scholarly journals Kajian Quasi Linear Convective System Di Bengkulu Pada Tanggal 10 November 2017 Menggunakan Wrf-Arw

2019 ◽  
Vol 4 ◽  
pp. 15
Author(s):  
Amalia Khoirunnisa ◽  
Rizky Umul Nisa Fadillah ◽  
Marselinus Muaya ◽  
Fitria Puspita Sari
Keyword(s):  
Relative Humidity ◽  
Vertical Velocity ◽  
Convective Available Potential Energy ◽  
Cloud Fraction ◽  
Weather Research And Forecasting ◽  
Convective System ◽  
Convective Systems ◽  
Maximum Reflectivity ◽  
Arw Model ◽  
Meso Scale

<p class="AbstractEnglish"><strong>Abstract: </strong>The Quasi Linear Convective System (QLCS) is a meso-scale convective weather system that has the potential to bring heavy rains and destructive strong winds. One of the Quasi Linear Convective Systems (QLCS) that have occurred in Indonesia is the QLCS that was formed in Bengkulu on November 10, 2017. QLCS can be identified using weather radar observations through maximum reflectivity imagery that forms long lines. WRF-ARW (Weather Research and Forecasting - Advanced Research) weather modeling is able to simulate meso-scale atmospheric conditions. This study aims to examine the phenomenon of QLCS using identification of weather radar observations and the results of WRF-ARW modeling. The results showed a QLCS with a length of 82 km, began to form at 09:30 UTC and reached its peak at 10.50 UTC with a maximum reflectivity of 63 dBz. Atmospheric dynamics conditions in the form of wind / streamline patterns, vertical velocity, relative humidity, Convective Available Potential Energy (CAPE) and cloud fraction from WRF-ARW model outputs show a suitable pattern and support the occurrence of convective systems around the scene. Wind patterns at the time of the event indicate a convergence region. Meanwhile the vertical velocity value reaches a peak of 0.8 Pa / s before QLCS starts entering the mature phase. The relative humidity is 95% - 100% and the CAPE value reaches 1000 J / Kg to 1500 J / Kg. Cloud fraction in the layer near the surface reaches 1%. Verification results with observational data show that rainfall parameters produce smaller errors compared to the results of verification reflectivity values. This shows that the WRF-ARW model is still inaccurate in modeling reflectivity data.</p><p class="AbstrakIndonesia"><strong>Abstrak: </strong><em>Quasi Linear Convective System</em> (QLCS) merupakan sistem cuaca konvektif skala meso yang berpotensi membawa hujan lebat dan angin kencang yang sifatnya merusak. Salah satu <em>Quasi Linear Convective System</em> (QLCS) yang pernah terjadi di Indonesia adalah QLCS yang terbentuk di Bengkulu pada tanggal 10 November 2017. QLCS dapat diidentifikasi menggunakan pengamatan radar cuaca melalui citra <em>reflectivity</em> maksimum yang membentuk garis memanjang. Pemodelan cuaca WRF-ARW (<em>Weather Research and Forecasting </em><em>–</em><em> Advanced Research</em>) mampu mensimulasikan kondisi atmosfer skala meso. Penelitian ini bertujuan untuk mengkaji fenomena QLCS dengan menggunakan identifikasi pengamatan radar cuaca dan hasil permodelan WRF-ARW. Hasil penelitian menunjukkan QLCS dengan panjang 82 km, mulai terbentuk pada pukul 09.30 UTC dan mencapai puncaknya pada pukul 10.50 UTC dengan <em>reflectivity</em> maksimum 63 dBz. Kondisi dinamika atmosfer yang berupa pola angin/<em>streamline</em>, <em>vertical velocity</em>, kelembapan relatif,<em> Convective Available Potential Energy</em> (CAPE) dan <em>cloud fraction</em> hasil keluaran model WRF-ARW menunjukan pola yang sesuai dan mendukung terjadinya sistem konvektif di sekitar lokasi kejadian. Pola angin pada waktu kejadian menunjukan adanya daerah konvergensi. Sementara itu nilai <em>verti</em><em>c</em><em>al</em> <em>velocity</em> mencapai puncaknya 0.8 Pa/s pada saat sebelum QLCS mulai memasuki fase matang. Kelembaban relatif sebesar 95% - 100% dan nilai CAPE mencapai 1000 J/Kg hingga 1500 J/Kg. <em>Cloud fraction</em> di lapisan dekat permukaan mencapai 1 %. Hasil verifikasi dengan data observasi menunjukan parameter curah hujan menghasilkan <em>error </em>yang lebih kecil dibandingkan dengan <em>error</em> hasil verifikasi nilai <em>reflectivity</em>. Hal tersebut menunjukan bahwa model WRF-ARW masih kurang akurat dalam memodelkan data <em>reflectivity</em><em>.</em></p>

