scholarly journals Aerosol effects on the anvil characteristics, cold pool forcing and stratiform-convective precipitation partitioning and latent heating of mesoscale convective systems

2018 ◽  
Author(s):  
Susan van den Heever
Keyword(s):  
Mesoscale Convective Systems ◽  
Convective Precipitation ◽  
Cold Pool ◽  
Latent Heating ◽  
Convective Systems ◽  
Mesoscale Convective ◽  
Aerosol Effects

Shear-Parallel Mesoscale Convective Systems in a Moist Low-Inhibition Mei-Yu Front Environment

2017 ◽  
Vol 74 (12) ◽  
pp. 4213-4228 ◽  
Author(s):  
Changhai Liu ◽  
Mitchell W. Moncrieff
Keyword(s):  
Gravity Waves ◽  
Asian Summer Monsoon ◽  
Momentum Transport ◽  
Mesoscale Convective Systems ◽  
Positive Sign ◽  
Cold Pool ◽  
Convective Systems ◽  
Mesoscale Convective ◽  
Convective Momentum Transport ◽  
Organized Convection

Abstract Numerical simulations are performed to investigate organized convection observed in the Asian summer monsoon and documented as a category of mesoscale convective systems (MCSs) over the U.S. continent during the warm season. In an idealized low-inhibition and unidirectional shear environment of the mei-yu moisture front, the structure of the simulated organized convection is distinct from that occurring in the classical quasi-two-dimensional, shear-perpendicular, and trailing stratiform (TS) MCS. Consisting of four airflow branches, a three-dimensional, eastward-propagating, downshear-tilted, shear-parallel MCS builds upshear by initiating new convection at its upstream end. The weak cold pool in the low-inhibition environment negligibly affects convection initiation, whereas convectively generated gravity waves are vital. Upstream-propagating gravity waves form a saturated or near-saturated moist tongue, and downstream-propagating waves control the initiation and growth of convection within a preexisting cloud layer. A sensitivity experiment wherein the weak cold pool is removed entirely intensifies the MCS and its interaction with the environment. The horizontal scale, rainfall rate, convective momentum transport, and transverse circulation are about double the respective value in the control simulation. The positive sign of the convective momentum transport contrasts with the negative sign for an eastward-propagating TS MCS. The structure of the simulated convective systems resembles shear-parallel organization in the intertropical convergence zone (ITCZ).

scholarly journals Near-Surface Thermodynamic Sensitivities in Simulated Extreme-Rain-Producing Mesoscale Convective Systems

2017 ◽  
Vol 145 (6) ◽  
pp. 2177-2200 ◽  
Author(s):  
Russ S. Schumacher ◽  
John M. Peters
Keyword(s):  
Water Vapor ◽  
Initial Conditions ◽  
Weather Prediction ◽  
Mesoscale Convective Systems ◽  
Cold Pool ◽  
Near Surface ◽  
Low Level ◽  
Convective Systems ◽  
Mesoscale Convective ◽  
Outflow Boundary

Abstract This study investigates the influences of low-level atmospheric water vapor on the precipitation produced by simulated warm-season midlatitude mesoscale convective systems (MCSs). In a series of semi-idealized numerical model experiments using initial conditions gleaned from composite environments from observed cases, small increases in moisture were applied to the model initial conditions over a layer either 600 m or 1 km deep. The precipitation produced by the MCS increased with larger moisture perturbations as expected, but the rainfall changes were disproportionate to the magnitude of the moisture perturbations. The experiment with the largest perturbation had a water vapor mixing ratio increase of approximately 2 g kg−1 over the lowest 1 km, corresponding to a 3.4% increase in vertically integrated water vapor, and the area-integrated MCS precipitation in this experiment increased by nearly 60% over the control. The locations of the heaviest rainfall also changed in response to differences in the strength and depth of the convectively generated cold pool. The MCSs in environments with larger initial moisture perturbations developed stronger cold pools, and the convection remained close to the outflow boundary, whereas the convective line was displaced farther behind the outflow boundary in the control and the simulations with smaller moisture perturbations. The high sensitivity of both the amount and location of MCS rainfall to small changes in low-level moisture demonstrates how small moisture errors in numerical weather prediction models may lead to large errors in their forecasts of MCS placement and behavior.

