Ground‐based measurements and dual‐Doppler analysis of 3‐D wind fields and atmospheric circulations induced by a meso‐<i>γ</i>‐scale inland lake

Asefi-Najafabady, Salvi; Knupp, Kevin R.; Mecikalski, John R.; Welch, Ronald M.; Phillips, Dustin

doi:10.1029/2010jd014022

Cited by 16 publications

(18 citation statements)

References 33 publications

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“…1) capable of inducing localized solenoidal circulations along the edges of the EVAD radius. For example, Asefi-Najafabady et al (2010) describe the development of a local lake-breeze circulation that regularly occurs along the lake 20 km west of ARMOR. Such localized features may partially account for the nearly symmetric range in convergence values found, but further investigation would be required to state this definitively.…”

Section: Horizontal Wind Speed and Convergencementioning

confidence: 99%

Multi-platform Observations Characterizing the Afternoon-to-Evening Transition of the Planetary Boundary Layer in Northern Alabama, USA

Wingo

Knupp

2014

Boundary-Layer Meteorol

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Observations from the University of Alabama in Huntsville campus and groundbased scanning radar for over 140 total spring, summer, and autumn cases are studied to contribute to the relative scarcity of long-term datasets documenting the afternoon-to-evening transition of the planetary boundary layer. A sunset relative frame of reference is employed, focusing on the period 3 h before to 2 h after astronomical sunset, and several findings are consistent with previous investigations. Fluctuating components of wind and temperature computed from nearly collocated surface, Doppler wind profiler, and vertically pointing Doppler lidar measurements show a consistent decline as turbulence intensity diminishes through the transition. When normalized by their initial values, a pattern emerges: temperature variances decline slowly at first then quite abruptly after about 90 min before sunset. After the temperature variances begin to wane, vertical velocity fluctuations decrease, and the rate of their decay increases as vigorous thermal structures diminish. The fastest decline of the horizontal wind variance occurs after an accelerated vertical wind variance decrease, and the horizontal wind fluctuations display the slowest rate of decrease among these quantities. Near-surface humidity measurements show increases in mean water vapour mixing ratio as a steady rise generally beginning about 80 min prior to sunset. Composites of mean lidar vertical motion show final convective-type towers of upward motion occur about an hour before sunset and are coherent through 800 m (all heights a.g.l.). Lidar vertical motion variance at 195 m decreases by more than an order of magnitude approaching sunset, then remains below 0.01 m 2 s −2 for the rest of the studied time frame. Subtle, but steady, increases in both horizontal wind speed and radar-derived horizontal wind convergence above the surface layer (at 300 m) span the entire 5-h time frame. While the convergence results show a broad range, an increase in the mean is clear and found to be statistically significant. Implications

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Section: Horizontal Wind Speed and Convergencementioning

confidence: 99%

Multi-platform Observations Characterizing the Afternoon-to-Evening Transition of the Planetary Boundary Layer in Northern Alabama, USA

Wingo

Knupp

2014

Boundary-Layer Meteorol

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“…Mobile radars seem to be particularly well suited for the observation of tornadoes owing to their ability to maximize spatial resolution (by reducing the distance between radar and tornado), and they can typically provide greater volumetric coverage near the ground compared to the coverage provided by most nonmobile radar systems (which typically sample tornadoes at greater ranges owing to their nonmobile nature). In the past decade, the number of mobile radars available for research has increased significantly; such platforms include the rapid-scan, X-band, polarimetric radar (RaXPol; Pazmany et al 2013); the Mobile Weather Radar 2005 X-band phased-array radar (MWR-05XP; Bluestein et al 2010); the Doppler on Wheels radars (DOWs; Wurman et al 1997); the National Oceanic and Atmospheric Administration (NOAA) X-band polarimetric radar (NOXP or XERES; Melnikov et al 2009); the Texas Tech University Ka-band radars (TTU-Ka; Weiss et al 2011); and the Mobile, Alabama, Xband radar (MAX; Asefi-Najafabady et al 2010). Rather uniquely, the antennas on RaXPol and MWR05XP are mounted on pedestals that can rotate up to 1808 s 21 , producing a 3608 sweep every 2 s; this increased temporal resolution is extremely useful when probing tornadoes and other rapidly changing phenomena.…”

