scholarly journals Impacts of Radiation and Cold Pools on the Intensity and Vortex Tilt of Weak Tropical Cyclones Interacting with Vertical Wind Shear

2020 ◽  
Vol 77 (2) ◽  
pp. 669-689 ◽  
Author(s):  
Rosimar Rios-Berrios
Keyword(s):  
Numerical Simulations ◽  
Tropical Cyclones ◽  
Structural Changes ◽  
Prediction Models ◽  
Weather Prediction ◽  
Vertical Wind Shear ◽  
Unexpected Finding ◽  
Cold Pools ◽  
Tropical Depressions ◽  
Microphysical Processes

Abstract Idealized numerical simulations of weak tropical cyclones (e.g., tropical depressions and tropical storms) in sheared environments indicate that vortex tilt reduction and convective symmetrization are key structural changes that can precede intensification. Through a series of ensembles of idealized numerical simulations, this study demonstrates that including radiation in the simulations affects the timing and variability of those structural changes. The underlying reason for those effects is a background thermodynamic profile with reduced energy available to fuel strong downdrafts; such a profile leads to weaker lower-tropospheric ventilation, greater azimuthal coverage of clouds and precipitation, and smaller vortex tilt with radiation. Consequently, the simulations with radiation allow for earlier intensification at stronger shear magnitudes than without radiation. An unexpected finding from this work is a reduction of both vortex tilt and intensity variability with radiation in environments with 5 m s−1 deep-layer shear. This reduction stems from reduced variability in nonlinear feedbacks between lower-tropospheric ventilation, cold pools, convection, and vortex tilt. Sensitivity experiments confirm the relationship between those processes and suggest that microphysical processes (e.g., rain evaporation) are major sources of uncertainty in the representation of weak, sheared tropical cyclones in numerical weather prediction models.

scholarly journals Long-range transport of terrain-induced turbulence from high-resolution numerical simulations

2011 ◽  
Vol 11 (22) ◽  
pp. 11793-11805 ◽  
Author(s):  
M. Katurji ◽  
S. Zhong ◽  
P. Zawar-Reza
Keyword(s):  
High Resolution ◽  
Aspect Ratio ◽  
Numerical Simulations ◽  
Long Range ◽  
Prediction Models ◽  
Atmospheric Transport ◽  
Weather Prediction ◽  
Measurement Technology ◽  
Topographic Features ◽  
Range Transport

Abstract. Over complex terrain, an important question is how various topographic features may generate or alter wind turbulence and how far the influence can be extended downstream. Current measurement technology limits the capability in providing a long-range snapshot of turbulence as atmospheric eddies travel over terrain, interact with each other, change their productive and dissipative properties, and are then observed tens of kilometers downstream of their source. In this study, we investigate through high-resolution numerical simulations the atmospheric transport of terrain-generated turbulence in an atmosphere that is neutrally stratified. The simulations are two-dimensional with an isotropic spatial resolution of 15 m and run to a quasi-steady state. They are designed in such a way to allow an examination of the effects of a bell-shaped experimental hill with varying height and aspect ratio on turbulence properties generated by another hill 20 km upstream. Averaged fields of the turbulent kinetic energy (TKE) imply that terrain could have a large influence on velocity perturbations at least 30H (H is the terrain height) upstream and downstream of the terrain, with the largest effect happening in the area of the largest pressure perturbations. The results also show that downstream of the terrain the TKE fields are sensitive to the terrain's aspect ratio with larger enhancement in turbulence by higher aspect ratio, while upstream there is a suppression of turbulence that does not appear to be sensitive to the terrain aspect ratio. Instantaneous vorticity fields shows very detailed flow structures that resemble a multitude of eddy scales dynamically interacting while shearing oppositely paired vortices. The knowledge of the turbulence production and modifications by topography from these high-resolution simulations can be helpful in understanding long-range terrain-induced turbulence and improving turbulence parameterizations used in lower resolution weather prediction models.

