The organization or mode of an MCS is described by variations in the convective and stratiform precipitation structure along a line or amorphous, leading, parallel, or trailing stratiform. Sometimes different modes occur as stages of an MCS lifecycle.
The structure and lifecycle of MCSs depends largely on the balance between the horizontal vorticity of the cold pool generated by convection and horizontal vorticity associated with the low to mid-tropospheric shear. For long-lasting MCSs, the stronger the Coriolis force, the more asymmetric will be their structure; a major factor in the subtropics and midlatitudes where larger rain areas form on their poleward side.
Continental MCSs are more intense than oceanic systems. In general updraft velocities over continents are times more rapid than over ocean, leading to taller clouds and deeper mixed phase cloud layer over land. Tropical squall lines MCSs or squall clusters are usually identified by a line of vigorous convective cells extending for km along its major axis e.
In the monsoon regions, squall line MCSs move both eastward and westward in response to the environmental shear environmental shear. The most commonly-observed squall line structure, in both the tropics and midlatitudes, is the leading convective line with trailing stratiform region Fig. The large cloud shield seen on satellite images, and enhanced growth of precipitation particles, results from sloping deep-layer ascent in the stratiform region of MCS.
Other features often seen in tropical and midlatitude squall lines are the bright band, due to the high reflectivity of melting ice particles, and the weak echo transition zone, due to subsidence and suppression of precipitation particle growth.
Although the three modes were identified from midlatitude systems, they are still applicable to the tropics. In prevailing easterly winds, tropical squall clusters move rapidly westward as a continuous disturbance or family of regenerating systems that undergoes decay and regeneration over several days.
Amazon squall lines occur about every two days and are most common during April to June and least frequent during October and November. Tropical squall line passage is marked by a distinct roll cloud followed by a sudden wind squall then a heavy downpour that usually lasts about half an hour. Below the melting level indicated by the bright band in Fig.
The moist static energy decreases with the passage of the leading convective line and gradually increases in the wake of the convection Fig. The lifecycle of a tropical squall line with trailing stratiform region is illustrated and described in Box Box The bow-echo is a subset of squall line MCSs. When a line of strong convective cells or a single large convective cell evolves into an arc shaped MCS, it is known as bow echo because of its bow shape on radar displays.
The typical radar echoes observed during the lifecycle of a bow echo is shown in Fig. In long-lived bow echoes, the Coriolis force promotes stronger cyclonic shear behind the poleward end of the bow and weak anticyclonic shear equatorward of the bow Fig. The association of MCCs with devastating flash floods has been recognized since the late s. MCCs exhibit mean cloud shield areas of , km 2 and persist for an average of 11h. Oceanic MCCs are, on average, slightly larger and longer lasting.
Like other MCSs, convection begins in the late afternoon and peak precipitation rates over 25mm h-1 occur in the h period after initiation. As the MCC matures, the total rain rate decreases, becomes more stratiform, as the rain area expands.
After hours, rainfall ends and deep convection ceases in the early-to-late morning. Near maximum mean upward motion, upper tropospheric divergence, and vorticity occur throughout the mature stage and is maintained through the decay stage. The decaying MCC leaves significantly amplified mid-level convergence and vorticity; at the upper-levels it leaves an anomalous upper-tropospheric high and wind perturbations extending beyond the MCC boundary.
Thus, MCCs have the ability to attain inertial stability and last for more than a diurnal cycle and influence the large-scale environment in which they form. While squall lines have distinctive linear structure, non-squall tropical cloud clusters are less organized, appear amorphous in radar images, and move more slowly Fig. The large-stratiform anvil of tropical non-squall clusters sometimes meets the MCC criteria.
The general lifecycle of MCSs is influenced by the diurnal cycle and modulated by elevated terrain, coastal topography, and the large-scale environment. Satellite cold cloud perspective shows a similarly nocturnal lifecycle for large MCSs. Unlike individual thunderstorms, MCSs develop mesoscale circulations that may become inertially-stable, i. In some regions, the diurnal cycle of MCSs is coincident with the evolution of a nocturnal low-level jet, which supplies the MCSs with moist air during nighttime.
