scholarly journals Cyclogenesis off the African Coast: The Case of Cindy in August 1999

2005 ◽  
Vol 133 (9) ◽  
pp. 2803-2813 ◽  
Author(s):  
Saïdou Moustapha Sall ◽  
Henri Sauvageot
Keyword(s):  
Tropical Cyclone ◽  
Longwave Radiation ◽  
Mesoscale Convective System ◽  
Precipitable Water ◽  
Radar Data ◽  
Vertical Shear ◽  
Convective System ◽  
Infrared Observation ◽  
African Coast ◽  
Environmental Prediction

Abstract Using radar data from Dakar (Sengal), National Centers for Environmental Prediction–National Center for Atmospheric Research (NCEP–NCAR) reanalyses, outgoing longwave radiation provided by the National Oceanic and Atmospheric Administration (NOAA) Television Infrared Observation Satellite (TIROS) satellite series as well as data from the National Hurricane Center (NHC), a cyclogenesis process leading to the birth of a tropical cyclone from a Sahelian mesoscale convective system (MCS) off the African coast of Senegal is described. The cause of this evolution seems to be the coincidence of the MCS with an easterly wave over a warm sea, the presence of a wide area of precipitable water vapor, strong convergence in the low and midtropospheric layers, and an easterly vertical shear of the zonal wind. As a result, a dynamically well organized convective system built up and the system rapidly strengthened. Before moving away from the African coast of Senegal, this perturbation, which became the tropical cyclone “Cindy,” caused the wreck of more than a hundred fishing pirogues and the deaths of many fishermen because of the suddenness and speed of the phenomenon.

Ensemble Probabilistic Prediction of a Mesoscale Convective System and Associated Polarimetric Radar Variables Using Single-Moment and Double-Moment Microphysics Schemes and EnKF Radar Data Assimilation

2017 ◽  
Vol 145 (6) ◽  
pp. 2257-2279 ◽  
Author(s):  
Bryan J. Putnam ◽  
Ming Xue ◽  
Youngsun Jung ◽  
Nathan A. Snook ◽  
Guifu Zhang
Keyword(s):  
Mesoscale Convective System ◽  
Radar Data ◽  
Convective Precipitation ◽  
Convective System ◽  
Ensemble Forecasts ◽  
Verification Methods ◽  
Probabilistic Forecasts ◽  
Mesoscale Convective ◽  
Single Moment ◽  
Double Moment

Abstract Ensemble-based probabilistic forecasts are performed for a mesoscale convective system (MCS) that occurred over Oklahoma on 8–9 May 2007, initialized from ensemble Kalman filter analyses using multinetwork radar data and different microphysics schemes. Two experiments are conducted, using either a single-moment or double-moment microphysics scheme during the 1-h-long assimilation period and in subsequent 3-h ensemble forecasts. Qualitative and quantitative verifications are performed on the ensemble forecasts, including probabilistic skill scores. The predicted dual-polarization (dual-pol) radar variables and their probabilistic forecasts are also evaluated against available dual-pol radar observations, and discussed in relation to predicted microphysical states and structures. Evaluation of predicted reflectivity (Z) fields shows that the double-moment ensemble predicts the precipitation coverage of the leading convective line and stratiform precipitation regions of the MCS with higher probabilities throughout the forecast period compared to the single-moment ensemble. In terms of the simulated differential reflectivity (ZDR) and specific differential phase (KDP) fields, the double-moment ensemble compares more realistically to the observations and better distinguishes the stratiform and convective precipitation regions. The ZDR from individual ensemble members indicates better raindrop size sorting along the leading convective line in the double-moment ensemble. Various commonly used ensemble forecast verification methods are examined for the prediction of dual-pol variables. The results demonstrate the challenges associated with verifying predicted dual-pol fields that can vary significantly in value over small distances. Several microphysics biases are noted with the help of simulated dual-pol variables, such as substantial overprediction of KDP values in the single-moment ensemble.

