with a required return flow in deep water. The difference between the deep observations and the models will produce a slope of pressure surfaces of the opposite sign below 1000 m, reversing the direction of upper-layer geostrophic flow in the models.

scholarly journals The Mean Upper-Layer Flow in the Central Gulf of Mexico by a New Method

2016 ◽  
Vol 46 (10) ◽  
pp. 2915-2924 ◽  
Author(s):  
Wilton Sturges
Keyword(s):  
Gulf Of Mexico ◽  
Numerical Models ◽  
Independent Set ◽  
Sea Surface ◽  
Return Flow ◽  
Mean Flow ◽  
The Mean ◽  
Layer Flow ◽  
A New Technique ◽  
Height Data

AbstractPrevious studies have found a puzzling disagreement between two large datasets and the results of numerical models in the central Gulf of Mexico. The observations suggest an upper-layer mean flow to the west of order 10 cm s−1, while the numerical models find no such mean flow. A new technique is used here, using 23 yr of satellite-derived sea surface height data, to estimate the mean flow. This third, independent set of data yields the same westward flow found in previous studies. These findings require that there be sinking in the western Gulf. The details of the return flow remain an intriguing problem.

Impact of Moisture Transport and Boundary Layer Processes on a Very Severe Cyclonic Storm Using the WRF Model

2019 ◽  
Vol 176 (12) ◽  
pp. 5445-5461 ◽  
Author(s):  
S. S. V. S. Ramakrishna ◽  
Nellipudi Nanaji Rao ◽  
B. Ravi Srinivasa Rao ◽  
P. Srinivasa Rao ◽  
C. V. Srinivas ◽  
...  
Keyword(s):  
Boundary Layer ◽  
Moisture Transport ◽  
Wrf Model ◽  
Cyclonic Storm ◽  
Boundary Layer Processes ◽  
Severe Cyclonic Storm

scholarly journals Improving Radar Refractivity Retrieval by Considering the Change in the Refractivity Profile and the Varying Altitudes of Ground Targets

2016 ◽  
Vol 33 (5) ◽  
pp. 989-1004 ◽  
Author(s):  
Ya-Chien Feng ◽  
Frédéric Fabry ◽  
Tammy M. Weckwerth
Keyword(s):  
Boundary Layer ◽  
Data Quality ◽  
Temporal Change ◽  
Numerical Models ◽  
Vertical Gradient ◽  
Target Range ◽  
Constant Height ◽  
Measured Phase

AbstractAccurate radar refractivity retrievals are critical for quantitative applications, such as assimilating refractivity into numerical models or studying boundary layer and convection processes. However, the technique as originally developed makes some simplistic assumptions about the heights of ground targets () and the vertical gradient of refractivity (). In reality, the field of target phases used for refractivity retrieval is noisy because of varying terrain and introduces estimation biases. To obtain a refractivity map at a constant height above terrain, a 2D horizontal refractivity field at the radar height must be computed and corrected for altitude using an average . This is achieved by theoretically clarifying the interpretation of the measured phase considering the varying and the temporal change of . Evolving causes systematic refractivity biases, as it affects the beam trajectory, the associated target range, and the refractivity field sampled between selected targets of different heights. To determine and changes, a twofold approach is proposed: first, can be reasonably inferred based on terrain height; then, a new method of estimation is devised by using the property of the returned powers of a pointlike target at successive antenna elevations. The obtained shows skill based on in situ tower observation. As a result, the data quality of the retrieved refractivity may be improved with the newly added information of and .

scholarly journals Vertical Velocity Statistics in Fair-Weather Cumuli at the ARM TWP Nauru Climate Research Facility

2010 ◽  
Vol 23 (24) ◽  
pp. 6590-6604 ◽  
Author(s):  
Pavlos Kollias ◽  
Bruce Albrecht
Keyword(s):  
Boundary Layer ◽  
Numerical Models ◽  
Radar Data ◽  
Cloud Fraction ◽  
Cloud Base ◽  
Fair Weather ◽  
Research Facility ◽  
Climate Research ◽  
Velocity Statistics ◽  
Air Motion

Abstract Fair-weather cumuli are fundamental in regulating the vertical structure of water vapor and entropy in the lowest 2–3 km of the earth’s atmosphere over vast areas of the oceans. In this study, a long record of profiling cloud radar observations at the Atmospheric Radiation Measurement Program (ARM) Climate Research Facility (ACRF) at Nauru Island is used to investigate cloud vertical air motion statistics over an 8-yr observing period. Appropriate processing of the observed low radar reflectivities provides radar volume samples that contain only small cloud droplets; thus, the Doppler velocities are used as air motion tracers. The technique is applied to shallow boundary layer clouds (less than 1000 m thick) during the 1999–2007 period when radar data are available. Using the boundary layer winds from the soundings obtained at the Nauru ACRF, the fair-weather cumuli fields are classified in easterly and westerly boundary layer wind regimes. This distinction is necessary to separate marine-forced (westerlies) from land-forced (easterlies) shallow clouds because of a well-studied island effect at the Nauru ACRF. The two regimes exhibit large diurnal differences in cloud fraction and cloud dynamics as manifested by the analysis of the hourly averaged vertical air motion statistics. The fair-weather cumuli fields associated with easterlies exhibit a strong diurnal cycle in cloud fraction and updraft strength and fraction, indicating a strong influence of land-forced clouds. In contrast over the fair-weather cumuli with oceanic origin, land-forced clouds are characterized by uniform diurnal cloudiness and persistent updrafts at the cloud-base level. This study provides a unique observational dataset appropriate for testing fair-weather cumulus mass flux and turbulence parameterizations in numerical models.

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