Early in the lifecycle and in the afternoon to evening, convective precipitation dominates. As the MCS matures, the total rain rate decreases, becomes more stratiform, as the rain area expands.
Oceanic MCSs reach their peak intensity in the early morning, for reasons that are remain debatable. It considers the variations in the near surface layer and its evolution in response to deep convection. Then, the next day, deep convection is inhibited as the near surface layer is stabilized in the wake of the MCS precipitation and the ocean is shaded by the remnant cloud shield. The MCS diurnal cycle is also influenced by whether the monsoon is in "active" or "break" "active" or "break" mode.
For example, during the active monsoon when deep zonal westerlies dominate over northern Australia, MCSs reach their maximum area in the late morning, a characteristic that is more typical for maritime convection. While during the break phase, when zonal flow is easterly, the MCS areal extent peaks in the early afternoon, which is more typical for convection over land.
While the main ingredient for cumulus convection is moist air that is warmer than its environment Section 5. In general, tropical MCSs develop in environments with weaker cold pools and weaker horizontal wind shear than the midlatitudes. Both tropical and midlatitude MCSs have weak or straight-line mid-level shear profile with most of the vertical wind shear found in the low-levels often generated by a low-level jet.
The and hPa shear in non-squall tropical clusters the least intense MCSs is less than 5 m s -1 while tropical squall lines with bow echoes which have the highest likelihood of strong, straight-line surface winds have mean shear of about 13 m s By comparison, 10 m s -1 is the upper threshold for weak shear environments in midlatitude MCSs.
Without strong low-level shear, lines form parallel to the low-level shear Panel 3 , while more complex structures occur with strong low and mid-level shear Panel 4.
In MCSs with a trailing stratiform region, updraft speeds range from m s -1 in the convective region and cm s -1 in the stratiform region. Mesoscale downdrafts, in the stratiform region, of the typical tropical MCS are in the cm s -1 range. How do these MCS features form and evolve? For a typical environment of strong low level shear, the updraft would then be of a layer ascending on a slantwise path through the storm.
A layer of 3- to -6 km inflow is then drawn up through the system as a gravity wave response to the heating. The layer of inflow air enters the convective region, rising and exiting as the middle to upper level front-to-rear flow.
The pre-squall environment is marked by a moist boundary layer, moderate-high CAPE, low level of free convection Fig. As the squall line passes, the following features are observed: a pre-squall mesolow due to subsidence warming in the mid-to upper troposphere , a mesohigh due to heavy precipitation and convective-scale downdrafts , and a wake low due to subsidence warming and as a surface expression of the descending rear inflow jet Fig.
Post squall environments are characterized by subsidence, adiabatic compression, which warms and dries the lower troposphere, as indicated by an onion-shaped sounding Fig. A squall line example is shown but the process is similar for other MCSs.
Tropical squall line development is aided by strong low-level wind shear for GATE squall lines, the critical threshold was 13 m s -1 in the hPa layer, mostly perpendicular to the leading line. Squall lines, in turn, transport momentum upgradient , increasing the low-level vertical wind shear. The organizational mode of the squall line, e. The convectively-generated cold pool acts as a gravity current because it is denser than its environment.
New convection is formed by uplift along the boundary of the cold pool. Its speed is given by:. Gust fronts can precede storm cells of a few tens of km 20 to 40 km. Normally, the density current head has a rotor circulation. It is often thinner over the ocean m than over continents up to 3 km.
The moisture content also falls. When the shear vorticity is balanced by the cold pool vorticity, the updraft remains upright, the cold pool triggers lifting, and the convective system is long-lived , Fig.
