scholarly journals Effects of Tropospheric Vertical Wind Shear on Gravity Waves Generated by Tropical Cyclones

2019 ◽  
Vol 46 (8) ◽  
pp. 4523-4530 ◽  
Author(s):  
Yuan Wang ◽  
Lifeng Zhang ◽  
Yun Zhang ◽  
Jiping Guan
Keyword(s):  
Tropical Cyclones ◽  
Gravity Waves ◽  
Wind Shear ◽  
Vertical Wind Shear ◽  
Vertical Wind

scholarly journals The Unexpected Rapid Intensification of Tropical Cyclones in Moderate Vertical Wind Shear. Part I: Overview and Observations

2018 ◽  
Vol 146 (11) ◽  
pp. 3773-3800 ◽  
Author(s):  
David R. Ryglicki ◽  
Joshua H. Cossuth ◽  
Daniel Hodyss ◽  
James D. Doyle
Keyword(s):  
Tropical Cyclones ◽  
Wind Shear ◽  
Vertical Wind Shear ◽  
Convective Cloud ◽  
Vertical Wind ◽  
Rapid Intensification ◽  
Brightness Temperatures ◽  
Idealized Modeling ◽  
Hurricane Prediction ◽  
Upper Level

Abstract A satellite-based investigation is performed of a class of tropical cyclones (TCs) that unexpectedly undergo rapid intensification (RI) in moderate vertical wind shear between 5 and 10 m s−1 calculated as 200–850-hPa shear. This study makes use of both infrared (IR; 11 μm) and water vapor (WV; 6.5 μm) geostationary satellite data, the Statistical Hurricane Prediction Intensity System (SHIPS), and model reanalyses to highlight commonalities of the six TCs. The commonalities serve as predictive guides for forecasters and common features that can be used to constrain and verify idealized modeling studies. Each of the TCs exhibits a convective cloud structure that is identified as a tilt-modulated convective asymmetry (TCA). These TCAs share similar shapes, upshear-relative positions, and IR cloud-top temperatures (below −70°C). They pulse over the core of the TC with a periodicity of between 4 and 8 h. Using WV satellite imagery, two additional features identified are asymmetric warming/drying upshear of the TC relative to downshear, as well as radially thin arc-shaped clouds on the upshear side. The WV brightness temperatures of these arcs are between −40° and −60°C. All of the TCs are sheared by upper-level anticyclones, which limits the strongest environmental winds to near the tropopause.

Impact of Vertical Wind Shear on Gravity Wave Propagation in the Land–Sea-Breeze Circulation at the Equator

2019 ◽  
Vol 76 (10) ◽  
pp. 3247-3265
Author(s):  
Yu Du ◽  
Richard Rotunno ◽  
Fuqing Zhang
Keyword(s):  
Gravity Wave ◽  
Gravity Waves ◽  
Wind Shear ◽  
Vertical Wind Shear ◽  
Sea Breeze ◽  
Vertical Wind ◽  
Background Wind ◽  
Breeze Circulation ◽  
Attenuation Level ◽  
Ray Path

Abstract The impact of vertical wind shear on the land–sea-breeze circulation at the equator is explored using idealized 2D numerical simulations and a simple 2D linear analytical model. Both the idealized and linear analytical models indicate Doppler shifting and attenuation effects coexist under the effect of vertical wind shear for the propagation of gravity waves that characterize the land–sea-breeze circulation. Without a background wind, the idealized sea breeze has two ray paths of gravity waves that extend outward and upward from the coast. A uniform background wind causes a tilting of the two ray paths due to Doppler shifting. With vertical shear in the background wind, the downstream ray path of wave propagation can be rapidly attenuated near a certain level, whereas the upstream ray path is not attenuated and the amplitudes even increase with height. The downstream attenuation level is found to descend with increasing linear wind shear. The present analytical model establishes that the attenuation level corresponds to the critical level where the background wind is equal to the horizontal gravity wave phase speed. The upstream gravity wave ray path can propagate upward without attenuation as there is no critical level there.

scholarly journals Rainfall Mechanisms for One of the Wettest Tropical Cyclones on Record in Australia—Oswald (2013)

