scholarly journals The interaction between cold fronts and convection in the mid-latitudes

2021 ◽  
Author(s):  
George Pacey ◽  
Stephan Pfahl ◽  
Lisa Schielicke
Keyword(s):  
Diurnal Cycle ◽  
Cell Tracking ◽  
Cold Front ◽  
Heavy Rain ◽  
Convective Cell ◽  
Detection Methods ◽  
Cold Fronts ◽  
Forcing Mechanisms ◽  
Convective Cells ◽  
Frontal Boundary

<p>Cold fronts provide an environment favourable for convective initiation in the mid-latitudes. Some studies also show the presence of a cold front can increase the chance of certain convective hazards, such as hail and heavy rain. Convection initiates in three locations in respect to cold fronts: <em>ahead</em> of the cold front in the warm sector of the cyclone, directly <em>at</em> the cold frontal boundary and also <em>behind</em> the cold front. Previous literature has typically focused on each initiation location independently, thus a comprehensive study investigating the link between cold fronts and convection is currently lacking from literature. This study seeks to better understand the climatology, scale interactions and forcing mechanisms of convection at each initiation location relative to the front (i.e., behind, at, ahead).</p><p>Automatic front detection methods are applied to reanalysis data and a convective cell-tracking dataset from the German Weather Service is used to build a climatology of cold fronts and convection between April–September. Convective cells are found to initiate most commonly 200–300km ahead of the cold front during late afternoon. Cells behind the front primarily initiate in north-western Germany and exhibit a strong diurnal cycle. On the contrary, cells at and ahead of the front initiate most frequently in southern Germany and exhibit a less prominent diurnal cycle, especially for cells at the frontal boundary. Lightning probability decreases with closing proximity to the cold front and the average number of cell initiations per day is significantly higher on days with cold fronts opposed to days without. The next stages of research will investigate the relative importance of various forcing mechanisms on the development of convective cells at different cell-front positions.</p>

scholarly journals Observational Analysis of the 27 May 1997 Central Texas Tornadic Event. Part II: Tornadoes

2007 ◽  
Vol 135 (3) ◽  
pp. 727-735 ◽  
Author(s):  
Adam L. Houston ◽  
Robert B. Wilhelmson
Keyword(s):  
Boundary Layer ◽  
Observational Study ◽  
Cold Front ◽  
Convective Cell ◽  
Horizontal Shear ◽  
Low Level ◽  
Central Texas ◽  
Low Levels ◽  
Convective Cells ◽  
Gust Front

Abstract The 27 May 1997 central Texas tornadic event has been investigated in a two-part observational study. As demonstrated in Part I, the 1D environment associated with this event was unfavorable for significant (≥F2) tornadoes. Yet, the storm complex produced at least six significant tornadoes, including one rated F5 (the Jarrell, Texas, tornado). The purpose of this article is to examine the spatiotemporal interrelationships between tornadoes, preexisting boundaries, antecedent low-level mesocyclones, convective cells, and midlevel mesocyclones. It is shown that each of the six observed tornadoes that produced greater than F0 damage formed along the storm-generated gust front, not along preexisting boundaries. Half of these tornadoes formed on the distorted gust front, the portion of the storm-generated gust front whose orientation was deformed largely by the horizontal shear across the cold front. The remaining three tornadoes developed at the gust front cusp (the persistent gust front inflection located at the northeast end of the gust front distortion). Unlike the tornadoes south of the gust front cusp, these tornadoes are found to be associated with antecedent mesocyclones located in the low levels above the boundary layer. Furthermore, these mesocyclonic tornadoes are found to be larger and more destructive than the three nonmesocyclonic tornadoes. The formation of the Jarrell tornado is found to occur as a nearly stationary convective cell became collocated with a south-southwestward-moving low-level mesocyclone near the gust front cusp—a behavior that resembles the formation of nonsupercell tornadoes. It is argued that the back-building propagation/maintenance of the storm complex enabled this juxtaposition of convective cells with vorticity along the distorted gust front and may have therefore enabled tornado formation. Each of the convective cells without midlevel mesocyclones was found to remain farther from the boundaries than the mesocyclonic cells. Since the cells nearest to the boundaries were longer lived than the remaining cells, it is argued that cells near the boundaries were mesocyclonic because the boundaries yielded cells that were more likely to support temporally coherent midlevel rotation.

scholarly journals Environment and morphology of mesoscale convective systems associated with the Changma front during 9–10 July 2007