How the stratiform region evolves reflects the orientation of the vertical shear vector relative to the squall line motion Fig. The commonly observed trailing stratiform type develops where dominant shear is perpendicular to the line. The parallel stratiform region has more line parallel shear in the upper-levels and the leading stratiform has weaker low-level shear than the other two types Fig. It is not clear how the archetypes can be applied generally in the tropics given the generally weaker shear compared with the midlatitudes.
At the large-scale, the dominant forcing of squall clusters in the western Pacific and tropical Atlantic is convergence in the ITCZ. Squall clusters also occur with easterly waves, which are noted for having low-level convergence, divergence above hPa, and non-divergence in between. They normally form ahead of the easterly wave trough, move at about twice the speed of the wave, and tend to die just behind the ridge.
Amazon squall lines have added mesoscale forcing from the sea breeze front. Bow echoes most commonly occur in an environment with strong deep layer shear in combination with high CAPE, steep midlevel lapse rates, and a strong cold pool.
Bow echoes sometimes develop within pre-frontal squall lines and tropical cyclone rainbands. Development is favored when a convectively-generated surface cold pool combined with substantial low-level vertical wind shear leads to a deep layer of slantwise ascent and a large stratiform cloud region.
Most of the wind shear in MCC environments is found in the low-levels often generated by a low-level jet.
MCC formation can happen with or without large-scale forcing Fig. If the sign of cold-pool-induced circulation is always the same as that associated with the ambient shear then the convection will be long-lived.
This secondary mechanism Fig. In that region, MCCs are associated with the monsoon trough and are often precursors to tropical cyclones. A local maximum in absolute humidity and a local minimum in static stability favored MCC initiation. Low-level convergence, upper-level divergence, and a mid-level vorticity maximum, and weak mid-level shear are also characteristic of the mean genesis environment.
There, favorable strong low-level convergence and low-level wind shear are produced from the interaction of northeast monsoon winds and the sea breeze Fig. Then it is suggested that thermally-forced gravity waves propagate offshore and initiate MCCs during the nighttime.
A distinctive feature of non-squall cluster environments is the absence of strong shear between and hPa. They have deep layer moisture and maximum low-level convergence during the growing stage of the system lifecycle. Maximum vertical motion is close to hPa and occurs during the mature phase. During GATE, clusters formed where the mean hPa environmental shear was about 6 m s -1 and mostly parallel to the lines. Non-squall clusters are similar to squall clusters in terms of conditional instability and formation relative to the African easterly wave trough.
However, large, longer-lived non-squall clusters tend to move at less than the speed of the easterly wave and dissipate once they fall behind the trough axis. Similar winter monsoon clusters near Borneo are initiated from offshore breezes and a quasi-stationary vortex that develops cross-equatorial monsoon flow Section 3.
MCSs propagate and remain coherent via a number of methods: discrete propagation along outflows from baroclinic boundary circulations, low-level jet processes, gravity-wave interactions, and other larger-scale forcing mechanisms. MCS motion will follow the synoptic flow until a significant cold pool develops, which is almost coincident with the forming of the MCS stratiform anvil. This larger cold pool then acts as a gravity current and lifts unstable air upward, thereby generating new convection on the leading edge of the MCS.
Discrete propagation is another suggested mechanism. Once the cold pool is established, it is important to understand the low-level jet a prominent feature in MCC environments in order to predict the system motion. The low-level jet is a narrow band of strong winds at or near km above the ground. Some are nocturnal jets that persist into the morning and others are seasonal or synoptically forced. Areas of prominent low-level jets solid blue shade around the globe and associated regions of MCS activity dashed boxes are shown in Fig.
A new line of convection will form some distance from the MCS cold pool, towards the region of the low-level jet, which provides the moist air for maintenance of the MCS.
Tropical MCSs are modulated by large-scale circulations such as easterly waves easterly waves , equatorial waves, 81 , , and the MJO. Systems observed during GATE formed several hours after large-scale convergence was established and moisture flux increased in the low-middle troposphere.