scholarly journals Mesoscale Features Associated with Tropical Cyclone Formations in the Western North Pacific

2008 ◽  
Vol 136 (6) ◽  
pp. 2006-2022 ◽  
Author(s):  
Cheng-Shang Lee ◽  
Kevin K. W. Cheung ◽  
Jenny S. N. Hui ◽  
Russell L. Elsberry
Keyword(s):  
Tropical Cyclone ◽  
North Pacific ◽  
Western North Pacific ◽  
Large Scale ◽  
North Pacific Ocean ◽  
Deep Convection ◽  
Mesoscale Convective System ◽  
Convective System ◽  
Synoptic Patterns ◽  
The Mean

Abstract The mesoscale features of 124 tropical cyclone formations in the western North Pacific Ocean during 1999–2004 are investigated through large-scale analyses, satellite infrared brightness temperature (TB), and Quick Scatterometer (QuikSCAT) oceanic wind data. Based on low-level wind flow and surge direction, the formation cases are classified into six synoptic patterns: easterly wave (EW), northeasterly flow (NE), coexistence of northeasterly and southwesterly flow (NE–SW), southwesterly flow (SW), monsoon confluence (MC), and monsoon shear (MS). Then the general convection characteristics and mesoscale convective system (MCS) activities associated with these formation cases are studied under this classification scheme. Convection processes in the EW cases are distinguished from the monsoon-related formations in that the convection is less deep and closer to the formation center. Five characteristic temporal evolutions of the deep convection are identified: (i) single convection event, (ii) two convection events, (iii) three convection events, (iv) gradual decrease in TB, and (v) fluctuating TB, or a slight increase in TB before formation. Although no dominant temporal evolution differentiates cases in the six synoptic patterns, evolutions ii and iii seem to be the common routes taken by the monsoon-related formations. The overall percentage of cases with MCS activity at multiple times is 63%, and in 35% of cases more than one MCS coexisted. Most of the MC and MS cases develop multiple MCSs that lead to several episodes of deep convection. These two patterns have the highest percentage of coexisting MCSs such that potential interaction between these systems may play a role in the formation process. The MCSs in the monsoon-related formations are distributed around the center, except in the NE–SW cases in which clustering of MCSs is found about 100–200 km east of the center during the 12 h before formation. On average only one MCS occurs during an EW formation, whereas the mean value is around two for the other monsoon-related patterns. Both the mean lifetime and time of first appearance of MCS in EW are much shorter than those developed in other synoptic patterns, which indicates that the overall formation evolution in the EW case is faster. Moreover, this MCS is most likely to be found within 100 km east of the center 12 h before formation. The implications of these results to internal mechanisms of tropical cyclone formation are discussed in light of other recent mesoscale studies.

Polarimetric Radar Rain Estimation through Retrieval of Drop Size Distribution Using a Bayesian Approach

2010 ◽  
Vol 49 (5) ◽  
pp. 973-990 ◽  
Author(s):  
Qing Cao ◽  
Guifu Zhang ◽  
Edward A. Brandes ◽  
Terry J. Schuur
Keyword(s):  
Bayesian Approach ◽  
Mesoscale Convective System ◽  
Radar Data ◽  
Normal Function ◽  
In Situ Measurements ◽  
Retrieval Algorithm ◽  
Convective System ◽  
Horizontal Polarization ◽  
Oklahoma Mesonet