scholarly journals Sensitivity of GPS tropospheric estimates to mesoscale convective systems in West Africa

2019 ◽  
Author(s):  
Samuel Nahmani ◽  
Olivier Bock ◽  
Françoise Guichard
Keyword(s):  
West Africa ◽  
Mesoscale Convective Systems ◽  
Cold Pool ◽  
Small Scale ◽  
Strong Impact ◽  
Sampled Data ◽  
Convective Systems ◽  
Temporal Sampling ◽  
Mesoscale Convective ◽  
Convective Cells

Abstract. This study analyzes the characteristics of GPS tropospheric estimates (Zenith Wet Delays, and gradients, and post-fit phase residuals) during the passage of Mesoscale Convective Systems (MCSs) and evaluates their sensitivity to the research-level GPS data processing strategy implemented. Here, we focus on MCS events observed during the monsoon seasons of West Africa. This region is particularly well suited because of the high frequency of occurrence of MCSs in contrasting climatic environments between the Guinean coast and the Sahel. This contrast is well sampled data with the six AMMA GPS stations. Tropospheric estimates for 3-year period (2006–2008), processed with both GAMIT and GIPSY-OASIS software packages, were analyzed and inter-compared. First, the case an MCS which passed over Niamey, Niger, on 11 August 2006, demonstrates a strong impact of the MCS on GPS estimates and post-fit residuals when the GPS signals propagate through convective cells as detected on reflectivity maps from MIT’s C-band Doppler radar. The estimates are also capable of detecting changes in the structure and dynamics of the MCS. The sensitivity is however different depending on the tropospheric modeling approach adopted in the software. With GIPSY-OASIS, the high temporal sampling (5 min) of Zenith Wet Delays and gradients is well suited for detecting the small-scale, short-lived, convective cells, while the post-fit residuals remain quite small. With GAMIT, the lower temporal sampling of the estimated parameters (hourly for Zenith Wet Delays and daily for gradients) is not sufficient to capture the rapid delay variations associated with the passage of the MCS, but the post-fit phase residuals clearly reflect the presence of a strong refractivity anomaly. The results are generalized with a composite analysis of 414 MCS events observed over the 3-year period at the six GPS stations with the GIPSY-OASIS estimates. A systematic peak is found in the Zenith Wet Delays coincident with the cold-pool crossing time associated to the MCSs. The tropospheric gradients are reflecting the path of the MCS propagation (generally from East to West). This study concludes that Zenith Wet Delays, gradients, and post-fit phase residuals provide relevant and complementary information on MCSs passing over or in the vicinity of a GPS station.

scholarly journals Occurrence of Summertime Convective Precipitation and Mesoscale Convective Systems in Finland during 2000–01

2005 ◽  
Vol 133 (2) ◽  
pp. 362-373 ◽  
Author(s):  
Ari-Juhani Punkka ◽  
Marja Bister
Keyword(s):  
Deep Convection ◽  
Mesoscale Convective Systems ◽  
Convective Precipitation ◽  
Karelian Isthmus ◽  
Study Region ◽  
Convective Systems ◽  
Weather Radars ◽  
Maximum Reflectivity ◽  
Mesoscale Convective ◽  
Reflectivity Data

Abstract There are few if any studies of statistics of deep convection occurring in high-latitude regions. In this study, the basic characteristics of convective precipitation and mesoscale convective systems (MCSs) in Finland and nearby regions have been investigated by using composite reflectivity data from seven operational C-band weather radars. The period of study covered summers 2000 and 2001 from the beginning of April to the end of September. During the study period, the fraction of days with convective precipitation (with reflectivity exceeding 40 dBZ) occurring anywhere in the study region was 88%, and the fraction of days with heavy convective precipitation (with reflectivity exceeding 50 dBZ) was 61%. An MCS was defined by means of radar reflectivity as follows: a continuous area of stratiform precipitation (18–40 dBZ), with a long axis of 100 km or more in at least one direction, must exist for at least 4 h, and during the lifetime of the system the maximum reflectivity must exceed 40 dBZ during at least two consecutive hours. All precipitation features that met these criteria were considered MCSs whether they occurred in extratropical cyclones or not. An MCS was qualified as intense if the maximum reflectivity exceeded 50 dBZ during at least two consecutive hours. The total amount of MCSs observed in the study region was 341, out of which 32% were intense. Over 50% of all intense MCSs occurred in July when the majority of systems traveled along south–north- or southeast–northwest-oriented paths. For instance, in July 2001, 34 intense MCSs developed in the study region. The majority of intense systems arrived in the region of study from a channel outlined by the Sarema and the Karelian Isthmus. The average duration of all MCSs was 11.1 h with a monthly minimum of 9 h occurring in July. Generally, the intense and midsummer MCSs were clearly modulated by the diurnal heating–cooling cycle whereas the nonintense and springtime systems were less dependent on the time of the day.