2020 ◽  
Vol 148 (6) ◽  
pp. 2503-2525
Author(s):  
Difei Deng ◽  
Elizabeth A. Ritchie
Keyword(s):  
Tropical Cyclones ◽  
Wind Shear ◽  
Heavy Rainfall ◽  
Large Scale ◽  
Vertical Wind Shear ◽  
Monsoon Trough ◽  
Vertical Wind ◽  
Lower Latitude ◽  
Cape York ◽  
Frictional Convergence

Abstract Tropical Cyclone Oswald (2013) is considered to be one of the highest-impact storms to make landfall in northern Australia even though it only reached a maximum category 1 intensity on the Australian category scale. After making landfall on the west coast of Cape York Peninsula, Oswald turned southward, and persisted for more than 7 days moving parallel to the coastline as far south as 30°S. As one of the wettest tropical cyclones (TCs) in Australian history, the favorable configurations of a lower-latitude active monsoon trough and two consecutive midlatitude trough–jet systems generally contributed to the maintenance of the Oswald circulation over land and prolonged rainfall. As a result, Oswald produced widespread heavy rainfall along the east coast with three maximum centers near Weipa, Townsville, and Rockhampton, respectively. Using high-resolution WRF simulations, the mechanisms associated with TC Oswald’s rainfall are analyzed. The results show that the rainfall involved different rainfall mechanisms at each stage. The land–sea surface friction contrast, the vertical wind shear, and monsoon trough were mostly responsible for the intensity and location for the first heavy rainfall center on the Cape York Peninsula. The second torrential rainfall near Townsville was primarily a result of the local topography and land–sea frictional convergence in a conditionally unstable monsoonal environment with frictional convergence due to TC motion modulating some offshore rainfall. The third rainfall area was largely dominated by persistent high vertical wind shear forcing, favorable large-scale quasigeostrophic dynamic lifting from two midlatitude trough–jet systems, and mesoscale frontogenesis lifting.

scholarly journals Further examination of the thermodynamic modification of the inflow layer of tropical cyclones by vertical wind shear

2013 ◽  
Vol 13 (1) ◽  
pp. 327-346 ◽  
Author(s):  
M. Riemer ◽  
M. T. Montgomery ◽  
M. E. Nicholls
Keyword(s):  
Tropical Cyclones ◽  
Wind Shear ◽  
Numerical Experiments ◽  
Structural Changes ◽  
Potential Temperature ◽  
Vertical Wind Shear ◽  
Vertical Wind ◽  
Experimental Setup ◽  
Power Machine ◽  
The Impact

Abstract. Recent work has developed a new framework for the impact of vertical wind shear on the intensity evolution of tropical cyclones. A focus of this framework is on the frustration of the tropical cyclone's power machine by shear-induced, persistent downdrafts that flush relatively cool and dry (lower equivalent potential temperature, θe) air into the storm's inflow layer. These previous results have been based on idealised numerical experiments for which we have deliberately chosen a simple set of physical parameterisations. Before efforts are undertaken to test the proposed framework with real atmospheric data, we assess here the robustness of our previous results in a more realistic and representative experimental setup by surveying and diagnosing five additional numerical experiments. The modifications of the experimental setup comprise the values of the exchange coefficients of surface heat and momentum fluxes, the inclusion of experiments with ice microphysics, and the consideration of weaker, but still mature tropical cyclones. In all experiments, the depression of the inflow layer θe values is significant and all tropical cyclones exhibit the same general structural changes when interacting with the imposed vertical wind shear. Tropical cyclones in which strong downdrafts occur more frequently exhibit a more pronounced depression of inflow layer θe outside of the eyewall in our experiments. The magnitude of the θe depression underneath the eyewall early after shear is imposed in our experiments correlates well with the magnitude of the ensuing weakening of the respective tropical cyclone. Based on the evidence presented, it is concluded that the newly proposed framework is a robust description of intensity modification in our suite of experiments.

scholarly journals A new paradigm for intensity modification of tropical cyclones: thermodynamic impact of vertical wind shear on the inflow layer