Bow Echo Sensitivity to Ambient Moisture and Cold Pool Strength

2006 ◽  
Vol 134 (3) ◽  
pp. 950-964 ◽  
Author(s):  
Richard P. James ◽  
Paul M. Markowski ◽  
J. Michael Fritsch
Keyword(s):  
Convective Available Potential Energy ◽  
Three Dimensional ◽  
Cold Pool ◽  
Convective System ◽  
Cold Air ◽  
Convective Systems ◽  
Cold Pools ◽  
Bow Echo ◽  
Dry Conditions ◽  
Water Vapor Mixing Ratio

Abstract Bow echo development within quasi-linear convective systems is investigated using a storm-scale numerical model. A strong sensitivity to the ambient water vapor mixing ratio is demonstrated. Relatively dry conditions at low and midlevels favor intense cold-air production and strong cold pool development, leading to upshear-tilted, “slab-like” convection for various magnitudes of convective available potential energy (CAPE) and low-level shear. High relative humidity in the environment tends to reduce the rate of production of cold air, leading to weak cold pools and downshear-tilted convective systems, with primarily cell-scale three-dimensionality in the convective region. At intermediate moisture contents, long-lived, coherent bowing segments are generated within the convective line. In general, the scale of the coherent three-dimensional structures increases with increasing cold pool strength. The bowing lines are characterized in their developing and mature stages by segments of the convective line measuring 15–40 km in length over which the cold pool is much stronger than at other locations along the line. The growth of bow echo structures within a linear convective system appears to depend critically on the local strengthening of the cold pool to the extent that the convection becomes locally upshear tilted. A positive feedback process is thereby initiated, allowing the intensification of the bow echo. If the environment favors an excessively strong cold pool, however, the entire line becomes uniformly upshear tilted relatively quickly, and the along-line heterogeneity of the bowing line is lost.

scholarly journals Sensitivity of Precipitation Accumulation in Elevated Convective Systems to Small Changes in Low-Level Moisture

2015 ◽  
Vol 72 (6) ◽  
pp. 2507-2524 ◽  
Author(s):  
Russ S. Schumacher
Keyword(s):  
Surface Layer ◽  
Convective Available Potential Energy ◽  
Mesoscale Convective System ◽  
Extreme Rainfall ◽  
Heavy Rain ◽  
Convective System ◽  
Modeling Framework ◽  
Near Surface ◽  
Low Level ◽  
Convective Systems

Abstract Using a method for initiating a quasi-stationary, heavy-rain-producing elevated mesoscale convective system in an idealized numerical modeling framework, a series of experiments is conducted in which a shallow layer of drier air is introduced within the near-surface stable layer. The environment is still very moist in the experiments, with changes to the column-integrated water vapor of only 0.3%–1%. The timing and general evolution of the simulated convective systems are very similar, but rainfall accumulation at the surface is changed by a much larger fraction than the reduction in moisture, with point precipitation maxima reduced by up to 29% and domain-averaged precipitation accumulations reduced by up to 15%. The differences in precipitation are partially attributed to increases in the evaporation rate in the shallow subcloud layer, though this is found to be a secondary effect. More importantly, even though the near-surface layer has strong convective inhibition in all simulations and the convective available potential energy of the most unstable parcels is unchanged, convection is less intense in the experiments with drier subcloud layers because less air originating in that layer rises in convective updrafts. An additional experiment with a cooler near-surface layer corroborates these findings. The results from these experiments suggest that convective systems assumed to be elevated are, in fact, drawing air from near the surface unless the low levels are very stable. Considering that the moisture differences imposed here are comparable to observational uncertainties in low-level temperature and moisture, the strong sensitivity of accumulated precipitation to these quantities has implications for the predictability of extreme rainfall.

