A Numerical Simulation of Convectively Induced Turbulence above Deep Convection

AbstractAt 1034 UTC 2 September 2007, a commercial aircraft flying from Jeju, South Korea, to Osaka, Japan, at an altitude of approximately 11.2 km encountered severe turbulence above deep convection. To investigate the characteristics and generation mechanism of this event, the real atmosphere is simulated using the Weather Research and Forecasting model with six nested domains, the finest of which is a horizontal grid spacing of 120 m. The model reproduces well the observed large-scale flows and the location and timing of the turbulence along the evolving deep convection. Three hours before the incident, isolated deep convection with two overshooting tops develops in a warm area ahead of the cold front in the southwestern region of the turbulence. As the deep convection moves with the dominant southwesterly flow toward the incident region, its thickness shrinks significantly because of weakening of upward motions inside the convection. Twenty minutes before the incident, the dissipating convection disturbs the southwesterly flow at the incident altitude, enhancing local vertical wind shear above the dissipating convection. The leading edge of the cloud stretches toward the lee side because of shear-induced y vorticity, finally overturning. This activates turbulence and vertical mixing at the cloud boundary through convective instability in the entrainment process. While the dissipating convection, its thickness still shrinking, continues to move toward the observed turbulence region, the turbulence generated at the cloud interface is advected by the dominant southwesterly flow, emerging about 1–2 km above the dissipating convection and intersecting the aircraft’s flight route at the incident time.

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Modeling the Ocean in Climate Studies

Annals of Glaciology ◽

10.3189/1984aog5-1-133-140 ◽

1984 ◽

Vol 5 ◽

pp. 133-140 ◽

Cited By ~ 2

Author(s):

Albert J. Semtner

Keyword(s):

Turbulent Mixing ◽

Large Scale ◽

Deep Convection ◽

Vertical Mixing ◽

Mesoscale Eddies ◽

Small Scale ◽

Polar Regions ◽

Sea Ice Extent ◽

Modeling Strategy ◽

Climate Studies

A number of processes in the ocean must be modeled properly in order to produce valid estimates of oceanic heat transport, sea-surface temperature, and sea-ice extent in climate studies. These include: wind-driven turbulent mixing and water transport in the surface layer, internal vertical mixing due to several small-scale mechanisms, horizontal and vertical exchanges by mesoscale eddies, mixing along isopycnals, large-scale transport by currents, deep convection in polar regions, and boundary exchanges with atmosphere, ice, and land. Techniques to model these processes are described. Prospects are given for parameterizing the effects of phenomena that cannot be resolved in climate studies, particularly mesoscale eddies. Past simulations of the ocean in climate studies are reviewed. A modeling strategy is outlined for an improved treatment of the ocean, consistent with the computational power soon to be available.

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Effects of Boundary Layer Vertical Mixing on the Evolution of Hurricanes over Land

Monthly Weather Review ◽

10.1175/mwr-d-16-0421.1 ◽

2017 ◽

Vol 145 (6) ◽

pp. 2343-2361 ◽

Cited By ~ 7

Author(s):

Feimin Zhang ◽

Zhaoxia Pu ◽

Chenghai Wang

Keyword(s):

Boundary Layer ◽

Positive Impact ◽

Potential Temperature ◽

Vertical Mixing ◽

Vertical Wind Shear ◽

Vertical Gradient ◽

Weather Research And Forecasting ◽

Virtual Potential Temperature ◽

Dynamic Structures ◽

Hurricane Boundary Layer

Abstract After a hurricane makes landfall, its evolution is strongly influenced by its interaction with the planetary boundary layer (PBL) over land. In this study, a series of numerical experiments are performed to examine the effects of boundary layer vertical mixing on hurricane simulations over land using a research version of the NCEP Hurricane Weather Research and Forecasting (HWRF) Model with three landfalling hurricane cases. It is found that vertical mixing in the PBL has a strong influence on the simulated hurricane evolution. Specifically, strong vertical mixing has a positive impact on numerical simulations of hurricanes over land, with better track, intensity, synoptic flow, and precipitation simulations. In contrast, weak vertical mixing leads to the strong hurricanes over land. Diagnoses of the thermodynamic and dynamic structures of hurricane vortices further suggest that the strong vertical mixing in the PBL could cause a decrease in the vertical wind shear and an increase in the vertical gradient of virtual potential temperature. As a consequence, these changes destroy the turbulence kinetic energy in the hurricane boundary layer and thus stabilize the hurricane boundary layer and limit its maintenance over land.