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 Improvement in the Forecasting of Heavy Rainfall over South China in the DSAEF_LTP Model by Introducing the Intensity of the Tropical Cyclone

2020 ◽  
Vol 35 (5) ◽  
pp. 1967-1980
Author(s):  
Ding Chenchen ◽  
Fumin Ren ◽  
Yanan Liu ◽  
John L. McBride ◽  
Tian Feng
Keyword(s):  
Tropical Cyclone ◽  
Tropical Cyclones ◽  
South China ◽  
Numerical Weather Prediction ◽  
Heavy Rainfall ◽  
Prediction Models ◽  
Weather Prediction ◽  
Numerical Weather ◽  
Landfalling Typhoon ◽  
Numerical Weather Prediction Models

AbstractThe intensity of the tropical cyclone has been introduced into the Dynamical-Statistical-Analog Ensemble Forecast (DSAEF) for Landfalling Typhoon (or tropical cyclone) Precipitation (DSAEF_LTP) model. Moreover, the accumulated precipitation prediction experiments have been conducted on 21 target tropical cyclones with daily precipitation ≥ 100 mm in South China from 2012 to 2016. The best forecasting scheme for the DSAEF_LTP model is identified, and the performance of the prediction is compared with three numerical weather prediction models (the European Centre for Medium-Range Weather Forecasts, the Global Forecast System, and T639). The forecasting ability of the DSAEF_LTP model for heavy rainfall (accumulated precipitation ≥ 250 and ≥100 mm) improves when the intensity of the tropical cyclone is introduced, giving some advantages over the three numerical weather prediction models. The selection of analog tropical cyclones with a maximum intensity (during precipitation over land) equaling to or higher than the initial intensity of the target tropical cyclone gives better forecasts. The prediction accuracy for accumulated precipitation is higher for tropical cyclones with higher intensity and higher observed precipitation, with in both cases positive linear correlations with the threat score.

An Objective Track Similarity Index and Its Preliminary Application to Predicting Precipitation of Landfalling Tropical Cyclones

2018 ◽  
Vol 33 (6) ◽  
pp. 1725-1742 ◽  
Author(s):  
Fumin Ren ◽  
Wenyu Qiu ◽  
Chenchen Ding ◽  
Xianling Jiang ◽  
Liguang Wu ◽  
...  
Keyword(s):  
Tropical Cyclones ◽  
South China ◽  
Prediction Models ◽  
Weather Prediction ◽  
Similarity Index ◽  
Precipitation Forecast ◽  
Ensemble Prediction ◽  
Track Forecast ◽  
Area Index ◽  
Landfalling Tropical Cyclones

Abstract Combining dynamical model output and statistical information in historical observations is an innovative approach to predicting severe or extreme weather. In this study, in order to examine a dynamical–statistical method for precipitation forecasting of landfalling tropical cyclones (TC), an objective TC track similarity area index (TSAI) is developed. TSAI represents an area of the enclosed scope surrounded by two TC tracks and two line segments connecting the initiating and ending points of the two tracks. The smaller the TSAI value, the greater the similarity of the two TC tracks, where a value of 0 indicates that the two tracks overlap completely. The TSAI is then preliminarily applied to a precipitation forecast test of landfalling TCs over South China. Given the considerable progress made in TC track forecasting over past few decades, TC track forecast products are also used. Through this test, a track-similarity-based landfalling TC precipitation dynamical–statistical ensemble forecast (LTP_DSEF) model is established, which consists of four steps: adopting the predicted TC track, determining the TC track similarity, checking the seasonal similarity, and making an ensemble prediction. Its application to the precipitation forecasts of landfalling TCs over South China reveals that the LTP_DSEF model is superior to three numerical weather prediction models (i.e., ECMWF, GFS, and T639/China), especially for intense precipitation at large thresholds (i.e., 100 or 250 mm) in both the training (2012–14) and independent (2015–16) samples.

scholarly journals Structural Changes Preceding Rapid Intensification in Tropical Cyclones as Shown in a Large Ensemble of Idealized Simulations

2018 ◽  
Vol 75 (2) ◽  
pp. 555-569 ◽  
Author(s):  
Yoshiaki Miyamoto ◽  
David S. Nolan
Keyword(s):  
Tropical Cyclones ◽  
Structural Changes ◽  
Deep Convection ◽  
Vertical Wind Shear ◽  
Rapid Intensification ◽  
Large Ensemble ◽  
Translation Speed ◽  
Budget Analysis ◽  
Tangential Wind ◽  
Vortex Size

