scholarly journals The Importance of Convective Stage on Out-of-Cloud Convectively Induced Turbulence from High-Resolution Simulations

2020 ◽  
Vol 148 (11) ◽  
pp. 4587-4605
Author(s):  
Katelyn A. Barber ◽  
Gretchen L. Mullendore
Keyword(s):  
High Resolution ◽  
Wind Shear ◽  
Vertical Wind Shear ◽  
Static Stability ◽  
Vertical Wind ◽  
Order Structure ◽  
Air Turbulence ◽  
Turbulence Production ◽  
Prediction Systems ◽  
The Tropics

AbstractTurbulence (clear-air, mountain wave, convectively induced) is an aviation hazard that is a challenge to forecast due to the coarse resolution ultilized in operational weather models. Turbulence indices are commonly used to aid pilots in avoiding turbulence, but these indices have been designed and calibrated for midlatitude clear-air turbulence prediction (e.g., the Ellrod index). A significant limitation with current convectively induced turbulence (CIT) prediction is the lack of storm stage dependency. In this study, six high-resolution simulations of tropical oceanic and midlatitude continental convection are performed to characterize the turbulent environment near various convective types during the developing and mature stages. Second-order structure functions, a diagnostic commonly used to identify turbulence in turbulence prediction systems, are used to characterize the probability of turbulence for various convective types. Turbulence likelihood was found to be independent of region (i.e., tropical vs midlatitude) but dependent on convective stage. The probability of turbulence increased near developing convection for the majority of cases. Additional analysis of static stability and vertical wind shear, indicators of turbulence potential, showed that the convective environment near developing convection was more favorable for turbulence production than mature convection. Near developing convection, static stability decreased and vertical wind shear increased. Vertical wind shear near mature and developing convection was found to be weakly correlated to turbulence intensity in both the tropics and the midlatitudes. This study emphasizes the need for turbulence avoidance guidelines for the aviation community that are dependent on convective stage.

Clear-Air Turbulence Near the Jet-Stream Maxima *

1955 ◽  
Vol 36 (2) ◽  
pp. 53-60 ◽  
Author(s):  
Leroy H. Clem
Keyword(s):  
Wind Speed ◽  
Physical Model ◽  
Wind Shear ◽  
Vertical Wind Shear ◽  
Vertical Wind ◽  
Stability Conditions ◽  
Jet Stream ◽  
Air Turbulence ◽  
Helical Vortices ◽  
High Level

The development of turbo-jet aircraft has made high-level clear air turbulence a major problem for aviation interests. This paper emphasizes the association of the majority of this turbulence with the pronounced vertical wind shear in and near the maximum wind speed centers that move along the jet stream. A physical model is proposed as a possible explanation of clear air turbulence, the associated cirrus bands and wind streaks in the jet maxima. This model is supported by an analogy drawn with similar low-level phenomena studied by Woodcock and others. The model can explain distribution of these features in the horizontal by means of helical vortices which are dependent upon proper vertical wind shear and stability conditions. The observed multiple layers in the vertical are also explained by this model. It is believed that the reason why most of the clear-air turbulence is found near the jet-stream maxima is simply because the necessary shear and stability conditions associated with this turbulence are most frequently fulfilled in that region.

Misocyclone Characteristics along Florida Gust Fronts during CaPE

2005 ◽  
Vol 133 (11) ◽  
pp. 3345-3367 ◽  
Author(s):  
Katja Friedrich ◽  
David E. Kingsmill ◽  
Carl R. Young
Keyword(s):  
Wind Shear ◽  
Doppler Radar ◽  
Vertical Wind Shear ◽  
Static Stability ◽  
Vertical Wind ◽  
Horizontal Wind ◽  
Gust Fronts ◽  
Convection Initiation ◽  
The Relationship ◽  
Gust Front

