scholarly journals Sensitivity of Axisymmetric Tropical Cyclone Spinup Time to Dry Air Aloft

2016 ◽  
Vol 73 (11) ◽  
pp. 4269-4287 ◽  
Author(s):  
Brian H. Tang ◽  
Rosimar Rios-Berrios ◽  
Joshua J. Alland ◽  
Jeremy D. Berman ◽  
Kristen L. Corbosiero
Keyword(s):  
Tropical Cyclone ◽  
Kinetic Energy ◽  
Mass Flux ◽  
Deep Convection ◽  
Radial Pressure ◽  
Moisture Profile ◽  
High Entropy ◽  
Low Level ◽  
Cumulus Congestus ◽  
Moisture Profiles

Abstract The sensitivity of tropical cyclone spinup time to the initial entropy deficit of the troposphere is examined in an axisymmetric hurricane model. Larger initial entropy deficits correspond to less moisture above the initial lifting condensation level of a subcloud-layer parcel. The spinup time is quantified in terms of thresholds of integrated horizontal kinetic energy within a radius of 300 km and below a height of 1.5 km. The spinup time increases sublinearly with increasing entropy deficit, indicating the greatest sensitivity lies with initial moisture profiles closer to saturation. As the moisture profile approaches saturation, there is a large increase in the low-level, area-averaged, vertical mass flux over the spinup period because of the predominance of deep convection. Higher entropy deficit experiments have a greater amount of cumulus congestus and reduced vertical mass flux over a longer duration. Consequently, the secondary circulation takes longer to build upward, and the radial influx of angular momentum is reduced. There is also a reduction in the conversion of potential available enthalpy to horizontal kinetic energy, as a result of reduced flow down the radial pressure gradient early in the spinup period. Later in the spinup period, the low-level vortex spins up relatively quickly near the nascent radius of maximum wind in the high-entropy deficit experiments, whereas the low-level vortex spins up over a wider area in the low-entropy deficit experiments.

scholarly journals Role of Cumulus Congestus in Tropical Cyclone Formation in a High-Resolution Numerical Model Simulation

2014 ◽  
Vol 71 (5) ◽  
pp. 1681-1700 ◽  
Author(s):  
Zhuo Wang
Keyword(s):  
High Resolution ◽  
Tropical Cyclone ◽  
Deep Layer ◽  
Dominant Role ◽  
Rapid Development ◽  
Deep Convection ◽  
Cyclonic Circulation ◽  
Low Level ◽  
Cumulus Congestus

Abstract The role of cumulus congestus (shallow and congestus convection) in tropical cyclone (TC) formation is examined in a high-resolution simulation of Tropical Cyclone Fay (2008). It is found that cumulus congestus plays a dominant role in moistening the lower to middle troposphere and spinning up the near-surface circulation prior to genesis, while deep convection plays a key role in moistening the upper troposphere and intensifying the cyclonic circulation over a deep layer. The transition from the tropical wave stage to the TC stage is marked by a substantial increase in net condensation and potential vorticity generation by deep convection in the inner wave pouch region. This study suggests that TC formation can be regarded as a two-stage process. The first stage is a gradual process of moisture preconditioning and low-level spinup, in which cumulus congestus plays a dominant role. The second stage commences with the rapid development of deep convection in the inner pouch region after the air column is moistened sufficiently, whereupon the concentrated convective heating near the pouch center strengthens the transverse circulation and leads to the amplification of the cyclonic circulation over a deep layer. The rapid development of deep convection can be explained by the power-law increase of precipitation rate with column water vapor (CWV) above a critical value. The high CWV near the pouch center thus plays an important role in convective organization. It is also shown that cumulus congestus can effectively drive the low-level convergence and provides a direct and simple pathway for the development of the TC protovortex near the surface.

scholarly journals A High-Resolution Simulation of Asymmetries in Severe Southern Hemisphere Tropical Cyclone Larry (2006)

2009 ◽  
Vol 137 (12) ◽  
pp. 4171-4187 ◽  
Author(s):  
Hamish A. Ramsay ◽  
Lance M. Leslie ◽  
Jeffrey D. Kepert
Keyword(s):  
Boundary Layer ◽  
Tropical Cyclone ◽  
Southern Hemisphere ◽  
Inner Core ◽  
Mesoscale Model ◽  
Deep Convection ◽  
Vertical Motion ◽  
Vertical Shear ◽  
Low Level ◽  
Frictional Convergence