The variability of MCSs has more to do with regional thermodynamics, such as CAPE, convection initiated by elevated heating, and dynamics e. Kelvin waves, which move eastward along the equator, are noted for having large and more intense MCSs within their wet phase and very little organized convection during the dry phase. Notice that the MCSs are forming each day within the Kelvin wave envelope.
Similarly, the planetary scale MJO, also affects the propagation and organization of MCSs and other convective systems. Conversely, mesoscale convection affects the large-scale systems through heat, moisture, and momentum transport. Long-lived MCSs are an important link between the convective and large-scale atmospheric circulation because they modify the vertical distribution of heating and moisture. Except over subtropical oceans, MCSs are larger at sunrise than at sunset.
The total population forms a continuous, approximately log normal, distribution with the frequency inversely proportional to the area and intensity.
No significant relationship was found between size and intensity. More recent climatologies from the TRMM satellite have found similar characteristics. MCS rainfall is beneficial for agriculture during the growing season but is also often hazardous because they cause devastating flash floods e. They are the main precipitation source in the semi-arid African Sahel 57 , Fig.
Over the western Amazon, large MCSs comprise a small fraction of convective systems but they contribute most of the cloud cover and precipitation. MCSs are associated with numerous hazards including damaging winds, heavy rainfall and flash floods, hail Fig. The severity and types of hazard depends on the organization mode of the MCS.
Convection has a greater impact on the large-scale when organized into mesoscale systems than as individual thunderstorms. This is particularly evident in the vertical distribution of heating due to latent heat and radiation Fig. In order to quantify the vertical transport of heat and moisture, it helps to consider an ensemble of cumulus clouds embedded in a large-scale circulation. The stratiform precipitation exerts great influence on the overall vertical heating profile. The intense but smaller convective region has updrafts from the boundary layer up to the equilibrium level and precipitation downdrafts only in its lowest levels.
Net heating results from latent heat released during condensation Fig. In contrast, the stratiform region has a large region of ascent, from layer lifting and older updraft elements spreading out from the convective region, and downdrafts below the melting layer.
The resulting stratiform profile has warming above and cooling below due to melting and evaporation beneath cloud base Fig. The arrangement of convective and stratiform regions means that the net MCS heating is concentrated in the middle to upper troposphere. The larger the percentage of stratiform region in an MCS, the higher the level of maximum heating. The heating profile will also be affected by the relative amounts of shallow versus deep convection present in the MCS.
Therefore it is not surprising to find out that heating profiles vary among regions. Maximum heating in western Pacific MCSs occurs in the mid-upper levels during the mature-to-decaying stages while GATE systems experience maximum heating earlier and in the lower troposphere. One of the most important aspects of deep convection is its influence on the tropospheric radiation budget. Tropical mean humidity and radiative fluxes are dependent on the degree of convective aggregation.
Because the stratiform region of MCSs is broad and long lasting, it is also affected by radiative heating and cooling Fig. A tropical MCS can cause net cooling from solar extinction which outweighs warming inside the system.
What time of day MCSs occur can change the radiative balance. Even with constant total cloud fraction, the sign of the radiation balance is sensitive to the diurnal distribution of deep convective cloud systems. Differential radiative heating can alter the evolution and mass circulation of individual MCSs through feedback among latent heat release, convective updrafts, and precipitation.
The extensive stratiform anvil and nocturnal lifecycle of many MCSs affect the radiation balance local and regionally and may have implications for the global energy balance. Why is heating in MCSs important?
The response of the atmosphere to latent heat depends on the horizontal scale of the heating relative to the Rossby radius of deformation, L R. If the horizontal scale of heating is less than L R , then most of the energy released by heating will propagate away from the disturbance as gravity waves. If the scale of the latent heating is close to or exceeds L R , then energy maintains nearly geostrophically-balanced flow.
Tropical MCSs can become long-lived and influence the large-scale circulation when they are dynamically close to L R.