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Four Years of Tropical ERA-40 Vorticity Maxima Tracks. Part II: Differences between Developing and Nondeveloping Disturbances

Monthly Weather Review ◽

10.1175/2008mwr2545.1 ◽

2009 ◽

Vol 137 (8) ◽

pp. 2576-2591 ◽

Cited By ~ 23

Author(s):

Brandon Kerns ◽

Edward Zipser

Keyword(s):

Large Scale ◽

Deep Convection ◽

Vertical Wind Shear ◽

Skill Score ◽

Relative Vorticity ◽

Prediction Skill ◽

Tropical Cyclogenesis ◽

Linear Discriminant ◽

Predictive Skill ◽

Heidke Skill Score

Abstract Using a subset of the relative vorticity maxima (VM) tracks described in Part I, large-scale environmental fields, cold cloud area, and rainfall area are used to discriminate between developing and nondeveloping tropical disturbances in the eastern North Pacific (EPAC) and Atlantic Oceans. By using a minimum cold cloud coverage requirement, the nondeveloping VM are limited to disturbances with enhanced low-level relative vorticity and widespread deep convection. Linear discriminant analysis is used to determine the overall discrimination and the relative importance of each predictor for each basin separately. It is important to distinguish the two basins because, for many predictors, the differences between the basins are greater than the differences between developing and nondeveloping VM in each basin. Using the parametric forecast method, there is greater discrimination and prediction skill in the EPAC than in the Atlantic. There are also significant differences between the two basins in terms of the degree of discrimination provided by each of the predictors. Surprisingly, the mean vertical wind shear magnitude is greater for EPAC developing VM than for EPAC nondeveloping VM. Incorporating the satellite-derived predictors marginally improves the potential forecast skill in the EPAC but not in the Atlantic. The prediction skill (Heidke skill score) of tropical cyclogenesis in the Atlantic is similar to what has been obtained in previous studies using cloud cluster tracks. There is greater predictive skill in the EPAC.

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Observations and Simulation of Elevated Nocturnal Convection Initiation on 24 June 2015 during PECAN

Monthly Weather Review ◽

10.1175/mwr-d-19-0218.1 ◽

2020 ◽

Vol 148 (2) ◽

pp. 613-635 ◽

Cited By ~ 3

Author(s):

Stanley B. Trier ◽

Scott D. Kehler ◽

John Hanesiak

Keyword(s):

Large Scale ◽

Deep Convection ◽

Leading Edge ◽

Radiosonde Data ◽

Local Cooling ◽

Surface Front ◽

Westerly Flow ◽

Vertical Displacements ◽

Upward Displacement ◽

Convection Initiation

Abstract The environment of elevated nocturnal deep convection initiation (CI) on 24 June 2015 is investigated using radiosonde data from the Plains Elevated Convection at Night (PECAN) field experiment and a convection-allowing simulation. Elevated CI occurs around midnight in ascending westerly flow above the northeastern terminus of the nocturnal low-level jet (LLJ) several hundred kilometers poleward of the leading edge of a surface warm front. This CI originates from within preexisting banded altocumulus clouds that are supported by persistent large-scale ascent within the entrance region of a midtropospheric jet streak. Model trajectories calculated backward from convective updraft cores during CI indicate abrupt lifting at the leading edge of the surface front during the late afternoon to altitudes above that of the subsequent southerly LLJ. This air remains significantly subsaturated during northward movement until after several hours of weaker but persistent ascent within the highly elevated westerly airstream during the evening. Unlike in many previous studies of frontal overrunning by the LLJ, strong local drying occurs within the LLJ core. Nevertheless, vertical displacements from persistent mesoscale ascent were sufficient for trajectory air parcels to reach their LFC and sustain deep convection. The mesoscale upward displacement along trajectories is well explained by isentropic upglide associated with frontal overrunning at horizontal distances greater than 100 km from the CI and subsequent mature convection. However, the significant additional mesoscale vertical displacements needed for deep CI to occur in the westerlies above the horizontally convergent ~100-km-wide LLJ terminus region, were associated with local cooling and are not accounted for by steady isentropic upglide.

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Prediction and Diagnosis of Tropical Cyclone Formation in an NWP System. Part III: Diagnosis of Developing and Nondeveloping Storms

Journal of the Atmospheric Sciences ◽

10.1175/jas4023.1 ◽

2007 ◽

Vol 64 (9) ◽

pp. 3195-3213 ◽

Cited By ~ 25

Author(s):

K. J. Tory ◽

N. E. Davidson ◽

M. T. Montgomery

Keyword(s):