Abstract This study proposes a Bayesian approach to retrieve raindrop size distributions (DSDs) and to estimate rainfall rates from radar reflectivity in horizontal polarization ZH and differential reflectivity ZDR. With this approach, the authors apply a constrained-gamma model with an updated constraining relation to retrieve DSD parameters. Long-term DSD measurements made in central Oklahoma by the two-dimensional video disdrometer (2DVD) are first used to construct a prior probability density function (PDF) of DSD parameters, which are estimated using truncated gamma fits to the second, fourth, and sixth moments of the distributions. The forward models of ZH and ZDR are then developed based on a T-matrix calculation of raindrop backscattering amplitude with the assumption of drop shape. The conditional PDF of ZH and ZDR is assumed to be a bivariate normal function with appropriate standard deviations. The Bayesian algorithm has a good performance according to the evaluation with simulated ZH and ZDR. The algorithm is also tested on S-band radar data for a mesoscale convective system that passed over central Oklahoma on 13 May 2005. Retrievals of rainfall rates and 1-h rain accumulations are compared with in situ measurements from one 2DVD and six Oklahoma Mesonet rain gauges, located at distances of 28–54 km from Norman, Oklahoma. Results show that the rain estimates from the retrieval agree well with the in situ measurements, demonstrating the validity of the Bayesian retrieval algorithm.

scholarly journals Toward an Understanding of Tropical Cyclone Formation with a Nonhydrostatic, Mesoscale-Convection-Resolving Model§

2013 ◽  
Vol 7 (1) ◽  
pp. 37-50
Author(s):  
Masanori Yamasaki
Keyword(s):  
Tropical Cyclone ◽  
Numerical Experiments ◽  
Vertical Shear ◽  
Initial Time ◽  
Convective System ◽  
Vortex Center ◽  
Moist Convection ◽  
Mesoscale Convection ◽  
Tropical Cyclone Formation ◽  
Convective Systems

This paper describes results from numerical experiments which have been made toward a better understanding of tropical cyclone formation. This study uses a nonhydrostatic version of the author’s mesoscale-convection-resolving model that was developed in the 1980s to improve paramerization schemes of moist convection. In this study the horizontal grid size is taken to be 20 km in an area of 6,000 km x 3,000 km, and a non-uniform coarse grid is used in two areas to its north and south. Results from two numerical experiments are presented; one (case 1) without any environmental flow, and the other (case 2) with an easterly flow without low-level vertical shear. Three circular buoyancy perturbations are placed in the west-east direction at the initial time. Convection is initiated in the imposed latently unstable (positive CAPE) area. In both cases, a vortex with a pressure low is formed, and two band-shaped convective systems are formed to the north and the south of the vortex center. The vortex and two convective systems are oriented in the westsouthwest – eastnortheast direction, and their horizontal scales are nearly 2,000 km. In case 1, the band-shaped convective system on the southern side is stronger, and winds are stronger just to its south. In contrast, in case 2, the northern convective system is stronger, and winds are stronger just to its north. Therefore, the distributions of the equivalent potential temperature in the boundary layer and latent instability (positive buoyancy of the rising air) are also quite different between cases 1 and 2. The TC formation processes in these different cases are discussed, with an emphasis on the importance of examining the time change of latent instability field.

The Analysis and Prediction of Microphysical States and Polarimetric Radar Variables in a Mesoscale Convective System Using Double-Moment Microphysics, Multinetwork Radar Data, and the Ensemble Kalman Filter

2014 ◽  
Vol 142 (1) ◽  
pp. 141-162 ◽  
Author(s):  
Bryan J. Putnam ◽  
Ming Xue ◽  
Youngsun Jung ◽  
Nathan Snook ◽  
Guifu Zhang
Keyword(s):  
Kalman Filter ◽  
Ensemble Kalman Filter ◽  
Mesoscale Convective System ◽  
Radar Data ◽  
Cold Pool ◽  
Convective System ◽  
Polarimetric Radar ◽  
Microphysics Scheme ◽  
Mesoscale Convective ◽  
Double Moment