Abstract Advances in observations, theory, and modeling have revealed that inner-core asymmetries are a common feature of tropical cyclones (TCs). In this study, the inner-core asymmetries of a severe Southern Hemisphere tropical cyclone, TC Larry (2006), are investigated using the fifth-generation Pennsylvania State University–National Center for Atmospheric Research Mesoscale Model (MM5) and the Kepert–Wang boundary layer model. The MM5-simulated TC exhibited significant asymmetries in the inner-core region, including rainfall distribution, surface convergence, and low-level vertical motion. The near-core environment was characterized by very low environmental vertical shear and consequently the TC vortex had almost no vertical tilt. It was found that, prior to landfall, the rainfall asymmetry was very pronounced with precipitation maxima consistently to the right of the westward direction of motion. Persistent maxima in low-level convergence and vertical motion formed ahead of the translating TC, resulting in deep convection and associated hydrometeor maxima at about 500 hPa. The asymmetry in frictional convergence was mainly due to the storm motion at the eyewall, but was dominated by the proximity to land at larger radii. The displacement of about 30°–120° of azimuth between the surface and midlevel hydrometeor maxima is explained by the rapid cyclonic advection of hydrometeors by the tangential winds in the TC core. These results for TC Larry support earlier studies that show that frictional convergence in the boundary layer can play a significant role in determining the asymmetrical structures, particularly when the environmental vertical shear is weak or absent.

scholarly journals Impact of Stratiform Rainband Heating on the Tropical Cyclone Wind Field in Idealized Simulations

2019 ◽  
Vol 76 (8) ◽  
pp. 2443-2462 ◽  
Author(s):  
Chau-Lam Yu ◽  
Anthony C. Didlake
Keyword(s):  
Tropical Cyclone ◽  
Wind Field ◽  
Deep Convection ◽  
Cold Pool ◽  
Low Level ◽  
Secondary Eyewall Formation ◽  
Heating And Cooling ◽  
Storm Evolution ◽  
Spiral Rainbands ◽  
Diabatic Forcing

Abstract Using idealized simulations, we examine the storm-scale wind field response of a dry, hurricane-like vortex to prescribed stratiform heating profiles that mimic tropical cyclone (TC) spiral rainbands. These profiles were stationary with respect to the storm center to represent the diabatic forcing imposed by a quasi-stationary rainband complex. The first profile was typical of stratiform precipitation with heating above and cooling below the melting level. The vortex response included a mesoscale descending inflow and a midlevel tangential jet, consistent with previous studies. An additional response was an inward-spiraling low-level updraft radially inside the rainband heating. The second profile was a modified stratiform heating structure derived from observations and consisted of a diagonal dipole of heating and cooling. The same features were found with stronger magnitudes and larger vertical extents. The dynamics and implications of the forced low-level updraft were examined. This updraft was driven by buoyancy advection because of the stratiform-induced low-level cold pool. The stationary nature of the rainband diabatic forcing played an important role in modulating the required temperature and pressure anomalies to sustain this updraft. Simulations with moisture and full microphysics confirmed that this low-level updraft response was robust and capable of triggering sustained deep convection that could further impact the storm evolution, including having a potential role in secondary eyewall formation.

scholarly journals Giga-LES of Hector the Convector and Its Two Tallest Updrafts up to the Stratosphere

2016 ◽  
Vol 73 (12) ◽  
pp. 5041-5060 ◽  
Author(s):  
Thibaut Dauhut ◽  
Jean-Pierre Chaboureau ◽  
Juan Escobar ◽  
Patrick Mascart
Keyword(s):  
Deep Convection ◽  
Sea Breeze ◽  
Entrainment Rate ◽  
Tropical Tropopause Layer ◽  
Low Level ◽  
3D Objects ◽  
Eddy Simulation ◽  
Cold Pools ◽  
Tropical Tropopause ◽  
Cumulus Congestus

Abstract The dynamics of Hector the Convector, which overshot into the stratosphere on 30 November 2005 over the Tiwi Islands, Australia, is investigated using a giga-large-eddy simulation with a 100-m cubic mesh. Individual updrafts, defined as 3D objects with vertical velocity above 10 m s−1 are identified. Among the 20 000 updrafts formed during the most intense phase, only a dozen were more than 4 km tall. The two tallest updrafts accounted for more than 90% of the total vertical mass flux through the tropical tropopause layer. Their locations were determined by low-level convergence lines first created by the sea breeze in the morning, then enhanced by cold pools due to cumulus congestus. They finally reinforced each other as they moved inland and intersected. The two tallest updrafts that overshot the tropopause were contrasted with those occurring 1 h earlier and later. They presented larger widths (up to 8 km), greater buoyancy (up to 0.1 m s−2), stronger vertical velocities (up to 50 m s−1), and larger hydrometeor contents (more than 10 g kg−1). They kept their core weakly diluted on their way to the stratosphere with an entrainment rate as low as 0.08 km−1. Both the low-level convergence lines intensified by cold pools and the reduced mixing in the troposphere were found to be the determinant for the transition from deep to very deep convection.

