scholarly journals The Role of Eyewall Turbulent Transport in the Pathway to Intensification of Tropical Cyclones

2021 ◽  
Author(s):  
Ping Zhu ◽  
Andrew Hazelton ◽  
Zhan Zhang ◽  
Frank Marks ◽  
Vijay Tallapragada
Keyword(s):  
Tropical Cyclones ◽  
Turbulent Transport

scholarly journals Turbulent transport of energy across a forest and a semi-arid shrubland

2017 ◽  
Author(s):  
Tirtha Banerjee ◽  
Peter Brugger ◽  
Frederik De Roo ◽  
Konstantin Kröniger ◽  
Dan Yakir ◽  
...  
Keyword(s):  
Boundary Layer ◽  
Turbulent Transport ◽  
Longitudinal Velocity ◽  
Atmospheric Stability ◽  
Surface Heterogeneity ◽  
Flux Divergence ◽  
Diurnal Cycles ◽  
Turbulent Statistics ◽  
Semi Arid

Abstract. The role of secondary circulations has recently been studied in the context of well defined surface heterogeneity in a semi-arid ecosystem where it was found that energy balance closure over a desert-forest system and the structure of the boundary layer was impacted by advection and flux divergence. As a part of the CliFF (Climate Feedbacks and benefits of semi-arid forests, a collaboration between KIT, Germany and the Weizmann Institute, Israel) campaign, we studied the boundary layer dynamics and turbulent transport of energy corresponding to this effect in the Yatir forest situated in the Negev desert in Israel. The forest surrounded by small shrubs presents a distinct feature of surface heterogeneity, allowing us to study the differences between their interactions with the atmosphere above by conducting measurements with two EC stations and two Doppler LiDARs. As expected, the turbulence intensity and vertical fluxes of momentum and sensible heat are found to be higher above the forest compared to the shrubland. Turbulent statistics indicative of nonlocal motions are also found to differ over the forest and shrubland and also display a strong diurnal cycle. The production of turbulent kinetic energy (TKE) over the forest is strongly mechanical, while buoyancy effects generate most of the TKE over the shrubland. Overall TKE production is much higher above the forest compared to the shrubland. The forest is also found to be more efficient in dissipating TKE. The TKE budget appears to be balanced on average both for the forest and shrubland, although the imbalance of the TKE budget, which contains the role of TKE transport, is found to be quite different in terms of their variation with atmospheric stability and diurnal cycles for the forest and shrubland. The effect of very large mesoscale motions is also directly quantified following a recent formulation by Banerjee and Katul, 2013, using the measured longitudinal velocity variances and boundary layer heights. The difference of turbulent quantities and the relationships between the components of TKE budget are used to infer the characteristics of turbulent transport of energy between the desert and the forest.

scholarly journals Temporal Variability in Thermally Driven Cross-Shore Exchange: The Role of Semidiurnal Tides

2018 ◽  
Vol 48 (7) ◽  
pp. 1513-1531 ◽  
Author(s):  
Hugo N. Ulloa ◽  
Kristen A. Davis ◽  
Stephen G. Monismith ◽  
Geno Pawlak
Keyword(s):  
Temporal Variability ◽  
Dynamic Balance ◽  
Turbulent Transport ◽  
Tidal Flow ◽  
Momentum Balance ◽  
Direct Role ◽  
Thermally Driven ◽  
The Cross ◽  
Tidally Driven