scholarly journals On the Predictability of Mesoscale Convective Systems: Two-Dimensional Simulations

2008 ◽  
Vol 23 (5) ◽  
pp. 773-785 ◽  
Author(s):  
Matthew S. Wandishin ◽  
David J. Stensrud ◽  
Steven L. Mullen ◽  
Louis J. Wicker
Keyword(s):  
Wind Speed ◽  
Relative Humidity ◽  
Ensemble Member ◽  
Mesoscale Convective Systems ◽  
Convective System ◽  
Forecast Errors ◽  
Two Dimensional ◽  
Substantial Impact ◽  
Convective Systems ◽  
Mesoscale Convective

Abstract Mesoscale convective systems (MCSs) are a dominant climatological feature of the central United States and are responsible for a substantial fraction of warm season rainfall. Yet very little is known about the predictability of MCSs. To help alleviate this situation, a series of ensemble simulations of an MCS are performed on a two-dimensional, storm-scale (Δx = 1 km) model. Ensemble member perturbations in wind speed, relative humidity, and instability are based on current 24-h forecast errors from the North American Model (NAM). The ensemble results thus provide an upper bound on the predictability of mesoscale convective systems within realistic estimates of environmental uncertainty, assuming successful convective initiation. The simulations are assessed by considering an ensemble member a success when it reproduces a convective system of at least 20 km in length (roughly the size of two convective cells) within 100 km on either side of the location of the MCS in the control run. By that standard, MCSs occur roughly 70% of the time for perturbation magnitudes consistent with 24-h forecast errors. Reducing the perturbations for all fields to one-half the 24-h error values increases the MCS success rate to over 90%. The same improvement in forecast accuracy would lead to a 30%–40% reduction in maximum surface wind speed uncertainty and a roughly 20% reduction in the uncertainty in maximum updraft strength, and initially slower growth in the uncertainty in the size of the MCS. However, the occurrence of MCSs drops below 50% as the midlayer mean relative humidity falls below 65%. The response of the model to reductions in forecast errors for instability, moisture, and wind speed is not consistent and cannot be easily generalized, but each can have a substantial impact on forecast uncertainty.

scholarly journals Long-Lived Mesoscale Systems in a Low–Convective Inhibition Environment. Part II: Downshear Propagation

2015 ◽  
Vol 72 (11) ◽  
pp. 4319-4336 ◽  
Author(s):  
Mitchell W. Moncrieff ◽  
Todd P. Lane
Keyword(s):  
Convective Available Potential Energy ◽  
Mesoscale Convective System ◽  
Cold Pool ◽  
Convective System ◽  
Mesoscale Circulation ◽  
Secondary Importance ◽  
Convective Systems ◽  
Stratiform Region ◽  
Mesoscale System ◽  
Mesoscale Convective

Abstract Part II of this study of long-lived convective systems in a tropical environment focuses on forward-tilted, downshear-propagating systems that emerge spontaneously from idealized numerical simulations. These systems differ in important ways from the standard mesoscale convective system that is characterized by a rearward-tilted circulation with a trailing stratiform region, an overturning updraft, and a mesoscale downdraft. In contrast to this standard mesoscale system, the downshear-propagating system considered here does not feature a mesoscale downdraft and, although there is a cold pool it is of secondary importance to the propagation and maintenance of the system. The mesoscale downdraft is replaced by hydraulic-jump-like ascent beneath an elevated, forward-tilted overturning updraft with negligible convective available potential energy. Therefore, the mesoscale circulation is sustained almost entirely by the work done by the horizontal pressure gradient and the kinetic energy available from environmental shear. This category of organization is examined by cloud-system-resolving simulations and approximated by a nonlinear archetypal model of the quasi-steady Lagrangian-mean mesoscale circulation.