2012 ◽  
Vol 30 (8) ◽  
pp. 1235-1248 ◽  
Author(s):  
J.-H. Jeong ◽  
D.-I. Lee ◽  
C.-C. Wang ◽  
S.-M. Jang ◽  
C.-H. You ◽  
...  
Keyword(s):  
Cold Front ◽  
Low Pressure ◽  
Convective Cell ◽  
Mesoscale Convective Systems ◽  
Low Level ◽  
Convective Systems ◽  
Warm Front ◽  
Synoptic Conditions ◽  
Mesoscale Convective ◽  
Convective Cells

Abstract. To understand the different environment and morphology for heavy rainfall during 9–10 July 2007, over the Korean Peninsula, mesoscale convective systems (MCSs) that accompanied the Changma front in two different regions were investigated. The sub-synoptic conditions were analysed using mesoscale analysis data (MANAL), reanalysis data, weather charts and Multi-functional Transport Satellite (MTSAT-IR) data. Dual-Doppler radar observations were used to analyse the wind fields within the precipitation systems. During both the case periods, the surface low-pressure field intensified and moved northeastward along the Changma front. A low-level warm front gradually formed with an east-west orientation, and the cold front near the low pressure was aligned from northeast to southwest. The northern convective systems (meso-α-scale) were embedded within an area of stratiform cloud north of the warm front. The development of low-level pressure resulted in horizontal and vertical wind shear due to cyclonic circulation. The wind direction was apparently different across the warm front. In addition, the southeasterly flow (below 4 km) played an important role in generating new convective cells behind the prevailing convective cell. Each isolated southern convective cell (meso-β-scale) moved along the line ahead of the cold front within the prefrontal warm sector. These convective cells developed when a strong southwesterly low-level jet (LLJ) intensified and moisture was deeply advected into the sloping frontal zone. A high equivalent potential temperature region transported warm moist air in a strong southwesterly flow, where the convectively unstable air led to updraft and downdraft with a strong reflectivity core.

scholarly journals Comparison of Radar-Based Hail Detection Using Single- and Dual-Polarization

2019 ◽  
Vol 11 (12) ◽  
pp. 1436 ◽  
Author(s):  
Skripniková ◽  
Řezáčová
Keyword(s):  
Comparative Analysis ◽  
Heavy Rain ◽  
Radar Data ◽  
Severe Weather ◽  
Detection Methods ◽  
Polarimetric Radar ◽  
Dual Polarization ◽  
Rain Events ◽  
Single Polarization ◽  
Strong Agreement

The comparative analysis of radar-based hail detection methods presented here, uses C-band polarimetric radar data from Czech territory for 5 stormy days in May and June 2016. The 27 hail events were selected from hail reports of the European Severe Weather Database (ESWD) along with 21 heavy rain events. The hail detection results compared in this study were obtained using a criterion, which is based on single-polarization radar data and a technique, which uses dual-polarization radar data. Both techniques successfully detected large hail events in a similar way and showed a strong agreement. The hail detection, as applied to heavy rain events, indicated a weak enhancement of the number of false detected hail pixels via the dual-polarization hydrometeor classification. We also examined the performance of hail size detection from radar data using both single- and dual-polarization methods. Both the methods recognized events with large hail but could not select the reported events with maximum hail size (diameter above 4 cm).

scholarly journals A CloudSat–CALIPSO View of Cloud and Precipitation Properties across Cold Fronts over the Global Oceans

2015 ◽  
Vol 28 (17) ◽  
pp. 6743-6762 ◽  
Author(s):  
Catherine M. Naud ◽  
Derek J. Posselt ◽  
Susan C. van den Heever
Keyword(s):  
Large Scale ◽  
Cold Front ◽  
Conveyor Belt ◽  
Low Level ◽  
Scale Parameters ◽  
Convective Clouds ◽  
Cold Fronts ◽  
Surface Front ◽  
High Level ◽  
The Impact

Abstract The distribution of cloud and precipitation properties across oceanic extratropical cyclone cold fronts is examined using four years of combined CloudSat radar and CALIPSO lidar retrievals. The global annual mean cloud and precipitation distributions show that low-level clouds are ubiquitous in the postfrontal zone while higher-level cloud frequency and precipitation peak in the warm sector along the surface front. Increases in temperature and moisture within the cold front region are associated with larger high-level but lower mid-/low-level cloud frequencies and precipitation decreases in the cold sector. This behavior seems to be related to a shift from stratiform to convective clouds and precipitation. Stronger ascent in the warm conveyor belt tends to enhance cloudiness and precipitation across the cold front. A strong temperature contrast between the warm and cold sectors also encourages greater post-cold-frontal cloud occurrence. While the seasonal contrasts in environmental temperature, moisture, and ascent strength are enough to explain most of the variations in cloud and precipitation across cold fronts in both hemispheres, they do not fully explain the differences between Northern and Southern Hemisphere cold fronts. These differences are better explained when the impact of the contrast in temperature across the cold front is also considered. In addition, these large-scale parameters do not explain the relatively large frequency in springtime postfrontal precipitation.