2009 ◽  
Vol 9 (3) ◽  
pp. 10711-10775 ◽  
Author(s):  
M. Riemer ◽  
M. T. Montgomery ◽  
M. E. Nicholls
Keyword(s):  
Boundary Layer ◽  
Tropical Cyclones ◽  
Wind Shear ◽  
Vertical Wind Shear ◽  
Vertical Wind ◽  
Vertical Shear ◽  
Carnot Cycle ◽  
Close Link ◽  
Storm Intensity ◽  
Intensity Evolution

Abstract. An important roadblock to improved intensity forecasts for tropical cyclones (TCs) is our incomplete understanding of the interaction of a TC with the environmental flow. In this paper we re-visit the classical idealised numerical experiment of tropical cyclones (TCs) in vertical wind shear on an f-plane. We employ a set of simplified model physics – a simple bulk aerodynamic boundary layer scheme and "warm rain" microphysics – to foster better understanding of the dynamics and thermodynamics that govern the modification of TC intensity. A suite of experiments is performed with intense TCs in moderate to strong vertical shear. In all experiments the TC is resilient to shear but significant differences in the intensity evolution occur. The ventilation of the TC core with dry environmental air at mid-levels and the dilution of the upper-level warm core are two prevailing hypotheses for the adverse effect of vertical shear on storm intensity. Here we propose an alternative and arguably more effective mechanism how cooler and drier (lower θe) air – "anti-fuel" for the TC power machine – can enter the core region of the TC. Strong and persistent downdrafts flux low θe air from the lower and middle troposphere into the boundary layer, significantly depressing the θe values in the storm's inflow layer. Air with lower θe values enters the eyewall updrafts, considerably reducing eyewall θe values in the azimuthal mean. When viewed from the perspective of an idealised Carnot-cycle heat engine a decrease of storm intensity can thus be expected. Although the Carnot cycle model is – if at all – only valid for stationary and axisymmetric TCs, a strong correlation between the downward transport of low θe into the boundary layer and the intensity evolution offers further evidence in support of our hypothesis. The downdrafts that flush the inflow layer with low θe air are associated with a quasi-stationary region of convective activity outside the TC's eyewall. We show evidence that, to zero order, the formation of the convective asymmetry is driven by the balanced dynamical response of the TC vortex to the vertical shear forcing. Thus a close link is provided between the thermodynamic impact in the near-core boundary layer and the balanced dynamics governing the TC vortex evolution.

scholarly journals The Unexpected Rapid Intensification of Tropical Cyclones in Moderate Vertical Wind Shear. Part II: Vortex Tilt

2018 ◽  
Vol 146 (11) ◽  
pp. 3801-3825 ◽  
Author(s):  
David R. Ryglicki ◽  
James D. Doyle ◽  
Yi Jin ◽  
Daniel Hodyss ◽  
Joshua H. Cossuth
Keyword(s):  
Tropical Cyclones ◽  
Wind Shear ◽  
Deep Convection ◽  
Vertical Wind Shear ◽  
Vertical Wind ◽  
Rapid Intensification ◽  
Model Simulations ◽  
Observational Analysis ◽  
Idealized Model ◽  
Cold Anomaly

Abstract We investigate a class of tropical cyclones (TCs) that undergo rapid intensification (RI) in moderate vertical wind shear through analysis of a series of idealized model simulations. Two key findings derived from observational analysis are that the average 200–850-hPa shear value is 7.5 m s−1 and that the TCs displayed coherent cloud structures, deemed tilt-modulated convective asymmetries (TCA), which feature pulses of deep convection with periods of between 4 and 8 h. Additionally, all of the TCs are embedded in an environment that is characterized by shear associated with anticyclones, a factor that limits depth of the strongest environmental winds in the vertical. The idealized TC develops in the presence of relatively shallow environmental wind shear of an anticyclone. An analysis of the TC tilt in the vertical demonstrates that the source of the observed 4–8-h periodicity of the TCAs can be explained by smaller-scale nutations of the tilt on the longer, slower upshear precession. When the environmental wind shear occurs over a deeper layer similar to that of a trough, the TC does not develop. The TCAs are characterized as collections of updrafts that are buoyant throughout the depth of the TC since they rise into a cold anomaly caused by the tilting vortex. At 90 h into the simulation, RI occurs, and the tilt nutations (and hence the TCAs) cease to occur.

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