scholarly journals Study of Pre-Monsoon Thunderstorms and Associated Thermodynamic Features Over Bangladesh Using WRF-ARW Model

2019 ◽  
Vol 67 (2) ◽  
pp. 151-156
Author(s):  
Pappu Paul ◽  
Ashik Imran ◽  
Md Jafrul Islam ◽  
Alamgir Kabir ◽  
Sahadat Jaman ◽  
...  
Keyword(s):  
Relative Humidity ◽  
Potential Energy ◽  
Convective Available Potential Energy ◽  
Severe Thunderstorm ◽  
Available Potential Energy ◽  
K Index ◽  
Mesoscale System ◽  
Arw Model ◽  
Convective Inhibition ◽  
Wind Distribution

Thunderstorm is a mesoscale system (from a km to below thousands of km and sustaining less than one hour). Two pre-monsoon thunderstorms events are analyzed in this study which are named as event-1 (0030-0150 UTC of 19 April 2018 over Chattogram) and event-2 (0600-1000 UTC of 4 May 2018 over Dhaka). To predict these events Mean Convective Available Potential Energy (mCAPE), Mean Convective Inhibition Energy (mCINE), K Index (KI), Total totals Index (TTI), wind distribution, and relative humidity (RH) are investigated.The model simulated mCAPE and mCINE values, 18 hours before the events, are found greater than 1700 J/Kg and less than 100 J/Kg respectively which satisfies the conditions for thunderstorms to occur.The KI values are close to 400C and TTI values are greater or equal to 450C for both events. The wind patterns and the high value of mid –tropospheric RH also favors the formation of severe thunderstorm. Dhaka Univ. J. Sci. 67(2): 151-156, 2019 (July)

scholarly journals An Analysis of the Environments of Intense Convective Systems in West Africa in 2003

2010 ◽  
Vol 138 (10) ◽  
pp. 3721-3739 ◽  
Author(s):  
Stephen D. Nicholls ◽  
Karen I. Mohr
Keyword(s):  
West Africa ◽  
Regional Scale ◽  
Convective Available Potential Energy ◽  
Potential Temperature ◽  
Saharan Dust ◽  
Convective System ◽  
Low Level ◽  
Convective Systems ◽  
African Easterly Wave ◽  
Easterly Wave

Abstract The local- and regional-scale environments associated with intense convective systems in West Africa during 2003 were diagnosed from soundings, operational analysis, and space-based datasets. Convective system cases were identified from the Tropical Rainfall Measuring Mission (TRMM) microwave imagery and classified by the system minimum 85-GHz brightness temperature and the estimated elapsed time of propagation from terrain greater than 500 m. The speed of the midlevel jet, the magnitude of the low-level shear, and the surface equivalent potential temperature θe were greater for the intense cases compared to the nonintense cases, although the differences between the means tended to be small: less than 3 K for surface θe and less than 2 × 10−3 s−1 for low-level wind shear. Hypothesis testing of a series of commonly used intensity prediction metrics resulted in significant results only for low-level metrics such as convective available potential energy and not for any of the mid- or upper-level metrics such as the 700-hPa θe. None of the environmental variables or intensity metrics by themselves or in combination appeared to be reliable direct predictors of intensity. In the regional-scale analysis, the majority of intense convective systems occurred in the surface baroclinic zone where surface θe exceeded 344 K and the 700-hPa zonal wind speeds were less than −6 m s−1. Fewer intense cases compared to nonintense cases were associated with African easterly wave troughs. Fewer than 25% of these cases occurred in environments with detectable Saharan dust loads, and the results for intense and nonintense cases were similar. Although the discrimination between the intense and nonintense environments was narrow, the results were robust and consistent with the seasonal movement of the West African monsoon, regional differences in topography, and African easterly wave energetics.