Tropical Cyclone ◽

Large Scale ◽

Deep Convection ◽

Weather Prediction ◽

Vertical Wind Shear ◽

Forecast Model ◽

Vertical Shear ◽

Limited Area ◽

Vortex Interactions ◽

Secondary Mechanism

Abstract This is the third of a three-part investigation into tropical cyclone (TC) genesis in the Australian Bureau of Meteorology’s Tropical Cyclone Limited Area Prediction System (TC-LAPS), an operational numerical weather prediction (NWP) forecast model. In Parts I and II, a primary and two secondary vortex enhancement mechanisms were illustrated, and shown to be responsible for TC genesis in a simulation of TC Chris. In this paper, five more TC-LAPS simulations are investigated: three developing and two nondeveloping. In each developing simulation the pathway to genesis was essentially the same as that reported in Part II. Potential vorticity (PV) cores developed through low- to middle-tropospheric vortex enhancement in model-resolved updraft cores (primary mechanism) and interacted to form larger cores through diabatic upscale vortex cascade (secondary mechanism). On the system scale, vortex intensification resulted from the large-scale mass redistribution forced by the upward mass flux, driven by diabatic heating, in the updraft cores (secondary mechanism). The nondeveloping cases illustrated that genesis can be hampered by (i) vertical wind shear, which may tilt and tear apart the PV cores as they develop, and (ii) an insufficient large-scale cyclonic environment, which may fail to sufficiently confine the warming and enhanced cyclonic winds, associated with the atmospheric adjustment to the convective updrafts. The exact detail of the vortex interactions was found to be unimportant for qualitative genesis forecast success. Instead the critical ingredients were found to be sufficient net deep convection in a sufficiently cyclonic environment in which vertical shear was less than some destructive limit. The often-observed TC genesis pattern of convection convergence, where the active convective regions converge into a 100-km-diameter center, prior to an intense convective burst and development to tropical storm intensity is evident in the developing TC-LAPS simulations. The simulations presented in this study and numerous other simulations not yet reported on have shown good qualitative forecast success. Assuming such success continues in a more rigorous study (currently under way) it could be argued that TC genesis is largely predictable provided the large-scale environment (vorticity, vertical shear, and convective forcing) is sufficiently resolved and initialized.

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Warm Rain in Southern West Africa: A Case Study at Savè

Atmosphere ◽

10.3390/atmos11030298 ◽

2020 ◽

Vol 11 (3) ◽

pp. 298

Author(s):

Irene Reinares Martínez ◽

Jean-Pierre Chaboureau ◽

Jan Handwerker

Keyword(s):

West Africa ◽

Large Scale ◽

Initial Conditions ◽

Deep Convection ◽

Vertical Wind Shear ◽

Radar Observations ◽

Eddy Simulation ◽

Vertical Extension ◽

Warm Rain ◽

Almost All

A warm-rain episode over southern West Africa is analyzed using unprecedented X-band radar observations from Savè, Benin and a Large-Eddy Simulation (LES) over a 240 × 240 km 2 domain. While warm rain contributes to 1% of the total rainfall in the LES, its spatial extent accounts for 24% of the area covered by rainfall. Almost all the warm-rain cells tracked in the observation and the LES have a size between 2 and 10 km and a lifetime varying from 5 to 60 min. During the nighttime, warm-rain cells are caused by the dissipation of large deep-convection systems while during the daytime they are formed by the boundary-layer thermals. The vertical extension of the warm-rain cells is limited by vertical wind shear at their top. In the simulation, their top is 1.6 km higher with respect to the radar observations due to the large-scale environment given by wrong initial conditions. This study shows the challenge of simulating warm rain in southern West Africa, a key phenomenon during the little dry season.

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Rapid Scan Views of Convectively Generated Mesovortices in Sheared Tropical Cyclone Gustav (2002)

Weather and Forecasting ◽

10.1175/waf950.1 ◽

2006 ◽

Vol 21 (6) ◽

pp. 1041-1050 ◽

Cited By ~ 11

Author(s):

Eric A. Hendricks ◽

Michael T. Montgomery

Keyword(s):

Large Scale ◽

Deep Convection ◽

Level Structure ◽

Vertical Wind Shear ◽

Vertical Shear ◽

Low Level ◽

Rapid Scan ◽

Mesoscale Processes ◽

Vertical Shearing

Abstract On 9–10 September 2002, multiple mesovortices were captured in great detail by rapid scan visible satellite imagery in subtropical, then later, Tropical Storm Gustav. These mesovortices were observed as low-level cloud swirls while the low-level structure of the storm was exposed due to vertical shearing. They are shown to form most plausibly via vortex tube stretching associated with deep convection; they become decoupled from the convective towers by vertical shear; they are advected with the low-level circulation; finally they initiate new hot towers on their boundaries. Partial evidence of an axisymmetrizing mesovortex and its hypothesized role in the parent vortex spinup is presented. Observations from the mesoscale and synoptic scale are synthesized to provide a multiscale perspective of the intensification of Gustav that occurred on 10 September. The most important large-scale factors were the concurrent relaxation of the 850–200-hPa-deep layer vertical wind shear from 10–15 to 5–10 m s−1 and movement over pockets of very warm sea surface temperatures (approximately 29.5°–30.5°C). The mesoscale observations are not sufficient alone to determine the precise role of the deep convection and mesovortices in the intensification. However, qualitative comparisons are made between the mesoscale processes observed in Gustav and recent full-physics and idealized numerical simulations to obtain additional insight.