Abstract Multiple-Doppler radar and rawinsonde data are used to examine misocyclone characteristics along gust fronts observed during the Convection and Precipitation/Electrification (CaPE) project in Florida. The objective of this study is to investigate the observational representativeness of previous numerical simulations of misocyclones by employing a consistent analysis strategy to 11 gust fronts observed in the same region. The investigation focuses on the intensity range of misocyclones and their organization along gust fronts; the relationship between misocyclone intensity and horizontal wind shear, vertical wind shear, and static stability; and the relationship between misocyclones and convection initiation. The intensity of misocyclones, as indicated by the maximum values of vertical vorticity, varied from 2.8 × 10−3 to 13.9 × 10−3 s−1, although all but one case exhibited values less than 6.4 × 10−3 s−1. Organized misocyclone patterns were only found along small segments of gust fronts. Within those segments misocyclones were spaced between 3 and 7 km. Results show that the intensity of misocyclones was most closely related to the strength of horizontal wind shear across the gust front. The relationship between misocyclone intensity and vertical wind shear and static stability was not as clear. Although convection was initiated along the gust front in 7 of the 11 cases, those regions were not collocated with or in close proximity to misocyclones.

High-Resolution Observations of a Destructive Macroburst

2021 ◽  
Author(s):  
Samuel J. Childs ◽  
Russ S. Schumacher ◽  
Rebecca D. Adams-Selin
Keyword(s):  
High Resolution ◽  
Wind Shear ◽  
Vertical Wind Shear ◽  
Vertical Wind ◽  
Convective System ◽  
Wind Gust ◽  
Damage Survey ◽  
Strong Inversion ◽  
Radial Outflow ◽  
The Town

AbstractShortly after 0600 UTC (midnight MDT) on 9 June 2020, a rapidly intensifying and elongating convective system produced a macroburst and extensive damage in the town of Akron on Colorado’s eastern Plains. Instantaneous winds were measured as high as 51.12 m s−1 at 2.3 m AGL from an eddy covariance (EC) tower, and a 50.45 m s−1 wind gust from an adjacent 10-m tower became the highest official thunderstorm wind gust ever measured in Colorado. Synoptic-scale storm motion was southerly, but surface winds were northerly in a post-frontal airmass, creating strong vertical wind shear. Extremely high-resolution temporal and spatial observations allow for a unique look at pressure and temperature tendencies accompanying the macroburst and reveal intriguing wave structures in the outflow. At 10-Hz frequency, the EC tower recorded a 5-hPa pressure surge in 19 seconds immediately following the strongest winds, and a 15-hPa pressure drop in the following three minutes. Surface temperature also rose 1.5°C in less than one minute, concurrent with the maximum wind gusts, and then fell sharply by 3.5°C in the following minute. Shifting wind direction observations and an NWS damage survey are suggestive of both radial outflow and a gust front passage, and model proximity soundings reveal a well-mixed surface layer topped by a strong inversion and large low-level vertical wind shear. Despite the greatest risk of severe winds forecast to be northeast of Colorado, convection-allowing model forecasts from 6-18 h in advance did show similar structures to what occurred, warranting further simulations to investigate the unique mesoscale and misoscale features associated with the macroburst.

Future Impact of Differential Interbasin Ocean Warming on Atlantic Hurricanes

2011 ◽  
Vol 24 (4) ◽  
pp. 1264-1275 ◽  
Author(s):  
Sang-Ki Lee ◽  
David B. Enfield ◽  
Chunzai Wang
Keyword(s):  
Wind Shear ◽  
Climate Model ◽  
Global Climate ◽  
Global Climate Model ◽  
Vertical Wind Shear ◽  
Static Stability ◽  
Vertical Wind ◽  
First Century ◽  
Greenhouse Warming ◽  
Twenty First Century

Abstract Global climate model simulations forced by future greenhouse warming project that the tropical North Atlantic (TNA) warms at a slower rate than the tropical Indo-Pacific in the twenty-first century, consistent with their projections of a weakened Atlantic thermohaline circulation. Here, an atmospheric general circulation model is used to advance a consistent physical rationale that the suppressed warming of the TNA increases the vertical wind shear and static stability aloft in the main development region (MDR) for Atlantic hurricanes, and thus decreases overall Atlantic hurricane activity in the twenty-first century. A carefully designed suite of model experiments illustrates that the preferential warming of the tropical Indo-Pacific induces a global average warming of the tropical troposphere, via a tropical teleconnection mechanism, and thus increases atmospheric static stability and decreases convection over the suppressed warming region of the TNA. The anomalous diabatic cooling, in turn, forces the formation of a stationary baroclinic Rossby wave northwest of the forcing region, consistent with Gill’s simple model of tropical atmospheric circulations, in such a way as to induce a secular increase of the MDR vertical wind shear. However, a further analysis indicates that the net effect of future greenhouse warming on the MDR vertical wind shear is less than the observed multidecadal swing of the MDR vertical wind shear in the twentieth century. Thus, it is likely that the Atlantic multidecadal oscillation will still play a decisive role over the greenhouse warming in the fate of Atlantic hurricane activity throughout the twenty-first century under the assumption that the twenty-first-century changes in interbasin SST difference, projected by the global climate model simulations, are accurate.