scholarly journals An Empirical Perspective on Cold Fronts

2008 ◽  
Vol 55 ◽  
pp. 97-108
Author(s):  
Edwin Kessler
Keyword(s):  
Boundary Layer ◽  
Local Temperature ◽  
Cold Fronts ◽  
Empirical Perspective ◽  
Frontal Boundary

Abstract Oklahoma Mesonetwork data are used to illustrate important atmospheric features that are not well shown by the usual synoptic data. For example, some shifts of wind from south to north that are shown as cold fronts on synoptic charts are not cold fronts by any plausible definition. As previously discussed by Fred Sanders and others, such errors in analysis can be reduced by knowledge of the wide variety of weather phenomena that actually exists, and by more attention to temperatures at the earth's surface as revealed by conventional synoptic data. Mesoscale data for four cases reinforce previous discussions of the ephemeral nature of fronts and deficiencies in the usual analyses of cold fronts. One type of misanalyzed case involves post-cold-frontal boundary layer air that is warmer than the prefrontal air. A second type is usually nocturnal, with a rise of local temperature during disruption of an inversion and a wind shift with later cooling that accompanies advection of a climatological gradient of temperature.

scholarly journals Contrasting Hydrodynamic Responses to Atmospheric Systems with Different Scales: Impact of Cold Fronts vs. That of a Hurricane

2020 ◽  
Vol 8 (12) ◽  
pp. 979
Author(s):  
Wei Huang ◽  
Chunyan Li
Keyword(s):  
Water Level ◽  
Cold Front ◽  
Volume Transport ◽  
Water Volume ◽  
Cold Fronts ◽  
Barataria Bay ◽  
Before And After ◽  
Frequent Exchange ◽  
The Right ◽  
Mexico Coast

In this paper, subtidal responses of Barataria Bay to an atmospheric cold front in 2014 and Hurricane Barry of 2019 are studied. The cold fronts had shorter influencing periods (1 to 3 days), while Hurricane Barry had a much longer influencing period (about 1 week). Wind direction usually changes from southern quadrants to northern quadrants before and after a cold front’s passage. For a hurricane making its landfall at the norther Gulf of Mexico coast, wind variation is dependent on the location relative to the location of landfall. Consequently, water level usually reaches a trough after the maximum cold front wind usually; while after the maximum wind during a hurricane, water level mostly has a surge, especially on the right-hand side of the hurricane. Water level variation induced by Hurricane Barry is about 3 times of that induced by a cold front event. Water volume flux also shows differences under these two weather types: the volume transport during Hurricane Barry was 4 times of that during a cold front. On the other hand, cold front events are much more frequent (30–40 times a year), and they lead to more frequent exchange between Barataria Bay and the coastal ocean.

scholarly journals The Origin of Western European Warm-Season Prefrontal Convergence Lines

2016 ◽  
Vol 31 (5) ◽  
pp. 1417-1431 ◽  
Author(s):  
Johannes M. L. Dahl ◽  
Jannick Fischer
Keyword(s):  
Western Europe ◽  
Cold Front ◽  
Warm Season ◽  
Surface Velocity ◽  
Weather Research And Forecasting ◽  
Forecasting Model ◽  
Cold Fronts ◽  
Convergence Line ◽  
Ageostrophic Circulation ◽  
Q Vector

Abstract The authors investigate the origin of prefrontal, warm-season convergence lines over western Europe using the Weather Research and Forecasting Model. These lines form east of the cold front in the warm sector of an extratropical cyclone, and they are frequently the focus for convective development. It is shown that these lines are related to a low-level thermal ridge that accompanies the base of an elevated mixed layer (EML) plume generated over the Iberian Peninsula and northern Africa. Using Q-vector diagnostics, including the components that describe scalar and rotational quasigeostrophic frontogenesis, it is shown that the convergence line is associated with the rearrangement of the isentropes especially at the western periphery of the EML plume. The ascending branch of the resulting ageostrophic circulation coincides with the surface velocity convergence. The modeling results are supported by a 3-yr composite analysis of cold fronts with and without preceding convergence lines using NCEP–NCAR Reanalysis-1 data.