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Modeling the Ocean in Climate Studies

Annals of Glaciology ◽

10.1017/s0260305500003633 ◽

1984 ◽

Vol 5 ◽

pp. 133-140 ◽

Cited By ~ 5

Author(s):

Albert J. Semtner

Keyword(s):

Turbulent Mixing ◽

Large Scale ◽

Deep Convection ◽

Vertical Mixing ◽

Mesoscale Eddies ◽

Small Scale ◽

Polar Regions ◽

Sea Ice Extent ◽

Modeling Strategy ◽

Climate Studies

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An Ensemble Approach to Investigate Tropical Cyclone Intensification in Sheared Environments. Part II: Ophelia (2011)

Journal of the Atmospheric Sciences ◽

10.1175/jas-d-15-0245.1 ◽

2016 ◽

Vol 73 (4) ◽

pp. 1555-1575 ◽

Cited By ~ 20

Author(s):

Rosimar Rios-Berrios ◽

Ryan D. Torn ◽

Christopher A. Davis

Keyword(s):

Tropical Cyclone ◽

Large Scale ◽

Inner Core ◽

Deep Convection ◽

Three Dimensional ◽

Vertical Wind Shear ◽

Wind Fields ◽

Convective Scale ◽

Intensity Changes ◽

Large Scale Flow

Abstract The mechanisms leading to tropical cyclone (TC) intensification amid moderate vertical wind shear can vary from case to case, depending on the vortex structure and the large-scale conditions. To search for similarities between cases, this second part investigates the rapid intensification of Hurricane Ophelia (2011) in an environment characterized by 200–850-hPa westerly shear exceeding 8 m s−1. Similar to Part I, a 96-member ensemble was employed to compare a subset of members that predicted Ophelia would intensify with another subset that predicted Ophelia would weaken. This comparison revealed that the intensification of Ophelia was aided by enhanced convection and midtropospheric moisture in the downshear and left-of-shear quadrants. Enhanced left-of-shear convection was key to the establishment of an anticyclonic divergent outflow that forced a nearby upper-tropospheric trough to wrap around Ophelia. A vorticity budget showed that deep convection also contributed to the enhancement of vorticity within the inner core of Ophelia via vortex stretching and tilting of horizontal vorticity enhanced by the upper-tropospheric trough. These results suggest that TC intensity changes in sheared environments and in the presence of upper-tropospheric troughs highly depend on the interaction between convective-scale processes and the large-scale flow. Given the similarities between Part I and this part, the results suggest that observations from the three-dimensional moisture and wind fields could improve both forecasting and understanding of TC intensification in moderately sheared environments.

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The Role of Vertical Shear on Aviation Turbulence within Cirrus Bands of a Simulated Western Pacific Cyclone

Monthly Weather Review ◽

10.1175/mwr-d-14-00008.1 ◽

2014 ◽

Vol 142 (8) ◽

pp. 2794-2813 ◽

Cited By ~ 24

Author(s):

Jung-Hoon Kim ◽

Hye-Yeong Chun ◽

Robert D. Sharman ◽

Stanley B. Trier

Keyword(s):

Vertical Wind Shear ◽

Vertical Shear ◽

Cloud Base ◽

Weather Research And Forecasting ◽

Cube Root ◽

Commercial Aircraft ◽

Severe Intensity ◽

Unstable Layer ◽

Generation Mechanisms

Abstract At 0300 UTC 9 September 2010, commercial aircraft traveling between Tokyo and Hawaii encountered regions of moderate and severe intensity turbulence at about 12-km elevation in or just above banded structures in the cirrus anvil associated with an oceanic cyclone located off the east coast of Japan. The generation mechanisms of the cirrus bands and turbulence are investigated using the Advanced Research Weather Research and Forecasting Model with five nested domains having a finest horizontal grid spacing of 370 m. The simulation reproduces the satellite-observed patterns of cloud brightness, including the bands, and suggests that synoptic-scale vertical shear within the anvil cloud layer and radiative effects, including longwave cooling at cloud top and warming at cloud base, act together to produce banded structures within the southern edge of the cirrus cloud shield. The character of the bands within the nearly neutral or convectively unstable layer of the cirrus shield is similar to boundary layer rolls in that the vertical wind shear vectors are nearly parallel to the cirrus bands. The strong vertical shear aligned with the banded convection leads to flow deformations and mixing near the cloud top, resulting in localized moderate and severe turbulence. The estimated maximum value of the cube root of eddy dissipation rate within the bands is ~0.7 m2/3 s−1, consistent with severe turbulence levels experienced by large aircraft.

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