A Case Study of the Jet Stream

1955 ◽  
Vol 36 (5) ◽  
pp. 195-203 ◽  
Author(s):  
Robert R. Dickson
Keyword(s):  
High Velocity ◽  
Wind Shear ◽  
Vertical Wind Shear ◽  
Indirect Evidence ◽  
Vertical Wind ◽  
Jet Stream ◽  
Absolute Vorticity ◽  
Pressure Surface ◽  
Air Turbulence

Data, acquired by specially instrumented aircraft, are presented for two levels through a northwesterly jet stream. Wind shear on the cyclonic side of this jet stream is roughly twice that on the anticyclonic side. Stronger areas of clear air turbulence appear closely related to strong vertical wind shear. An area of uniform absolute vorticity exists for about 160 nautical miles north of the jet stream. Measured microvariations of the temperature along a pressure surface—up to 3.1 C° in 8.5 nautical miles—give indirect evidence of jet stream “fingers” of high velocity.

On the Slope of Low-pressure Axes as a Criterion for Deepening in the Tropics

1948 ◽  
Vol 29 (1) ◽  
pp. 9-15
Author(s):  
R. H. Simpson
Keyword(s):  
Pacific Ocean ◽  
Tropical Cyclones ◽  
Wind Shear ◽  
Vertical Wind Shear ◽  
Low Pressure ◽  
Vertical Wind ◽  
Vertical Shear ◽  
The Pacific ◽  
The Pacific Ocean ◽  
The Tropics

The relation between the slope of tropical low pressure axes and the tendency for such lows to deepen or fill has been studied during investigations carried on separately in the Atlantic and in the Pacific ocean areas. The preliminary conclusions drawn from each of the two studies differ considerably and are reviewed herein. Limitations upon the use of vertical wind shear computations in determining the slope of such pressure axes are discussed. Questions are raised regarding the assumption in such computations that the vertical shear of the observed wind is a good approximation of the shear of the geostrophic components. Illustrations are given of the fallacies of reasoning that may result from such an assumption in connection with tropical cyclones.

How Does the Eye Warm? Part II: Sensitivity to Vertical Wind Shear and a Trajectory Analysis

2013 ◽  
Vol 70 (7) ◽  
pp. 1849-1873 ◽  
Author(s):  
Daniel P. Stern ◽  
Fuqing Zhang
Keyword(s):  
Tropical Cyclones ◽  
Wind Shear ◽  
Vertical Wind Shear ◽  
Static Stability ◽  
Vertical Wind ◽  
Strong Function ◽  
Upper Troposphere ◽  
Warm Core ◽  
Sufficient Intensity ◽  
Insight Into

Abstract In Part II of this study, idealized simulations of tropical cyclones are used to investigate the influence of vertical wind shear on the structure of warming and descent in the eye; results are compared with the no-shear simulation that was analyzed in Part I. During intensification of a tropical cyclone in a quiescent environment, time-averaged eye descent is maximized at 12–13-km height. Warming is not generally maximized at these levels, however, because the static stability is at a minimum. Consequently, the perturbation temperature is maximized at midlevels. Each of the above results remains valid for sheared tropical cyclones, and therefore shear does not systematically alter the height of the warm core. An analysis of over 90 000 parcel trajectories yields further insight into the mechanisms of eye warming and addresses several outstanding questions regarding the character of eye descent. The rate at which parcels are stirred from the eye into the eyewall is a strong function of intensity. While stirring is large at the beginning of rapid intensification (RI), once a sufficient intensity is achieved, most parcels originating near the storm center can remain inside the eye for at least several days. Many parcels in the upper troposphere are able to descend within the eye by 5–10 km. The above results are relatively insensitive to the presence of up to 10 m s−1 of shear. In contrast, stirring in the eye–eyewall interface region is substantially enhanced by shear.