Abstract Doppler radar data are assimilated with an ensemble Kalman Filter (EnKF) in combination with a double-moment (DM) microphysics scheme in order to improve the analysis and forecast of microphysical states and precipitation structures within a mesoscale convective system (MCS) that passed over western Oklahoma on 8–9 May 2007. Reflectivity and radial velocity data from five operational Weather Surveillance Radar-1988 Doppler (WSR-88D) S-band radars as well as four experimental Collaborative and Adaptive Sensing of the Atmosphere (CASA) X-band radars are assimilated over a 1-h period using either single-moment (SM) or DM microphysics schemes within the forecast ensemble. Three-hour deterministic forecasts are initialized from the final ensemble mean analyses using a SM or DM scheme, respectively. Polarimetric radar variables are simulated from the analyses and compared with polarimetric WSR-88D observations for verification. EnKF assimilation of radar data using a multimoment microphysics scheme for an MCS case has not previously been documented in the literature. The use of DM microphysics during data assimilation improves simulated polarimetric variables through differentiation of particle size distributions (PSDs) within the stratiform and convective regions. The DM forecast initiated from the DM analysis shows significant qualitative improvement over the assimilation and forecast using SM microphysics in terms of the location and structure of the MCS precipitation. Quantitative precipitation forecasting skills are also improved in the DM forecast. Better handling of the PSDs by the DM scheme is believed to be responsible for the improved prediction of the surface cold pool, a stronger leading convective line, and improved areal extent of stratiform precipitation.

Convection-Permitting Simulations of the Environment Supporting Widespread Turbulence within the Upper-Level Outflow of a Mesoscale Convective System

2009 ◽  
Vol 137 (6) ◽  
pp. 1972-1990 ◽  
Author(s):  
Stanley B. Trier ◽  
Robert D. Sharman
Keyword(s):  
Deep Convection ◽  
Potential Temperature ◽  
Mesoscale Convective System ◽  
Forecast Model ◽  
Static Stability ◽  
Vertical Shear ◽  
Convective System ◽  
Mesoscale Convective ◽  
Northern Edge ◽  
Upper Level

Abstract Widespread moderate turbulence was recorded on three specially equipped commercial airline flights over northern Kansas near the northern edge of the extensive cirrus anvil of a nocturnal mesoscale convective system (MCS) on 17 June 2005. A noteworthy aspect of the turbulence was its location several hundred kilometers from the active deep convection (i.e., large reflectivity) regions of the MCS. Herein, the MCS life cycle and the turbulence environment in its upper-level outflow are studied using Rapid Update Cycle (RUC) analyses and cloud-permitting simulations with the Weather Research and Forecast Model (WRF). It is demonstrated that strong vertical shear beneath the MCS outflow jet is critical to providing an environment that could support dynamic (e.g., shearing type) instabilities conducive to turbulence. Comparison of a control simulation to one in which the temperature tendency due to latent heating was eliminated indicates that strong vertical shear and corresponding reductions in the local Richardson number (Ri) to ∼0.25 at the northern edge of the anvil were almost entirely a consequence of the MCS-induced westerly outflow jet. The large vertical shear is found to decrease Ri both directly, and by contributing to reductions in static stability near the northern anvil edge through differential advection of (equivalent) potential temperature gradients, which are in turn influenced by adiabatic cooling associated with the mesoscale updraft located upstream within the anvil. On the south side of the MCS, the vertical shear associated with easterly outflow was significantly offset by environmental westerly shear, which resulted in larger Ri and less widespread model turbulent kinetic energy (TKE) than at the northern anvil edge.

scholarly journals Comparison of 3DVar and EnSRF Data Assimilation Using Radar Observations for the Analysis and Prediction of an MCS

2018 ◽  
Vol 2018 ◽  
pp. 1-18 ◽  
Author(s):  
Shibo Gao ◽  
Jinzhong Min
Keyword(s):  
Data Assimilation ◽  
Three Dimensional ◽  
Mesoscale Convective System ◽  
Final Analysis ◽  
Radar Data ◽  
Radar Reflectivity ◽  
Precipitation Forecast ◽  
Convective System ◽  
Wind Fields ◽  
Radar Observations

