scholarly journals The Outer-Core Wind Structure of Tropical Cyclones

2018 ◽  
Vol 96 (4) ◽  
pp. 297-315 ◽  
Author(s):  
Kelvin T. F. CHAN ◽  
Johnny C. L. CHAN
Keyword(s):  
Tropical Cyclones ◽  
Outer Core ◽  
Wind Structure

scholarly journals Size and Strength of Tropical Cyclones as Inferred from QuikSCAT Data

2012 ◽  
Vol 140 (3) ◽  
pp. 811-824 ◽  
Author(s):  
Kelvin T. F. Chan ◽  
Johnny C. L. Chan
Keyword(s):  
Tropical Cyclones ◽  
High Strength ◽  
Outer Core ◽  
The North ◽  
Large Size ◽  
Tangential Wind ◽  
Ocean Surface Winds ◽  
Mean Size ◽  
The Mean ◽  
Potential Factors

A comprehensive statistical climatology of the size and strength of the tropical cyclones (TCs) occurring over the western North Pacific (WNP; including the South China Sea) and the North Atlantic (NA; including the Gulf of Mexico and the Caribbean Sea) between 1999 and 2009 is constructed based on Quick Scatterometer (QuikSCAT) data. The size and strength of a TC are defined, respectively, as the azimuthally averaged radius of 17 m s−1 of ocean-surface winds (R17) and the azimuthally averaged tangential wind within 1°–2.5°-latitude radius from the TC center (outer-core wind strength, OCS). The mean TC size and strength are found to be 2.13° latitude and 19.6 m s−1, respectively, in the WNP, and 1.83° latitude and 18.7 m s−1 in the NA. While the correlation between size and strength is strong (r ≈ 0.9), that between intensity and either size or strength is weak. Seasonally, midsummer (July) and late-season (October) TCs are significantly larger in the WNP, while the mean size is largest in September in the NA. The percentage frequency of TCs having large size or high strength is also found to vary spatially and seasonally. In addition, the interannual variation of TC size and strength in the WNP correlate significantly with the TC lifetimes and the effect of El Niño over the WNP. TC lifetime and seasonal subtropical ridge activities are shown to be potential factors that affect TC size and strength.

scholarly journals Horizontal Transition of Turbulent Cascade in the Near-Surface Layer of Tropical Cyclones

2015 ◽  
Vol 72 (12) ◽  
pp. 4915-4925 ◽  
Author(s):  
Jie Tang ◽  
David Byrne ◽  
Jun A. Zhang ◽  
Yuan Wang ◽  
Xiao-tu Lei ◽  
...  
Keyword(s):  
Surface Layer ◽  
Tropical Cyclones ◽  
Inner Core ◽  
Outer Core ◽  
Core Region ◽  
Near Surface ◽  
Sources And Sinks ◽  
Available Energy ◽  
Energy Transportation ◽  
Turbulent Cascade

Abstract Tropical cyclones (TC) consist of a large range of interacting scales from hundreds of kilometers to a few meters. The energy transportation among these different scales—that is, from smaller to larger scales (upscale) or vice versa (downscale)—may have profound impacts on TC energy dynamics as a result of the associated changes in available energy sources and sinks. From multilayer tower measurements in the low-level (<120 m) boundary layer of several landing TCs, the authors found there are two distinct regions where the energy flux changes from upscale to downscale as a function of distance to the storm center. The boundary between these two regions is approximately 1.5 times the radius of maximum wind. Two-dimensional turbulence (upscale cascade) occurs more typically at regions close to the inner-core region of TCs, while 3D turbulence (downscale cascade) mostly occurs at the outer-core region in the surface layer.

scholarly journals A Latent Heat Retrieval and Its Effects on the Intensity and Structure Change of Hurricane Guillermo (1997). Part II: Numerical Simulations