AbstractWe examine temporal variability of thermally driven baroclinic cross-shore exchange in the context of a tropical fringing reef system focusing on the role of tidally driven alongshore flow. Ensemble diurnal phase averaging of cross-shore flow at the Kilo Nalu Observatory (KNO) in Oahu, Hawaii, shows a robust diurnal signal associated with an unsteady buoyancy/diffusive dynamic balance, although significant variability is observed at subdiurnal time scales. In particular, persistent fortnightly variability in the cross-shore diurnal flow pattern is consistent with modulation by the semidiurnal alongshore tidal flow. The alongshore flow plays a direct role in the cross-shore exchange momentum balance via Coriolis acceleration but also affects the cross-shore circulation indirectly via its influence on vertical turbulent diffusion. An idealized linear theoretical model for thermally driven cross-shore flow is formulated using the long-term time-averaged diurnal dynamic balance at KNO as a baseline. The model is driven at leading order by the surface heat flux, with contributions from the alongshore flow and cross-shore wind appearing as linear perturbations. Superposition of the idealized solutions for Coriolis and time-varying eddy viscosity perturbations are able to reproduce key aspects of the fortnightly variability. Modifying the model to consider a more realistic alongshore flow and considering effects of nightly convection lead to further improvements in comparisons with KNO observations. The ability of the theoretical approach to reproduce the fortnightly patterns indicates that semidiurnal variations in the alongshore flow are effective in modulating the cross-shore flow via Coriolis and vertical turbulent transport mechanisms.

scholarly journals Intense Precipitation Events Associated with Landfalling Tropical Cyclones in Response to a Warmer Climate and Increased CO2

2014 ◽  
Vol 27 (12) ◽  
pp. 4642-4654 ◽  
Author(s):  
Enrico Scoccimarro ◽  
Silvio Gualdi ◽  
Gabriele Villarini ◽  
Gabriel A. Vecchi ◽  
Ming Zhao ◽  
...  
Keyword(s):  
Tropical Cyclones ◽  
Atmospheric Carbon Dioxide ◽  
Sea Surface ◽  
Special Focus ◽  
Relative Role ◽  
Rainfall Events ◽  
Landfalling Tropical Cyclones ◽  
Precipitation Changes ◽  
Precipitation Events

Abstract In this work the authors investigate possible changes in the intensity of rainfall events associated with tropical cyclones (TCs) under idealized forcing scenarios, including a uniformly warmer climate, with a special focus on landfalling storms. A new set of experiments designed within the U.S. Climate Variability and Predictability (CLIVAR) Hurricane Working Group allows disentangling the relative role of changes in atmospheric carbon dioxide from that played by sea surface temperature (SST) in changing the amount of precipitation associated with TCs in a warmer world. Compared to the present-day simulation, an increase in TC precipitation was found under the scenarios involving SST increases. On the other hand, in a CO2-doubling-only scenario, the changes in TC rainfall are small and it was found that, on average, TC rainfall tends to decrease compared to the present-day climate. The results of this study highlight the contribution of landfalling TCs to the projected increase in the precipitation changes affecting the tropical coastal regions.

Role of Vertical Resolution in Numerical Models Towards the Intensification, Structure and Track of Tropical Cyclones

2010 ◽  
Vol 33 (4) ◽  
pp. 338-355 ◽  
Author(s):  
D. V. Bhaskar Rao ◽  
D. Hari Prasad ◽  
D. Srinivas ◽  
Y. Anjaneyulu
Keyword(s):  
Tropical Cyclones ◽  
Numerical Models ◽  
Vertical Resolution

Turbulent flow normal to a triangular cylinder

1997 ◽  
Vol 331 ◽  
pp. 107-125 ◽  
Author(s):  
D. K. HEIST ◽  
F. C. GOULDIN
Keyword(s):  
Energy Balance ◽  
Kinetic Energy ◽  
Turbulent Kinetic Energy ◽  
High Speed ◽  
Turbulent Transport ◽  
Low Frequency ◽  
Recirculation Region ◽  
Constant Density ◽  
Energy Balances

Laser Doppler Velocimetry (LDV) measurements are presented for a nominally two-dimensional constant-density flow over a surface-mounted triangular cylinder. The thickness of the boundary layer approaching the triangular cylinder is much less than the height of the triangle. Momentum and turbulent kinetic energy balances are presented and comparisons are made with other separated and reattaching flows. Also, time domain information is presented in the form of autocorrelations and spectra. From the energy balances, the importance of the pressure transport term at the high-speed edge of the shear layer is seen. Observations of the relationships between the shapes of the spectra and the details of the energy balance are made. For example, the slope of the velocity spectra varies from the free-stream value of −5/3 to a value of −1 in the middle of the recirculation region. Concurrent with this increase in slope is a decrease in the role of shear production in the turbulent kinetic energy balance and an increase in the role of advection and turbulent transport. From the two-component LDV measurements, a very low-frequency unsteadiness is shown to contribute energy preferentially to different components of the velocity fluctuations depending on the location in the flow.