Using radar observations, the performances of the ensemble square root filter (EnSRF) and an indirect three-dimensional variational (3DVar) data assimilation method were compared for a mesoscale convective system (MCS) that occurred in the Front Range of the Rocky Mountains, Colorado (USA). The results showed that the root mean square innovations (RMSIs) of EnSRF were lower than 3DVar for radar reflectivity and radial velocity and that the spread of EnSRF was generally consistent with its RMSIs. EnSRF substantially improved the analysis of the MCS compared with an experiment without radar data assimilation, and it produced a slight but noticeable improvement over 3DVar in terms of both coverage and intensity. Forecast results initiated from the final analysis revealed that EnSRF generally produced the best prediction of the MCS, with improved quantitative reflectivity and precipitation forecast skills. EnSRF also demonstrated better performance than 3DVar in the prediction of neighborhood probability for reflectivity at thresholds of 20 and 35 dBZ, which better matched the observed radar reflectivity in terms of both shape and extension. Additionally, the humidity, temperature, and wind fields were also improved by EnSRF; the largest error reduction was found in the water vapor field near the surface and at upper levels.

scholarly journals Identifikasi Karakteristik Quasi-Linear Convective System Pada Maret Sampai Mei 2017 Di Wilayah Pangkalan Bun Berbasis Radar Cuaca

2019 ◽  
Vol 4 ◽  
pp. 110
Author(s):  
Meldisa Putri Maulidyah ◽  
Rossian Nursiddiq Islamiardi ◽  
Rezky Fajar Maulana ◽  
Kristian Adi Putra Tamba ◽  
Imma Redha Nugraheni ◽  
...  
Keyword(s):  
Coastal Plain ◽  
Descriptive Analysis ◽  
Mesoscale Convective System ◽  
Heavy Rain ◽  
Radar Data ◽  
Horizontal Wind ◽  
Convective System ◽  
Raw Data ◽  
Mesoscale Convective ◽  
Strong Winds

<p><strong>Abstract: </strong>Quasi Linear Convective System (QLCS) is one of the phenomena of meso-scale convective weather systems (MCS), which are linear in shape with an unspecified leftime and potentially bad weather in the form of heavy rain and strong winds. This research will identify, analyze, and characterize QLCS in the Pangkalan Bun region, Central Kalimantan, as a research location with a period of March to May 2017 using raw data radar data base of Pangkalanbun type C-Band single polarization type Selex SI Gematronik. Method of research was conducted in a descriptive analysis with a description of the QLCS temporally and spatially. The results showed the most duration was 30-60 minutes. The location of the QLCS formation is dominant in the coastal plain or lowland areas. The type of formation of QLCS is dominant broken line.</p><p><strong>Abstrak: </strong>Quasi Linear Convective System (QLCS) merupakan salah satu fenomena dari sistem cuaca konvektif skala meso atau Mesoscale Convective System (MCS) yang berbentuk linear dengan masa hidup tidak ditentukan dan berpotensi cuaca buruk berupa hujan lebat dan angin kencang. Pada penelitian ini akan mengidentifikasi, menganalisis, dan mengarakteristikan QLCS di wilayah cakupan radar Pangkalan Bun, Kalimantan Tengah sebagai lokasi penelitian dengan jangka waktu bulan Maret sampai Mei tahun 2017 menggunakan raw data radar cuaca Pangkalan Bun tipe C-Band jenis polarisasi tunggal Selex SI Gematronik. Metode yang dilakukan dalam penelitian ini adalah analisis deskriptif produk Column Max (CMAX), Combined Moment (CM), Strom Structure Analysis (SSA), Severe Weather Indicator (SWI), dan Horizontal WInd (HWIND). Hasil penelitian menunjukkan durasi pembentukan QLCS terbanyak terjadi dalam rentang 30-60 menit dengan lokasi pembentukan QLCS dominan pada area coastal plain atau dataran rendah. Tipe pembentukan QLCS dominan broken line dan banyak terjadi di pagi hari.</p>

Sign in / Sign up

Export Citation Format

Share Document