Diabatic heating in MCSs can force upper-level jet streaks downstream by enhancing ageostrophic flow in the jet entrance. A continental-scale adjustment can favor more convection and flooding. Under certain conditions, series of MCSs regenerate, in roughly the same location and follow similar tracks, thereby aggravating their flood potential.
Spiral bands of midlevel clouds are sometimes observed on satellite images after the decay of the active convection in MCS. The occurrence of tropical cyclone-like structures on land has been documented since the late s. The cyclonic circulation is centered on a warm-core, mesoscale convective vortex MCV that sometimes develops in the mid-troposphere, in the stratiform region of MCSs , , , Fig. These vortices were first noticed in tropical MCSs but have since been widely documented for warm season midlatitude continents.
The development can be examined in terms of PV theory, which dictates that mass-integrated PV remains constant between two isentropic surfaces regardless of changes in mass transport or diabatic heating.
The potential vorticity for frictionless flow can be written as:. Therefore, when diabatic heating occurs in moist convection, evacuation of mass across isentropes will lead to an increase in PV, i. With saturated air in the stratiform region, the Rossby radius is smaller as the buoyancy frequency is determined by the moist static stability. Then they last for hours and decay unless convection is maintained or recurs.
As a dynamical response to heating on the order of the Rossby radius, the MCV can become inertially stable Fig. Heating in the positive PV anomaly can persist for days, regenerating convection and amplifying the vortex. MCVs will persist in the presence of weak synoptic flow, weak vertical wind shear, and strong gradients of humidity.
The example in Fig. It has been theorized that when successive cycles of convection occur over a warm water surface, they can play a crucial role in the transition of a loosely organized cluster of convection into a tropical depression, provided the large-scale environment is favorable Chapter 8, Section 8.
Chapter 8, Section 8. Tropical cyclones sometimes form when MCSs move over water, probably due to midlevel vortices extending downward. Most tropical cyclone circulations are synoptic-scale but their precipitation structure and inner core dynamics are predominantly mesoscale Chapter 8, Section 8. Satellite microwave measurements suggest that mesoscale convective bursts can lead to rapid changes in cyclone intensity and structure through latent heat feedback mechanisms.
MCS are a major source of lightning. During the passage of a typical tropical squall line, the leading convection is characterized by negative cloud-to-ground CG lightning Fig. As the system matures and the stratiform region expands, large amplitude positively charged flashes become prevalent Fig. Since the early s interest has grown in other electrical properties of MCSs, particularly their association with upper atmospheric transient luminous events known as sprites, blue jets, and elves.
A necessary but not sufficient condition for sprites is an MCS with stratiform precipitation area over 20, km 2. The three tropical continental regions are prominent sources of lightning , and sprites. Africa is the most outstanding in terms of mesoscale lightning, flashes with extraordinary energy and vertical charge that excites sprites in the mesosphere. In the Congo, squall lines with large stratiform regions also have highly energetic, positive lightning and attendant sprite initiation but are less intense than MCSs in West Africa.
West Africa has stronger baroclinicity, large-temperature gradients between the hot, Saharan air and the cool, moisture air to the south, compared with the more barotropic environment over the Amazon. Mesoscale convection is important for the transport and chemical cycling of trace gases. The convective updraft displaces the tropopause upwards leading to strong vertical mixing.
This displacement, along with a broken tropopause around the edges, injects ozone-poor tropospheric air into the stratosphere. Lightning in thunderstorms helps to create nitrogen oxides NO x , primary sources of fixed nitrogen in the atmosphere that are critical to the production of tropospheric ozone, and affects the concentration of the hydroxide radical OH and hence can modulate oxidizing in the atmosphere.
MCSs readily carry NO x to the upper troposphere, where it can remain for days , and be transported over long distances, increasing the potential for ozone production in areas with limited NO x. In the Amazon Boundary Layer Experiment , ozone concentrations in the mid-upper levels of squall lines were times above background values.
For example, Fig. The pattern identifies regions where island and mountain effects dominate. Chapter 5, Section 5. Sea and land breezes, which are among the most commonly observed local circulations, are initiated by differential heating over land and ocean Fig.