Experiences with 0–36-h Explicit Convective Forecasts with the WRF-ARW Model

2008 ◽  
Vol 23 (3) ◽  
pp. 407-437 ◽  
Author(s):  
Morris L. Weisman ◽  
Christopher Davis ◽  
Wei Wang ◽  
Kevin W. Manning ◽  
Joseph B. Klemp
Keyword(s):  
Land Surface ◽  
Value Added ◽  
Time Frame ◽  
Convective System ◽  
Forecast Errors ◽  
Systematic Bias ◽  
Convective Systems ◽  
Mesoscale Convective ◽  
Arw Model ◽  
Pbl Scheme

Abstract Herein, a summary of the authors’ experiences with 36-h real-time explicit (4 km) convective forecasts with the Advanced Research Weather Research and Forecasting Model (WRF-ARW) during the 2003–05 spring and summer seasons is presented. These forecasts are compared to guidance obtained from the 12-km operational Eta Model, which employed convective parameterization (e.g., Betts–Miller–Janjić). The results suggest significant value added for the high-resolution forecasts in representing the convective system mode (e.g., for squall lines, bow echoes, mesoscale convective vortices) as well as in representing the diurnal convective cycle. However, no improvement could be documented in the overall guidance as to the timing and location of significant convective outbreaks. Perhaps the most notable result is the overall strong correspondence between the Eta and WRF-ARW guidance, for both good and bad forecasts, suggesting the overriding influence of larger scales of forcing on convective development in the 24–36-h time frame. Sensitivities to PBL, land surface, microphysics, and resolution failed to account for the more significant forecast errors (e.g., completely missing or erroneous convective systems), suggesting that further research is needed to document the source of such errors at these time scales. A systematic bias is also noted with the Yonsei University (YSU) PBL scheme, emphasizing the continuing need to refine and improve physics packages for application to these forecast problems.

Indirect Assimilation of Radar Reflectivity with WRF 3D-Var and Its Impact on Prediction of Four Summertime Convective Events

2013 ◽  
Vol 52 (4) ◽  
pp. 889-902 ◽  
Author(s):  
Hongli Wang ◽  
Juanzhen Sun ◽  
Shuiyong Fan ◽  
Xiang-Yu Huang
Keyword(s):  
Water Vapor ◽  
Data Assimilation ◽  
Convective Available Potential Energy ◽  
Three Dimensional ◽  
Heavy Rain ◽  
Cloud Water ◽  
Radar Reflectivity ◽  
Precipitation Forecast ◽  
Weather Research And Forecasting ◽  
Convective System

AbstractAn indirect radar reflectivity assimilation scheme has been developed within the Weather Research and Forecasting model three-dimensional data assimilation system (WRF 3D-Var). This scheme, instead of assimilating radar reflectivity directly, assimilates retrieved rainwater and estimated in-cloud water vapor. An analysis is provided to show that the assimilation of the retrieved rainwater avoids the linearization error of the Z–qr (reflectivity–rainwater) equation. A new observation operator is introduced to assimilate the estimated in-cloud water vapor. The performance of the scheme is demonstrated by assimilating reflectivity observations into the Rapid Update Cycle data assimilation and forecast system operating at Beijing Meteorology Bureau. Four heavy-rain-producing convective cases that occurred during summer 2009 in Beijing, China, are studied using the newly developed system. Results show that on average the assimilation of reflectivity significantly improves the short-term precipitation forecast skill up to 7 h. A diagnosis of the analysis fields of one case shows that the assimilation of reflectivity increases humidity, rainwater, and convective available potential energy in the convective region. As a result, the analysis successfully promotes the developments of the convective system and thus improves the subsequent prediction of the location and intensity of precipitation for this case.

scholarly journals Dynamics of Cloud-Top Generating Cells in Winter Cyclones. Part I: Idealized Simulations in the Context of Field Observations

2016 ◽  
Vol 73 (4) ◽  
pp. 1507-1527 ◽  
Author(s):  
Jason M. Keeler ◽  
Brian F. Jewett ◽  
Robert M. Rauber ◽  
Greg M. McFarquhar ◽  
Roy M. Rasmussen ◽  
...  
Keyword(s):  
Vertical Velocity ◽  
Radiative Forcing ◽  
Initial Conditions ◽  
Vertical Wind Shear ◽  
Weather Research And Forecasting ◽  
Velocity Spectrum ◽  
Latent Heating ◽  
Heating Rates ◽  
Winter Storms ◽  
Radiation Parameterizations