2012 ◽  
Vol 69 (11) ◽  
pp. 3128-3146 ◽  
Author(s):  
Stephen R. Guimond ◽  
Jon M. Reisner
Keyword(s):  
Numerical Simulations ◽  
Tropical Cyclones ◽  
Latent Heat ◽  
Inner Core ◽  
Doppler Radar ◽  
Model Parameters ◽  
Saturation State ◽  
Wind Structure ◽  
Tangential Wind ◽  
Airborne Doppler Radar

Abstract In Part I of this study, a new algorithm for retrieving the latent heat field in tropical cyclones from airborne Doppler radar was presented and fields from rapidly intensifying Hurricane Guillermo (1997) were shown. In Part II, the usefulness and relative accuracy of the retrievals is assessed by inserting the heating into realistic numerical simulations at 2-km resolution and comparing the generated wind structure to the radar analyses of Guillermo. Results show that using the latent heat retrievals as forcing produces very low intensity and structure errors (in terms of tangential wind speed errors and explained wind variance) and significantly improves simulations relative to a predictive run that is highly calibrated to the latent heat retrievals by using an ensemble Kalman filter procedure to estimate values of key model parameters. Releasing all the heating/cooling in the latent heat retrieval results in a simulation with a large positive bias in Guillermo’s intensity that motivates the need to determine the saturation state in the hurricane inner-core retrieval through a procedure similar to that described in Part I of this study. The heating retrievals accomplish high-quality structure statistics by forcing asymmetries in the wind field with the generally correct amplitude, placement, and timing. In contrast, the latent heating fields generated in the predictive simulation contain a significant bias toward large values and are concentrated in bands (rather than discrete cells) stretched around the vortex. The Doppler radar–based latent heat retrievals presented in this series of papers should prove useful for convection initialization and data assimilation to reduce errors in numerical simulations of tropical cyclones.

Examining asymmetric outer-core CAPE in sheared tropical cyclones based on the FNL data set

2021 ◽  
Author(s):  
Yufan Dai ◽  
Qingqing Li ◽  
Lijuan Wang ◽  
Hong Chen
Keyword(s):  
Tropical Cyclones ◽  
Outer Core ◽  
Data Set

Predicting Hurricane Intensity and Structure Changes Associated with Eyewall Replacement Cycles

2012 ◽  
Vol 27 (2) ◽  
pp. 484-488 ◽  
Author(s):  
James P. Kossin ◽  
Matthew Sitkowski
Keyword(s):  
Tropical Cyclones ◽  
Statistical Models ◽  
Hurricane Intensity ◽  
Environmental Features ◽  
Wind Structure ◽  
Structure Changes ◽  
Additional Challenge ◽  
Eyewall Replacement Cycles ◽  
Operational Guidance ◽  
Storm Cloud

Abstract Eyewall replacement cycles are commonly observed in tropical cyclones and are well known to cause fluctuations in intensity and wind structure. These fluctuations are often large and rapid and pose a significant additional challenge to intensity forecasting, yet there is presently no objective operational guidance available to forecasters that targets, quantifies, and predicts these fluctuations. Here the authors introduce new statistical models that are based on a recently documented climatology of intensity and structure changes associated with eyewall replacement cycles in Atlantic Ocean hurricanes. The model input comprises environmental features and satellite-derived features that contain information on storm cloud structure. The models predict the amplitude and timing of the intensity fluctuations, as well as the fluctuations of the wind structure, and can provide real-time operational objective guidance to forecasters.

scholarly journals Airborne Doppler Observations of the Inner-Core Structural Differences between Intensifying and Steady-State Tropical Cyclones

2013 ◽  
Vol 141 (9) ◽  
pp. 2970-2991 ◽  
Author(s):  
Robert Rogers ◽  
Paul Reasor ◽  
Sylvie Lorsolo
Keyword(s):  
Steady State ◽  
Tropical Cyclones ◽  
Vertical Velocity ◽  
Mass Flux ◽  
Inner Core ◽  
Outer Core ◽  
Intensity Increase ◽  
Velocity Spectrum ◽  
Convective Bursts ◽  
Flux Profile