scholarly journals A Numerical Study on the Extreme Intensification of Hurricane Patricia (2015)

2018 ◽  
Vol 33 (4) ◽  
pp. 989-999 ◽  
Author(s):  
K. Ryder Fox ◽  
Falko Judt
Keyword(s):  
High Resolution ◽  
Surface Temperature ◽  
Sea Surface Temperature ◽  
Wind Shear ◽  
Extreme Event ◽  
Numerical Study ◽  
Weather Prediction ◽  
Vertical Wind Shear ◽  
Vertical Wind ◽  
Sea Surface

Abstract In October 2015 Hurricane Patricia stormed through the eastern Pacific, taking its place as the strongest hurricane in recorded history when its intensity reached a record breaking 185 kt (1 kt = 0.51 m s−1). Operational models and the National Hurricane Center’s official forecast failed to predict Patricia’s unprecedented intensification, provoking questions as to whether such an extreme event can actually be forecast. This study reports on the successful simulation of Patricia using a state-of-the-art high-resolution numerical weather prediction model. It was found that high model resolution (Δx ≤ 1 km), vortex initialization, and the parameterization of dissipative heating were key factors in realistically simulating Patricia’s intensity evolution. The simulation was used to investigate Patricia’s environment in terms of sea surface temperature, vertical wind shear, and humidity, under the premise that a simulation able to capture Patricia’s peak intensity would also accurately represent Patricia’s environment. Compared with a climatology derived from the Statistical Hurricane Intensity Prediction Scheme dataset, sea surface temperature ranked in the 99th percentile and environmental vertical wind shear in the 83rd percentile (ordered from high to low). However, humidity ranked more moderately. Ensemble forecasts indicate that Patricia had relatively high predictability in comparison to other well-studied rapid intensification cases such as 2010’s Hurricane Earl. The results from this study imply that high-resolution models are in principle able to predict the intensity of extreme hurricanes like Patricia.

Atlantic Subtropical Storms. Part II: Climatology

2009 ◽  
Vol 22 (13) ◽  
pp. 3574-3594 ◽  
Author(s):  
Mark P. Guishard ◽  
Jenni L. Evans ◽  
Robert E. Hart
Keyword(s):  
Tropical Cyclones ◽  
North Atlantic ◽  
Wind Shear ◽  
Vertical Wind Shear ◽  
Warm Season ◽  
Rapid Onset ◽  
Static Stability ◽  
Hybrid Structure ◽  
Vertical Wind ◽  
Tropical Cyclogenesis

Abstract A 45-yr climatology of subtropical cyclones (ST) for the North Atlantic is presented and analyzed. The STs pose a warm-season forecasting problem for subtropical locations such as Bermuda and the southern United States because of the potentially rapid onset of gale-force winds close to land. Criteria for identification of ST have been developed based on an accompanying case-study analysis. These criteria are applied here to the 40-yr European Centre for Medium-Range Weather Forecasts Re-Analysis (ERA-40) to construct a consistent historical database of 197 North Atlantic ST in 45 yr. Because ST may eventually evolve into tropical cyclones, sea surface temperatures (SST) and vertical wind shear conditions for tropical cyclogenesis are contrasted with the conditions for ST genesis identified here. Around 60% of the 197 ST formed over SST in excess of 25°C in a region of weak static stability. Further, the mean environmental vertical wind shear at formation for these storms is 10.7 m s−1, a magnitude generally considered to be unfavorable for tropical cyclogenesis. The STs have hybrid structure, so the potential for baroclinic and thermodynamic development is explored through the baroclinic zone (characterized by the Eady growth rate σ) and SST field. Seasonal evolution in the location and frequency of ST formation in the basin is demonstrated to correspond well to the changing region of overlap between SST > 25°C and σ > 0.1 day−1. This climatology is contrasted with two alternative ST datasets. The STs contribute to 12% of tropical cyclones (TC) in the current National Hurricane Center (NHC) Hurricane Database (HURDAT); this equivalent to about 1 in 8 genesis events from an incipient ST disturbance. However, with the addition of 144 ST that are newly identified in this climatology (and not presently in HURDAT) and the reclassification (as not ST) of 65 existing storms in HURDAT, 197/597 storms (33%) in the newly combined database are ST, which emphasizes the potential importance of these warm-season storms.

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