The radius of the cloud-free ring is usually comparable to the width of the island. The Coriolis Effect helps to constrain the horizontal effects of the land-sea breeze by turning the wind, which limits its inland-offshore influence. In the tropics, the Rossby radius of deformation Rossby radius of deformation , the length scale at which rotational or Coriolis Effect become as important as buoyancy effects, is nearly an order of magnitude larger than in the midlatitudes.
So a circulation such as the sea breeze can have a much larger horizontal extent in the tropics without being turned by the Coriolis acceleration. The sea-breeze flow will converge or diverge depending on the shape of the coastline.
Convergence produces stronger thunderstorms, e. Convergence of land breezes from neighboring islands or continents can form intense thunderstorms Fig. In the South China Sea, offshore thunderstorms are formed where the low-level jet converges with the land breeze or gravity waves produced by previous convection over land Fig.
Much like the sea breeze, heterogeneous heating of the land areas with steep topography leads to mesoscale thermal circulations Fig. During the daytime, heating of elevated terrain leads to rising motion over the mountains, condensation, and precipitation. This sets up a circulation, known as a mountain breeze, between the mountain and the lower elevation, with low-level convergence over the mountain and divergence over lower elevation.
During nighttime, the mountain areas cool and air sinks into the lower elevation, forming a valley circulation. Steep terrain also serves as a lifting mechanism and a source of new convection. Therefore, the windward side of mountains will be wetter than the leeward side. For example, because of the prevailing easterly trade winds, the Eastern Caribbean islands are wet on the east and drier on the west.
Accumulated precipitation maxima are aligned along the eastern mountain slopes Fig. Under light winds or calm conditions, convection is more centered over the high terrain. With inland lakes and mountains, local circulations are more complex.
For example, the Lake Victoria area Fig. On average, the diurnal cycle has thunderstorms over the eastern part of the lake during daytime and over the west during night and early morning. Channeling of flow by high terrain creates wind maxima known as gap winds, coastal jets, and low-level jets, depending on location. Some effects are straightforward, such as the acceleration of trade winds and northers through isthmuses in the Central American Mountains. A complex topographic effect occurs along the north-south Annam Cordillera on the east coast of Indochina.
This causes cool upwelling that is enhanced by Ekman upwelling due to the cyclonic curl of the wind stress on the north side of the jet, leading to cooler SSTs just north of the jet axis. Another well-known wind maximum occurs in the Gulf of Tehuantepec in southern Mexico. As northerly winds move south behind cold fronts in the Gulf of Mexico, flow accelerates through the Chivela Pass in southern Mexico leading to gale-force winds over the Gulf of Tehuantepec in the Pacific Fig.
Islands disrupt the organization of tropical oceanic clouds, which typically have two dominant directional modes: cloud streets aligned parallel to the low-level wind and, less frequently, aligned at large angles to the low-level wind, but not necessarily at right angles.
Convergence in the wake promotes convection and precipitation. The direction of the wake vortex depends on the direction of the trade winds. With east-or east-northeasterly winds, the wake vortex from Barbados extends to St. Vincent and the Grenadines Fig. When winds are southeasterly the wake vortex from Barbados extends to St.
Another prominent example of island induced circulations is flow blocking by Taiwan during the summer monsoon. The blocked flow produces a low-level jet northwest of the island and lee vortices downstream, both of which influence where precipitation occurs. Similar local circulations are generated by flow around the big island of Hawaii in the north central Pacific. While thunderstorms occur in many parts of the tropics, severe thunderstorms are rare.
Severe thunderstorms, defined by the U. Why is this type of severe weather rare in the tropics? Severe thunderstorms thrive in strong vertical wind shear and horizontal gradients of moisture, temperature, and wind.