Abstract Differences in the inner-core structure of intensifying [IN; intensity increase of at least 20 kt (24 h)−1, where 1 kt = 0.51 m s−1] and steady-state [SS; intensity remaining between ±10 kt (24 h)−1] tropical cyclones (TCs) are examined using composites of airborne Doppler observations collected from NOAA P-3 aircraft missions. The IN dataset contains 40 eyewall passes from 14 separate missions, while the SS dataset contains 53 eyewall passes from 14 separate missions. Intensifying TCs have a ringlike vorticity structure inside the radius of maximum wind (RMW); lower vorticity in the outer core; a deeper, stronger inflow layer; and stronger axisymmetric eyewall upward motion compared with steady-state TCs. There is little difference in the vortex tilt between 2 and 7 km, and both IN and SS TCs show an eyewall precipitation and updraft asymmetry whose maxima are located in the downshear and downshear-left region. The azimuthal coverage of eyewall and outer-core precipitation is greater for IN TCs. There is little difference in the distribution of downdrafts and weak to moderate updrafts in the eyewall. The primary difference is seen at the high end of the vertical velocity spectrum, where IN TCs have a larger number of convective bursts. These bursts accomplish more vertical mass flux, but they compose such a small portion of the total vertical velocity distribution that there is little difference in the shape of the net mass flux profile. The radial location of convective bursts for IN TCs is preferentially located inside the RMW, where the axisymmetric vorticity is generally higher, whereas for SS TCs the bursts are located outside the RMW.

scholarly journals A direct aircraft observation of helical rolls in the tropical cyclone boundary layer

2021 ◽  
Vol 11 (1) ◽  
Author(s):  
Jie Tang ◽  
Jun A. Zhang ◽  
Pakwai Chan ◽  
Kaikwong Hon ◽  
Xiaotu Lei ◽  
...  
Keyword(s):  
Boundary Layer ◽  
Tropical Cyclone ◽  
Tropical Cyclones ◽  
Numerical Models ◽  
Correlation Method ◽  
Outer Core ◽  
Eddy Correlation ◽  
Turbulence Structure ◽  
Planetary Boundary Layer Parameterization ◽  
Tropical Cyclone Boundary Layer

AbstractHelical rolls are known to play a significant role in modulating both the mean and turbulence structure of the atmospheric boundary layer in tropical cyclones. However, in-situ measurements of these rolls have been limited due to safety restrictions. This study presents analyses of data collected by an aircraft operated by the Hong Kong Observatory in Typhoon Kalmaegi (1415) and Typhoon Nida (1604). Examination of the flight-level data at ~ 600 m altitude confirmed the existence of sub-kilometer-scale rolls. These rolls were mostly observed in the outer-core region. Turbulent momentum fluxes were computed using the eddy correlation method. The averaged momentum flux of flight legs with rolls was found to be ~ 2.5 times that of legs without rolls at a similar wind speed range. This result suggests that rolls could significantly modulate turbulent transfer in the tropical cyclone boundary layer. This roll effect on turbulent fluxes should be considered in the planetary boundary layer parameterization schemes of numerical models simulating and forecasting tropical cyclones.

scholarly journals Extensive High-Resolution Synthetic Aperture Radar (SAR) Data Analysis of Tropical Cyclones: Comparisons with SFMR Flights and Best Track

2020 ◽  
Vol 148 (11) ◽  
pp. 4545-4563 ◽  
Author(s):  
Clement Combot ◽  
Alexis Mouche ◽  
John Knaff ◽  
Yili Zhao ◽  
Yuan Zhao ◽  
...  
Keyword(s):  
High Resolution ◽  
Synthetic Aperture Radar ◽  
Tropical Cyclones ◽  
Surface Wind ◽  
Heavy Precipitation ◽  
Ocean Surface ◽  
Outer Core ◽  
Synthetic Aperture ◽  
Airborne Measurements ◽  
Aperture Radar