scholarly journals Implications of Nonlocal Transport and Conditionally Averaged Statistics on Monin–Obukhov Similarity Theory and Townsend’s Attached Eddy Hypothesis

2018 ◽  
Vol 75 (10) ◽  
pp. 3403-3431 ◽  
Author(s):  
Qi Li ◽  
Pierre Gentine ◽  
Juan Pedro Mellado ◽  
Kaighin A. McColl
Keyword(s):  
Similarity Theory ◽  
Turbulent Transport ◽  
Strong Interactions ◽  
Similarity Function ◽  
Convective Boundary ◽  
Structure Detection ◽  
Large Eddy ◽  
Attached Eddies ◽  
The Impact

According to Townsend’s hypothesis, so-called wall-attached eddies are the main contributors to turbulent transport in the atmospheric surface layer (ASL). This is also one of the main assumptions of Monin–Obukhov similarity theory (MOST). However, previous evidence seems to indicate that outer-scale eddies can impact the ASL, resulting in deviations from the classic MOST scaling. We conduct large-eddy simulations and direct numerical simulations of a dry convective boundary layer to investigate the impact of coherent structures on the ASL. A height-dependent passive tracer enables coherent structure detection and conditional analysis based on updrafts and subsidence. The MOST similarity functions computed from the simulation results indicate a larger deviation of the momentum similarity function ϕ m from classical scaling relationships compared to the temperature similarity function ϕ h. The conditional-averaged ϕ m for updrafts and subsidence are similar, indicating strong interactions between the inner and outer layers. However, ϕ h conditioned on subsidence follows the mixed-layer scaling, while its updraft counterpart is well predicted by MOST. Updrafts are the dominant contributors to the transport of momentum and temperature. Subsidence, which comprises eddies that originate from the outer layer, contributes increasingly to the transport of temperature with increasing instability. However, u′ of different signs are distributed symmetrically in subsidence unlike the predominantly negative θ′ as instability increases. Thus, the spatial patterns of u′ w′ differ compared to θ′ w′ in regions of subsidence. These results depict the mechanisms for departure from the MOST scaling, which is related to the stronger role of subsidence.

The Role of WISHE in the Rapid Intensification of Tropical Cyclones

2020 ◽  
Vol 77 (9) ◽  
pp. 3139-3160
Author(s):  
Chieh-Jen Cheng ◽  
Chun-Chieh Wu
Keyword(s):  
Tropical Cyclones ◽  
Potential Temperature ◽  
Surface Heat ◽  
Surface Fluxes ◽  
Heat Fluxes ◽  
Rapid Intensification ◽  
Surface Heat Fluxes ◽  
Peak Intensity ◽  
Before And After

Abstract This study examines the role of surface heat fluxes, particularly in relation to the wind-induced surface heat exchange (WISHE) mechanism, in the rapid intensification (RI) of tropical cyclones (TCs). Sensitivity experiments with capped surface fluxes and thus reduced WISHE exhibit delayed RI and weaker peak intensity, while WISHE could affect the evolutions of TCs both before and after the onset of RI. Before RI, more WISHE leads to faster increase of equivalent potential temperature in the lower levels, resulting in more active and stronger convection. In addition, TCs in experiments with more WISHE reach a certain strength earlier, before the onset of RI. During the RI period, more surface heat fluxes could provide convective instability in the lower levels, and cause a consequent development in the convective activity. More efficient intensification in a TC is found with higher surface heat fluxes and larger inertial stability, leading to a stronger peak intensity, more significant and deeper warm core in TC center, and the axisymmetrization of convection in the higher levels. In both stages, different levels of WISHE alter the thermodynamic environment and convective-scale processes. In all, this study supports the crucial role of WISHE in affecting TC intensification rate for TCs with RI.

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