Section: Introductionmentioning

confidence: 99%

Some Considerations for the Use of High-Resolution Mobile Radar Data in Tornado Intensity Determination

Snyder

Bluestein

2014

Weather and Forecasting

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The increasing number of mobile Doppler radars used in field campaigns across the central United States has led to an increasing number of high-resolution radar datasets of strong tornadoes. There are more than a few instances in which the radar-measured radial velocities substantially exceed the estimated wind speeds associated with the enhanced Fujita (EF) scale rating assigned to a particular tornado. It is imperative, however, to understand what the radar data represent if one wants to compare radar observations to damagebased EF-scale estimates. A violent tornado observed by the rapid-scan, X-band, polarimetric mobile radar (RaXPol) on 31 May 2013 contained radar-relative radial velocities exceeding 135 m s 21 in rural areas essentially devoid of structures from which damage ratings can be made. This case, along with others, serves as an excellent example of some of the complications that arise when comparing radar-estimated velocities with the criteria established in the EF scale. In addition, it is shown that data from polarimetric radars should reduce the variance of radar-relative radial velocity estimates within the debris field compared to data from single-polarization radars. Polarimetric radars can also be used to retrieve differential velocity, large magnitudes of which are spatially associated with large spectrum widths inside the polarimetric tornado debris signature in several datasets of intense tornadoes sampled by RaXPol.

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“…However, as mentioned above, the combination of land cover types and topography gradient likely contributes to CC development and growth by forming mesoscale circulations similar to those of sea breezes, as a result of contrasting land surfaces (Walker et al 2009;Asefi-Najafabady et al 2010). 2) CC development over urban areas was high once ocean pixels were removed from the analysis in the subset.…”

Section: Discussionmentioning

confidence: 99%

A Satellite-Based Summer Convective Cloud Frequency Analysis over the Southeastern United States

Gambill¹,

Mecikalski²

2011

Journal of Applied Meteorology and Climatology

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A convective cloud (CC) analysis is performed over the southeastern United States (SEUS) during June, July, and August 2006 and 2007, using data from the Geostationary Operational Environmental Satellite (GOES) visible and infrared sensors as processed by a satellite-based convection cloud mask and initiation algorithm. Six 5-7-day periods are analyzed between the times 1500 and 1900 UTC, representative of summertime conditions in the SEUS. The ;8.7 3 10 8 pixel database contains information on nonprecipitating CCs possessing various satellite-estimated attributes of cloud size, based on whether they meet set thresholds in eight infrared ''interest fields.'' CCs at ;1 km 3 1 km pixel size in the GOES projection are evaluated in comparison with the land cover classes, elevation gradients, and normalized difference vegetation indices (NDVIs) beneath the CCs. The goals are to relate the frequency of occurrence of CCs to land surface properties, attempting to determine which of these three properties are most correlated with CCs. CCs are more likely to form over forests and dense vegetation and over higher gradients in elevation. Although forest cover classes are not the most common over the SEUS, CC occurrence increases disproportionately where steeply sloped topography and forests are coincident across large regions of the SEUS. Also, as NDVI increases, the percentage of CCs per land class also increases. Analysis of landscape heterogeneity (combining local variability in land classes, topography, and NDVI) shows that as it increases CC development is more widespread. Thus, lakes among forests and hilly topography intermingled with agricultural lands appear most conducive to high CC frequency.

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Ground‐based measurements and dual‐Doppler analysis of 3‐D wind fields and atmospheric circulations induced by a meso‐γ‐scale inland lake

Cited by 16 publications

References 33 publications

Multi-platform Observations Characterizing the Afternoon-to-Evening Transition of the Planetary Boundary Layer in Northern Alabama, USA

Multi-platform Observations Characterizing the Afternoon-to-Evening Transition of the Planetary Boundary Layer in Northern Alabama, USA

Some Considerations for the Use of High-Resolution Mobile Radar Data in Tornado Intensity Determination

A Satellite-Based Summer Convective Cloud Frequency Analysis over the Southeastern United States

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