AbstractTo produce more precise descriptions of air–sea exchanges under tropical cyclones (TCs), spaceborne synthetic aperture radar (SAR) instruments provide unique capabilities to probe the ocean surface conditions, at very high spatial resolution, and on synoptic scales. Using highly resolved (3 km) wind fields, an extensive database is constructed from RadarSat-2 and Sentinel-1 SAR acquisitions. Spanning 161 tropical cyclones, the database covers all TC intensity categories that have occurred in 5 different TC basins, and include 29 cases coincident with SFMR measurements. After locating the TC center, a specific methodology is applied to filter out areas contaminated by heavy precipitation to help extract, for each acquisition, the maximum wind speed (Vmax), its associated radius (Rmax), and corresponding outer wind radii (R34/50/64 kt). These parameters are then systematically compared with best track (BTK), and when available, SFMR airborne measurements. For collocated SFMR and SAR observations, comparisons yield root-mean-squares of 3.86 m s−1 and 3 km for ocean surface wind speeds and TC Rmax, respectively. High correlations remain for category-5 cases, with Vmax exceeding 60 m s−1. The largest discrepancies are found between BTK and SAR Rmax estimates, with Rmax fluctuations poorly captured by BTK, especially for rapidly evolving category-3, -4, and -5 TCs. In heavy precipitation (>35 mm h−1), the SAR C-band measurements may be impacted, with local ambiguities associated with rain features, as revealed by external rain measurements. Still, this large dataset demonstrates that SAR measurements have unique high-resolution capabilities, capturing the inner- and outer-core radial structure of the TC vortex, and provide independent and complementary measurements than those used for BTK estimates.

scholarly journals Outer Rainbands–Driven Secondary Eyewall Formation of Tropical Cyclones

2020 ◽  
Vol 77 (6) ◽  
pp. 2217-2236
Author(s):  
Yi-Fan Wang ◽  
Zhe-Min Tan
Keyword(s):  
Boundary Layer ◽  
Tropical Cyclones ◽  
Positive Feedback ◽  
Outer Core ◽  
Relative Vorticity ◽  
Wind Maximum ◽  
Formation Pathway ◽  
Physical Conditions ◽  
Secondary Eyewall Formation ◽  
Tangential Wind

Abstract Secondary eyewall formation (SEF) could be considered as the aggregation of a convective-ring coupling with a tangential wind maximum outside the primary eyewall of a tropical cyclone (TC). The dynamics of SEF are investigated using idealized simulations based on a set of triplet experiments, whose differences are only in the initial outer-core wind speed. The triplet experiments indicate that the unbalanced boundary layer (BL) process driven by outer rainbands (ORBs) is essential for the canonical SEF. The developments of a secondary tangential wind maximum and a secondary convective ring are governed by two different pathways, which are well coupled in the canonical SEF. Compared with inner/suppressed rainbands, the downwind stratiform sectors of ORBs drive significant stronger BL convergence at its radially inward side, which fastens up the SEF region and links the two pathways. In the wind-maximum formation pathway, the positive feedback among the BL convergence, supergradient force, and relative vorticity within the BL dominates the spinup of a secondary tangential wind maximum. In the convective-ring formation pathway, the BL convergence contributes to the ascending motion through the frictional-forced updraft and accelerated outflow associated with the supergradient force above the BL. Driven only by inner rainbands, the simulated vortex develops a fake SEF with only the secondary convective ring since the rainband-driven BL convergence is less enhanced and thus fails to maintain the BL positive feedback in the wind-maximum pathway. Therefore, only ORBs can promote the canonical SEF. It also infers that any environmental/physical conditions favorable for the development of ORBs will ultimately contribute to SEF.

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