scholarly journals Aerosol effects on the anvil characteristics of mesoscale convective systems

2016 ◽  
Vol 121 (18) ◽  
pp. 10,880-10,901 ◽  
Author(s):  
S. M. Saleeby ◽  
S. C. van den Heever ◽  
P. J. Marinescu ◽  
S. M. Kreidenweis ◽  
P. J. DeMott
Keyword(s):  
Mesoscale Convective Systems ◽  
Convective Systems ◽  
Mesoscale Convective ◽  
Aerosol Effects

A Lagrangian perspective on cold pool collisions

2020 ◽  
Author(s):  
Giuseppe Torri ◽  
Zhiming Kuang
Keyword(s):  
Boundary Layer ◽  
Life Cycle ◽  
Spatial Scales ◽  
Mesoscale Convective Systems ◽  
Cold Pool ◽  
Convective Systems ◽  
Cold Pools ◽  
Mesoscale Convective ◽  
Temporal And Spatial ◽  
Convective Cells

<p>Collisions represent one of the most important processes through which cold pools—essential boundary layer features of precipitating systems—help to organize convection. For example, by colliding with one another, expanding cold pools can trigger new convective cells, a process that has been argued to be important to explain the deepening of convection and the maintenance of mesoscale convective systems for many hours. In spite of their role, collisions are an understudied process, and many aspects remain to be fully clarified. In order to quantify the importance of collisions on the life cycle of cold pools, we will present some results based on a combination of numerical simulations in radiative-convective equilibrium and a Lagrangian cold pool tracking algorithm. First, we will discuss how the Lagrangian algorithm can be used to estimate that the median time of the first collision for the simulated cold pools is under 10 minutes. We will then show that cold pools are significantly deformed by collisions and lose their circular shape already at the very early stages of their life cycle. Finally, we will present results suggesting that cold pools appear to be clustered, and we will provide some estimates of the associated temporal and spatial scales.</p>

scholarly journals Sensitivity of GPS tropospheric estimates to mesoscale convective systems in West Africa

2019 ◽  
Vol 19 (14) ◽  
pp. 9541-9561 ◽  
Author(s):  
Samuel Nahmani ◽  
Olivier Bock ◽  
Françoise Guichard
Keyword(s):  
West Africa ◽  
Monsoon Season ◽  
Mesoscale Convective Systems ◽  
Cold Pool ◽  
Small Scale ◽  
Strong Impact ◽  
Convective Systems ◽  
Temporal Sampling ◽  
Mesoscale Convective ◽  
Convective Cells

Abstract. This study analyzes the characteristics of GPS tropospheric estimates (zenith wet delays – ZWDs, gradients, and post-fit phase residuals) during the passage of mesoscale convective systems (MCSs) and evaluates their sensitivity to the research-level GPS data processing strategy implemented. Here, we focus on MCS events observed during the monsoon season of West Africa. This region is particularly well suited for the study of these events due to the high frequency of MCS occurrences in the contrasting climatic environments between the Guinean coast and the Sahel. This contrast is well sampled with data generated by six African Monsoon Multidisciplinary Analysis (AMMA) GPS stations. Tropospheric estimates for a 3-year period (2006–2008), processed with both the GAMIT and GIPSY-OASIS software packages, were analyzed and intercompared. First, the case of a MCS that passed over Niamey, Niger, on 11 August 2006 demonstrates a strong impact of the MCS on GPS estimates and post-fit residuals when the GPS signals propagate through the convective cells as detected on reflectivity maps from the MIT C-band Doppler radar. The estimates are also capable of detecting changes in the structure and dynamics of the MCS. However, the sensitivity is different depending on the tropospheric modeling approach adopted in the software. With GIPSY-OASIS, the high temporal sampling (5 min) of ZWDs and gradients is well suited for detecting the small-scale, short-lived, convective cells, while the post-fit residuals remain quite small. With GAMIT, the lower temporal sampling of the estimated parameters (hourly for ZWDs and daily for gradients) is not sufficient to capture the rapid delay variations associated with the passage of the MCS, but the post-fit phase residuals clearly reflect the presence of a strong refractivity anomaly. The results are generalized with a composite analysis of 414 MCS events observed over the 3-year period at the six GPS stations with the GIPSY-OASIS estimates. A systematic peak is found in the ZWDs coincident with the cold pool crossing time associated with the MCSs. The tropospheric gradients reflect the path of the MCS propagation (generally from east to west). This study concludes that ZWDs, gradients, and post-fit phase residuals provide relevant and complementary information on MCSs passing over or in the vicinity of a GPS station.