Abstract Structural changes that precede rapid intensification (RI) of tropical cyclones (TCs) are examined in a full-physics model by conducting a large ensemble (270) of idealized TC simulations. The processes leading to RI in a representative case with moderate shear are consistent with previous studies for weakly sheared cases. The most distinct changes are that the vortex tilt and the vortex size begin to decrease more rapidly 6 h before the onset of RI. A vorticity budget analysis for the upper layer around the low-level center reveals that the vertical vorticity is increased by vertical advection, stretching, and tilting terms before RI, whereas the horizontal advection is small. Thus, the upright vortex structure is not achieved through a vortex alignment process but rather is built upward by deep convection. The ensemble simulations are generated by changing the intensity and size of the initial vortex, the magnitude of vertical wind shear, and the translation speed. The ensemble members that show RI are consistent with the control case and many previous studies: before the onset of RI, the intensity gradually increases, the radius of maximum tangential wind (RMW) decreases, the flow structure becomes more symmetric, the vortex tilt decreases, and the radius of maximum convergence approaches the radius of maximum winds. A dimensionless parameter representing a tendency for the formation of the vertically upright structure is considered. The product of this parameter and the local Rossby number is significantly larger for TCs that exhibit RI in the next 24 h.

scholarly journals On the Relationship of Cold Pool and Bulk Shear Magnitudes on Upscale Convective Growth in the Great Plains of the United States

Atmosphere ◽  
2021 ◽  
Vol 12 (8) ◽  
pp. 1019
Author(s):  
Zachary A. Hiris ◽  
William A. Gallus
Keyword(s):  
United States ◽  
Great Plains ◽  
Prediction Models ◽  
Weather Prediction ◽  
Vertical Wind Shear ◽  
The United States ◽  
Growth Potential ◽  
Cold Pool ◽  
Convective System ◽  
The Impact

Upscale convective growth remains a poorly understood aspect of convective evolution, and numerical weather prediction models struggle to accurately depict convective morphology. To better understand some physical mechanisms encouraging upscale growth, 30 warm-season convective events from 2016 over the United States Great Plains were simulated using the Weather Research and Forecasting (WRF) model to identify differences in upscale growth and non-upscale growth environments. Also, Bryan Cloud Model (CM1) sensitivity tests were completed using different thermodynamic environments and wind profiles to examine the impact on upscale growth. The WRF simulations indicated that cold pools are significantly stronger in cases that produce upscale convective growth within the first few hours following convective initiation compared to those without upscale growth. Conversely, vertical wind shear magnitude has no statistically significant relationship with either MCS or non-MCS events. This is further supported by the CM1 simulations, in which tests using the WRF MCS sounding developed a large convective system in all tests performed, including one which used the non-MCS kinematic profile. Likewise, the CM1 simulations of the non-upscale growth event did not produce an MCS, even when using the MCS kinematic profile. Overall, these results suggest that the near-storm and pre-convective thermodynamic environment may play a larger role than kinematics in determining upscale growth potential in the Great Plains.

scholarly journals Upper-Tropospheric Low Richardson Number in Tropical Cyclones: Sensitivity to Cyclone Intensity and the Diurnal Cycle

2016 ◽  
Vol 73 (2) ◽  
pp. 545-554 ◽  
Author(s):  
Patrick Duran ◽  
John Molinari
Keyword(s):  
Tropical Cyclones ◽  
Diurnal Cycle ◽  
Richardson Number ◽  
Vertical Wind Shear ◽  
Early Morning ◽  
Static Stability ◽  
Diurnal Variability ◽  
High Vertical Resolution ◽  
Tropical Depressions ◽  
Upper Level

Abstract High-vertical-resolution rawinsondes were used to document the existence of low–bulk Richardson number (Rb) layers in tropical cyclones. The largest frequency of low Rb existed in the inner 200 km at the 13.5-km level. This peak extended more than 1000 km from the storm center and sloped downward with radius. The presence of an extensive upper-tropospheric low-Rb layer supports the assumption of Richardson number criticality in tropical cyclone outflow by Emanuel and Rotunno. The low-Rb layers were found to be more common in hurricanes than in tropical depressions and tropical storms. This sensitivity to intensity was attributed to a reduction of upper-tropospheric static stability as tropical cyclones intensify. The causes of this destabilization include upper-level cooling that is related to an elevation of the tropopause in hurricanes and greater longwave radiative warming in the well-developed hurricane cirrus canopy. Decreased mean static stability makes the production of low Rb by gravity waves and other perturbations easier to attain. The mean static stability and vertical wind shear do not exhibit diurnal variability. There is some indication, however, that low Richardson numbers are more common in the early morning than in the early evening, especially near the 200–300-km radius. The location and timing of this diurnal variability is consistent with previous studies that found a diurnal cycle of infrared brightness temperature and rainfall in tropical cyclones.

scholarly journals The Impact of Size Sorting on the Polarimetric Radar Variables