Thermodynamic Aspects of Tropical Cyclone Formation

2012 ◽  
Vol 69 (8) ◽  
pp. 2433-2451 ◽  
Author(s):  
Zhuo Wang
Keyword(s):  
Tropical Cyclone ◽  
Deep Convection ◽  
Potential Temperature ◽  
Air Entrainment ◽  
Spatial Average ◽  
Low Level ◽  
Equivalent Potential ◽  
Thermodynamic Conditions ◽  
Short Incubation Time ◽  
Convective Organization

Abstract The thermodynamic aspects of tropical cyclone (TC) formation near the center of the wave pouch, a region of approximately closed Lagrangian circulation within the wave critical layer, are examined through diagnoses of a high-resolution numerical simulation and dropsonde data from a recent field campaign. It is found that the meso-β area near the pouch center is characterized by high saturation fraction, small difference in equivalent potential temperature θe between the surface and the middle troposphere, and a short incubation time scale. Updrafts tend to be more vigorous in this region, presumably because of reduced dry air entrainment, while downdrafts are not suppressed. The thermodynamic conditions near the pouch center are thus critically important for TC formation. The balanced responses to convective and stratiform heating at the pregenesis stage are examined using the Sawyer–Eliassen equation. Deep convection is concentrated near the pouch center. The strong radial and vertical gradients of latent heat release effectively force the transverse circulation and spin up a surface protovortex near the pouch center. Stratiform heating induces modest midlevel inflow and very weak low-level outflow, which contributes to the midlevel spinup without substantially spinning down the low-level circulation. The analysis of dropsonde data shows that the midlevel θe increases significantly near the pouch center one to two days prior to genesis but changes little away from the pouch center. This may indicate convective organization and the impending TC genesis. It also suggests that the critical information of TC genesis near the pouch center may be masked out if a spatial average is taken over the pouch scale.

Multi-scale shear impacts during the genesis of Hagupit (2008)

2020 ◽  
Author(s):  
Chaehyeon C. Nam ◽  
Michael M. Bell
Keyword(s):  
Tropical Cyclone ◽  
Doppler Radar ◽  
Negative Impact ◽  
Early Stage ◽  
Spatial Scales ◽  
Deep Convection ◽  
Vertical Wind Shear ◽  
Low Level ◽  
Multi Scale ◽  
The Impact

AbstractThe impact of vertical wind shear (VWS) on tropical cyclogenesis is examined from the synoptic to meso scales using airborne Doppler radar observations of pre-depression Hagupit during the Tropical Cyclone Structure 2008 (TCS08) / THORPEX Pacific Area Regional Campaign (T-PARC) field campaigns. The high temporal and spatial resolution observations reveal complex localized convective and vortical characteristics of a pre-depression in a sheared environment. Pre-depression Hagupit interacted with an upper-tropospheric trough during the observation period. The strong deep-layer VWS (> 20 m s−1) had a negative impact on the development through misalignment of the low and mid-level circulations and dry air intrusion. However, the low-level circulation persisted and the system ultimately formed into a tropical cyclone after it left the high-shear zone. Here we propose that a key process that enabled the pre-depression to survive through the upper-tropospheric trough interaction was persistent vorticity amplification on the meso-γ scale that was aggregated on the meso-α scale within the wave pouch. Multi-Doppler wind analysis indicates that cumulus congestus tilted the low-level horizontal vorticity into the vertical in the early stage of convective life-cycle, followed by stretching from maturing deep convection. Variations in low-level VWS on the meso-β scale affect convective organization and horizontal vorticity generation. The results provide new insights into multi-scale processes during TC genesis and the interactions of a pre-depression with VWS at various spatial scales.

Large-scale state and evolution of the atmosphere and ocean during PISTON 2018

2021 ◽  
pp. 1-59
Author(s):  
Adam H. Sobel ◽  
Janet Sprintall ◽  
Eric D. Maloney ◽  
Zane K. Martin ◽  
Shuguang Wang ◽  
...  
Keyword(s):  
Tropical Cyclone ◽  
Large Scale ◽  
Deep Convection ◽  
Intraseasonal Variability ◽  
Reanalysis Data ◽  
The Philippines ◽  
Heat Fluxes ◽  
Surface Heat Fluxes ◽  
Low Level ◽  
The North