Convective cell and Alfvén vortices in an inhomogeneous rotating cold magnetoplasma

1987 ◽  
Vol 37 (2) ◽  
pp. 199-208 ◽  
Author(s):  
P. K. Shukla ◽  
R. Bharuthram
Keyword(s):  
Nonlinear Equations ◽  
Particle Transport ◽  
Special Class ◽  
Convective Cell ◽  
Stationary Solutions ◽  
Magnetized Plasma ◽  
Alfvén Waves ◽  
Convective Cells ◽  
Shear Alfven Waves ◽  
Analytical Expressions

It is shown that double vortices are a special class of stationary solutions of the set of nonlinear equations that governs the dynamics of modified convective cells and shear Alfvén waves in a cold rotating magnetized plasma. Criteria for the existence of dipole vortices as well as several analytical expressions for the vortex profiles are presented. It is suggested that modified convective cell and Alfvén dipole vortices may cause anomalous cross-field particle transport in a low-β plasma, such as the ionosphere.

Analysis of a server convective rainstorm in the weak background

2020 ◽  
Author(s):  
zhang yingxin ◽  
qin rui
Keyword(s):  
Boundary Layer ◽  
Cloud Model ◽  
Vertical Wind Shear ◽  
Sea Breeze ◽  
Heavy Rain ◽  
High Energy ◽  
Convective Cell ◽  
Visible Image ◽  
Convergence Line ◽  
Strong Winds

<p>Using conventional and unconventional meteorological observation dataes, RMAPS-NOW( RR4DVar cloud model), the severe convective rainstorm occurred over the Beijing-Tianjin-Hebei junction area on May 17, 2019 was analyzed. Taking the observation of  Tongzhou 101 farm rainstorm (17: 30-20h precipitation 179.1mm) as an example, the results showed that this server convective rainstorm took place under a weak background, (1) Boundary conditions : The Beijing-Tianjin-Hebei area had high temperature and high humidity. The θse energy front was located in the middle of Beijing-Tianjin-Hebei. The CAPE at Beijing Observatory reached 1113 J · Kg-1 at 08h, and correction value reached 2669 J · Kg-1 at 14h. Convection cloud streets appeared around 12 o'clock in the visible image of the Himawari-8 satellite; the southeast wind jet in the boundary layer provided sufficient water  for convection development; at 20 o'clock, sounding showed that the vertical wind shear of 0-6 km increased to 17.5 m · s-1. (2) Trigger conditions: The southeast wind at the rear of the offshore High merged with sea breeze and pushed inland, formed a local convergence line with the local southerly wind in the central part of Beijing, Tianjin, and Hebei, and convection occurred at the convergence line and the θse energy front. (3) Tongzhou heavy rain was caused by two convective cells. Cell 1 was generated at the convergence line and the θse front. It developed into a server storm within 1 hour, and the composite reflectivity was > 60dBz. Subsequently, at its downstream (northwest side, the leading airflow is the southeast airflow), Cell 2 developed rapidly, and the two Celles revolved, moved over Tongzhou successively, accompanied by heavy rainfall ,hail and strong winds. (4) RMAPS-NOW data can describe the refined process of cells formation and evolution, that is, the θse field in the Beijing-Tianjin-Hebei region is extremely uneven, even in the θse front area. In the boundary layer convergence line and θse high-energy region, the convective bubble stimulated the formation of cell 1, the airflow spined up, and the development of the convective cell was strengthened. Half an hour later, a single cell was gradually separated into two cells (cell 1 and cell 2) in the upper layer, and the updraft gradually separated from the center into two rotating oblique updrafts. Seen from the echo profile, the two cells were connected by a cloud bridge and rotated clockwise. The convergence line in the boundary connected the two cells and rotated organically.</p>

Two Winter Storms Encountered by Columbus in 1493 Near the Azores*

1941 ◽  
Vol 22 (8) ◽  
pp. 303-308 ◽  
Author(s):  
Charles F. Brooks
Keyword(s):  
Cold Front ◽  
Winter Storms ◽  
Severe Storms ◽  
Cold Fronts

Synopsis The two severe storms that overtook Columbus on the return portion of his first voyage, when examined in the light of modern frontal theory, do not appear to have been simple circular storms, as previously thought, but disturbances marked by well developed fronts. The centers of both passed north of Columbus; he apparently experienced the warm sectors of both. The February storm seems to have had two cold fronts, and the March one a very sharp cold front. Storms of both kinds have been observed in the same portion of the Atlantic in recent years.

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