2012 ◽  
Vol 69 (6) ◽  
pp. 2042-2060 ◽  
Author(s):  
Matthew R. Kumjian ◽  
Alexander V. Ryzhkov
Keyword(s):  
Wind Shear ◽  
Prediction Models ◽  
Weather Prediction ◽  
Vertical Wind Shear ◽  
Vertical Wind ◽  
Polarimetric Radar ◽  
Horizontal Polarization ◽  
Precipitation Regimes ◽  
Size Sorting ◽  
The Impact

Abstract Differential sedimentation of precipitation occurs because heavier hydrometeors fall faster than lighter ones. Updrafts and vertical wind shear can maintain this otherwise transient size sorting, resulting in prolonged regions of ongoing particle sorting in storms. This study quantifies the impact of size sorting on the S-band polarimetric radar variables (radar reflectivity factor at horizontal polarization ZH, differential reflectivity ZDR, specific differential phase KDP, and the copolar cross-correlation coefficient ρhv). These variables are calculated from output of two idealized bin models: a one-dimensional model of pure raindrop fallout and a two-dimensional rain shaft encountering vertical wind shear. Additionally, errors in the radar variables as simulated by single-, double-, and triple-moment bulk microphysics parameterizations are quantified for the same size sorting scenarios. Size sorting produces regions of sparsely concentrated large drops with a lack of smaller drops, causing ZDR enhancements as large as 1 dB in areas of decreased ZH, often along a ZH gradient. Such areas of enhanced ZDR are offset from those of high ZH and KDP. Illustrative examples of polarimetric radar observations in a variety of precipitation regimes demonstrate the widespread occurrence of size sorting and are consistent with the bin model simulations. Single-moment schemes are incapable of size sorting, leading to large underestimations in ZDR (>2 dB) compared to the bin model solution. Double-moment schemes with a fixed spectral shape parameter produce excessive size sorting by incorrectly increasing the number of large raindrops, overestimating ZDR by 2–3 dB. Three-moment schemes with variable shape parameters better capture the narrowing drop size distribution resulting from size sorting but can underestimate ZDR and overestimate KDP by as much as 20%. Implications for polarimetric radar data assimilation into storm-scale numerical weather prediction models are discussed.

scholarly journals Precipitation Microphysical Characteristics of Typhoon Mangkhut in Southern China Using 2D Video Disdrometers

Atmosphere ◽  
2020 ◽  
Vol 11 (9) ◽  
pp. 975
Author(s):  
Lu Feng ◽  
Sheng Hu ◽  
Xiantong Liu ◽  
Hui Xiao ◽  
Xiao Pan ◽  
...  
Keyword(s):  
Tropical Cyclones ◽  
Rain Rate ◽  
Prediction Models ◽  
Inner Core ◽  
Southern China ◽  
Weather Prediction ◽  
Liquid Water Content ◽  
Radar Reflectivity ◽  
Logarithmic Scale ◽  
China Meteorological Administration

The microphysical characteristics of tropical cyclones vary in different rain regions, which affects not only the dynamic and thermodynamic mechanisms of the typhoon system but also the development of tropical cyclones. This study analyzed the raindrop size distribution (DSD) and the gamma DSD parameters associated with Typhoon Mangkhut using three two-dimensional (2D) video disdrometers from the Longmen Field Experiment Base for Cloud Physics, China Meteorological Administration in Guangdong, China during 16–17 September 2018. According to the observed track and radar reflectivity, this process can be divided into three distinct segments: the outer rainband before landfall (S1), the inner core (S2), and the outer rainband after landfall (S3). The outer rainband mainly produces stratiform rains, while the inner core mainly produces convective rains. The temporal and spatial variations in the rain rate, radar reflectivity, and DSD parameters of the different segments were analyzed and compared at three sites. Although the DSD characteristics are distinctly different in the three segments, the DSD characteristics of the same segment were similar at different sites. In the inner core (S2), the precipitation contains smaller drops (around 0.5 mm) and the concentrations are higher within each size bin compared with those of the other segments, resulting in the maximum rain rate (11.66 mm h−1), radar reflectivity (34.53 dBZ), liquid water content (0.65 g m−3), and number concentration (4.12 mm−1 m−3 on a logarithmic scale) occurring in this segment. The Nw–Dm scatter pairs have maritime-like convection, which increases outward from the inner core (S2). The relationship between the shape (μ) and slope (Λ) was also investigated. The microphysical characteristics determined in this study provide useful information for understanding microphysical precipitation processes and for improving the precision of numerical weather prediction models.

Sign in / Sign up

Export Citation Format

Share Document