AbstractThe Propagation of Intraseasonal Tropical Oscillations (PISTON) experiment conducted a field campaign inAugust-October 2018. The R/V Thomas G. Thompson made two cruises in thewestern North Pacific region north of Palau and east of the Philippines. Using select field observations and global observational and reanalysis data sets, this study describes the large-scale state and evolution of the atmosphere and ocean during these cruises. Intraseasonal variability was weak during the field program, except for a period of suppressed convection in October. Tropical cyclone activity, on the other hand, was strong. Variability at the ship location was characterized by periods of low-level easterly atmospheric flow with embedded westward propagating synoptic-scale atmospheric disturbances, punctuated by periods of strong low-level westerly winds that were both connected to the Asian monsoon westerlies and associated with tropical cyclones. In the most dramatic case, westerlies persisted for days during and after tropical cyclone Jebi had passed to the north of the ship. In these periods, the sea surface temperature was reduced by a couple of degrees by both wind mixing and net surface heat fluxes that were strongly (~200Wm−2) out of the ocean, due to both large latent heat flux and cloud shading associated with widespread deep convection. Underway conductivity-temperature transects showed dramatic cooling and deepening of the ocean mixed layer and erosion of the barrier layer after the passage of Typhoon Mangkhut due to entrainment of cooler water from below. Strong zonal currents observed over at least the upper 400 meters were likely related to the generation and propagation of near-inertial currents.

scholarly journals Convective damping of buoyancy anomalies and its effect on lapse rates in the tropical lower troposphere

2006 ◽  
Vol 6 (1) ◽  
pp. 1-12 ◽  
Author(s):  
I. Folkins
Keyword(s):  
Mass Flux ◽  
Deep Convection ◽  
Lower Troposphere ◽  
Anomalous Behavior ◽  
Flux Divergence ◽  
Clear Sky ◽  
Rossby Radius Of Deformation ◽  
Lapse Rates ◽  
The Tropics ◽  
Moisture Profiles

Abstract. In regions of the tropics undergoing active deep convection, the variation of lower tropospheric lapse rates (2.0 km to 5.2 km) with height is inconsistent with both reversible moist adiabatic and pseudoadiabatic assumptions. It is argued that this anomalous behavior arises from the tendency for the divergence of a convective buoyancy anomaly to be primarily offset by the collective divergence of other updrafts and downdrafts within one Rossby radius of deformation. Ordinarily, convective mass flux divergences are at least partially offset by an induced radiative mass flux divergence in the background atmosphere. If mass flux divergences from lower tropospheric convection are balanced mainly by those of neighboring updrafts/downdrafts, it would force the vertical clear sky radiative mass flux of the background atmosphere to be weakly dependent on height. This is observed at several radiosonde locations in the Western Tropical Pacific between 2.0 and the 5.2 km melting level. At tropical locations where SST's exceed 27°C over a region whose horizontal extent exceeds the local Rossby radius, this condition on the vertical variation of the background radiative mass flux partially constrains the range of physically allowed mean temperature and moisture profiles in the lower troposphere.

Precipitation Processes and Vortex Alignment during the Intensification of a Weak Tropical Cyclone in Moderate Vertical Shear

2020 ◽  
Vol 148 (5) ◽  
pp. 1899-1929 ◽  
Author(s):  
Robert F. Rogers ◽  
Paul D. Reasor ◽  
Jonathan A. Zawislak ◽  
Leon T. Nguyen
Keyword(s):  
Mass Flux ◽  
Structural Changes ◽  
Doppler Radar ◽  
Deep Convection ◽  
Vertical Wind Shear ◽  
Lower Troposphere ◽  
Cooperative Interaction ◽  
Vertical Shear ◽  
Low Level ◽  
Flux Profile

Abstract The mechanisms underlying the development of a deep, aligned vortex, and the role of convection and vertical shear in this process, are explored by examining airborne Doppler radar and deep-layer dropsonde observations of the intensification of Hurricane Hermine (2016), a long-lived tropical depression that intensified to hurricane strength in the presence of moderate vertical wind shear. During Hermine’s intensification the low-level circulation appeared to shift toward locations of deep convection that occurred primarily downshear. Hermine began to steadily intensify once a compact low-level vortex developed within a region of deep convection in close proximity to a midlevel circulation, causing vorticity to amplify in the lower troposphere primarily through stretching and tilting from the deep convection. A notable transition of the vertical mass flux profile downshear of the low-level vortex to a bottom-heavy profile also occurred at this time. The transition in the mass flux profile was associated with more widespread moderate convection and a change in the structure of the deep convection to a bottom-heavy mass flux profile, resulting in greater stretching of vorticity in the lower troposphere of the downshear environment. These structural changes in the convection were related to a moistening in the midtroposphere downshear, a stabilization in the lower troposphere, and the development of a mid- to upper-level warm anomaly associated with the developing midlevel circulation. The evolution of precipitation structure shown here suggests a multiscale cooperative interaction across the convective and mesoscale that facilitates an aligned vortex that persists beyond convective time scales, allowing Hermine to steadily intensify to hurricane strength.

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