Abstract This paper assesses the influence of radiative forcing and latent heating on the development and maintenance of cloud-top generating cells (GCs) in high-resolution idealized Weather Research and Forecasting Model simulations with initial conditions representative of the vertical structure of a cyclone observed during the Profiling of Winter Storms campaign. Simulated GC kinematics, structure, and ice mass are shown to compare well quantitatively with Wyoming Cloud Radar, cloud probe, and other observations. Sensitivity to radiative forcing was assessed in simulations with longwave-only (nighttime), longwave-and-shortwave (daytime), and no-radiation parameterizations. The domain-averaged longwave cooling rate exceeded 0.50 K h−1 near cloud top, with maxima greater than 2.00 K h−1 atop GCs. Shortwave warming was weaker by comparison, with domain-averaged values of 0.10–0.20 K h−1 and maxima of 0.50 K h−1 atop GCs. The stabilizing influence of cloud-top shortwave warming was evident in the daytime simulation’s vertical velocity spectrum, with 1% of the updrafts in the 6.0–8.0-km layer exceeding 1.20 m s−1, compared to 1.80 m s−1 for the nighttime simulation. GCs regenerate in simulations with radiative forcing after the initial instability is released but do not persist when radiation is not parameterized, demonstrating that radiative forcing is critical to GC maintenance under the thermodynamic and vertical wind shear conditions in this cyclone. GCs are characterized by high ice supersaturation (RHice &gt; 150%) and latent heating rates frequently in excess of 2.00 K h−1 collocated with vertical velocity maxima. Ice precipitation mixing ratio maxima of greater than 0.15 g kg−1 were common within GCs in the daytime and nighttime simulations.

scholarly journals Effects of atmospheric dynamics and aerosols on the fraction of supercooled water clouds

2017 ◽  
Vol 17 (3) ◽  
pp. 1847-1863 ◽  
Author(s):  
Jiming Li ◽  
Qiaoyi Lv ◽  
Min Zhang ◽  
Tianhe Wang ◽  
Kazuaki Kawamoto ◽  
...  
Keyword(s):  
Relative Humidity ◽  
Vertical Velocity ◽  
Meteorological Parameters ◽  
Temporal Correlation ◽  
Supercooled Liquid ◽  
Satellite Observation ◽  
Static Stability ◽  
Global Scale ◽  
Atmospheric Dynamics ◽  
Horizontal Wind

Abstract. Based on 8 years of (January 2008–December 2015) cloud phase information from the GCM-Oriented Cloud-Aerosol Lidar and Infrared Pathfinder Satellite Observation (CALIPSO) Cloud Product (GOCCP), aerosol products from CALIPSO and meteorological parameters from the ERA-Interim products, the present study investigates the effects of atmospheric dynamics on the supercooled liquid cloud fraction (SCF) during nighttime under different aerosol loadings at global scale to better understand the conditions of supercooled liquid water gradually transforming to ice phase. Statistical results indicate that aerosols' effect on nucleation cannot fully explain all SCF changes, especially in those regions where aerosols' effect on nucleation is not a first-order influence (e.g., due to low ice nuclei aerosol frequency). By performing the temporal and spatial correlations between SCFs and different meteorological factors, this study presents specifically the relationship between SCF and different meteorological parameters under different aerosol loadings on a global scale. We find that the SCFs almost decrease with increasing of aerosol loading, and the SCF variation is closely related to the meteorological parameters but their temporal relationship is not stable and varies with the different regions, seasons and isotherm levels. Obviously negative temporal correlations between SCFs versus vertical velocity and relative humidity indicate that the higher vertical velocity and relative humidity the smaller SCFs. However, the patterns of temporal correlation for lower-tropospheric static stability, skin temperature and horizontal wind are relatively more complex than those of vertical velocity and humidity. For example, their close correlations are predominantly located in middle and high latitudes and vary with latitude or surface type. Although these statistical correlations have not been used to establish a certain causal relationship, our results may provide a unique point of view on the phase change of mixed-phase cloud and have potential implications for further improving the parameterization of the cloud phase and determining the climate feedbacks.

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