scholarly journals Initiation and Organization Mechanisms of Mesoscale Convective Systems in a Warm-Sector Torrential Rainfall Event over Beijing

Atmosphere ◽  
2020 ◽  
Vol 11 (9) ◽  
pp. 946
Author(s):  
Lei Yin ◽  
Jiahua Mao ◽  
Fan Ping ◽  
Xiaofan Li ◽  
Ning Wang
Keyword(s):  
Mesoscale Convective Systems ◽  
Atmospheric Environment ◽  
Cold Pool ◽  
Key Factors ◽  
Convective Systems ◽  
Warm Sector ◽  
Convergence Line ◽  
Mesoscale Convective ◽  
Torrential Rainfall ◽  
Convective Cells

A torrential rainfall that occurred in Beijing during the period of 21–22 July 2012 is simulated by the Weather Research and Forecasting Model in order to investigate the probable mechanisms for the initiation and organization of warm-sector mesoscale convective systems (MCSs). The simulated results show that the cyclone, which formed in Hetao area, Inner Mongolia and moved eastward slowly, played a key role in the formation and development of warm-sector precipitation, although the favorable atmospheric environment and the configuration of weather systems are also important, which caused the trigger and organization of convective cells along Taihang Mountains. It is the interaction of the local terrain convergence line and the southerly airflows of Hetao cyclone that cause the continuous trigger of convective cells along Taihang Mountains. While, the triggers of convective cells in the plains are caused by the gravity waves, which is related to the development and eastward movement of Hetao cyclone. It must be pointed out that the merging and coupling between the cells that triggered in Taihang Mountains and moved southwesterly and the cells that triggered in plains and moved northeasterly are the key factors for the formation and development of MCSs during the warm-sector precipitation. In addition, the back-building processes and the cold pool forcing are also important for the formation and development of MCSs in this study.

scholarly journals Thermodynamic Properties of Mesoscale Convective Systems Observed during BAMEX

2008 ◽  
Vol 136 (11) ◽  
pp. 4242-4271 ◽  
Author(s):  
James Correia ◽  
Raymond W. Arritt
Keyword(s):  
Potential Temperature ◽  
Mesoscale Convective Systems ◽  
Lapse Rate ◽  
Spatiotemporal Variability ◽  
Cold Pool ◽  
Convective Systems ◽  
Stratiform Region ◽  
Bow Echo ◽  
Mesoscale Convective ◽  
Lapse Rates

Abstract Dropsonde observations from the Bow Echo and Mesoscale Convective Vortex Experiment (BAMEX) are used to document the spatiotemporal variability of temperature, moisture, and wind within mesoscale convective systems (MCSs). Onion-type sounding structures are found throughout the stratiform region of MCSs, but the temperature and moisture variability is large. Composite soundings were constructed and statistics of thermodynamic variability were generated within each subregion of the MCS. The calculated air vertical velocity helped identify subsaturated downdrafts. It was found that lapse rates within the cold pool varied markedly throughout the MCS. Layered wet-bulb potential temperature profiles seem to indicate that air within the lowest several kilometers comes from a variety of source regions. It was also found that lapse-rate transitions across the 0°C level were more common than isothermal, melting layers. The authors discuss the implications these findings have and how they can be used to validate future high-resolution numerical simulations of MCSs.

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