Furthermore, vigorous convection that produces hail and tornadoes require dry, cool mid-levels above an inversion that caps warm, moist near surface air and lead to strong updrafts when the inversion is eroded. Temperature and moisture are fairly homogeneous in the tropical environment. Tropical updrafts are weaker than midlatitude continental updrafts, limiting hail growth, and the vortex stretching that is sufficient to produce tornadoes.
A tornado is a violently rotating column of air, extending from a cumulonimbus or cumulus congestus and reaching the surface Fig.
It is the most destructive local scale atmospheric phenomenon. Tornadoes last from seconds to more than an hour and their paths range from m to 10s of km.
Although relatively rare, tornadoes occur on all continents except Antarctica Fig. They are most common in the plains of North America and Australia. Few tropical places have extensive storm-data reporting like the US. From the tropics, India recorded 42 tornadoes from to while Cuba had a mean of 41 tornadoes per year from to In Cuba and the Florida peninsula most tornadoes occur during June and July, mainly associated with waterspouts moving onshore and tropical cyclones at landfall.
In India and Bangladesh tornadoes are most frequent during April and May and rarely occur during the monsoon.
Strong tornadoes are most common in spring and in the late afternoon, but can occur in any season and at any time of day. The scale is named for Dr. Theodore Fujita who created the first tornado intensity scale in The original Fujita Scale F scale was based on the damage caused by a tornado. The original F-scale was limited by factors such as: categories based on the worst damage, even if done to a single structure, and failure to account for differences in construction. The EF scale starts with a list of 28 damage indicators that includes a description of the typical construction for that indicator category.
Tropical tornadoes are usually weak, EF0 or EF1. Only a small percentage of tornadoes are extremely intense, EF3 or greater and they mainly occur with supercells in the midlatitudes. Tornadoes in the tropics are typically produced by non-supercell thunderstorms, landfalling tropical cyclones, extratropical systems that extend into the tropics, subtropical lows, and hybrids of tropical and extratropical systems.
Most tropical tornadoes are weak and not produced by supercells. The parent cloud does not have a mesocyclone as found in supercells. As illustrated conceptually Fig. When a moist convective updraft becomes co-located with a misocyclone, it becomes a tornado through vertical stretching of the vorticity along the boundary. A misocyclone, a small cyclone generated by horizontal shear instability and convergence in the boundary layer, is distinct from the larger and deeper mesocyclone, the rotating updraft in a supercell, which is due to the tilting of horizontal vorticity produced by vertical wind shear.
Non-supercell tornadoes can form even when the low-tropospheric circulation is weak. Once the updraft is established, with rapid convective growth, a tornado can be produced. In Fig. The tornado formed at the convergence zone between the two boundaries. Supercell thunderstorms are rare in the tropics, occurring only under extraordinary conditions.
However, because of their highly hazardous weather, their characteristics and conditions under which they may occur in the tropics need to be understood by tropical meteorologists. A supercell thunderstorm is an intense, relatively large thunderstorm km scale that produces severe weather and can last for several hours. Supercells are noted for generating the strongest tornadoes, large hail, strong winds, and heavy rain. Furthermore, the inland penetration distance was related to the strength of the maximum vertical velocity within the front.
In addition, sensitivity tests showed little change in the modeled breeze when measured surface temperatures for Lake Michigan were used as initial conditions and boundary conditions in the place of surface skin temperature as derived by the National Centers for Environmental Prediction.
Raising the lake temperatures significantly in the simulation yielded a more elongated vertical circulation and a briefer lake-breeze event that did not reach as far inland. Copyright of Journal of Applied Meteorology is the property of American Meteorological Society and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission.
However, users may print, download, or email articles for individual use. Google Scholar Angevine, W. Google Scholar Arritt, R. Google Scholar Atkins, N.
Google Scholar Atkinson, B. Google Scholar Banta, R. Google Scholar Bechtold, P. Google Scholar Cats, G. Google Scholar Csanady, G. Google Scholar Defant, F. Google Scholar Driedonks, A. Google Scholar Elliot, W. Google Scholar Estoque, M. Google Scholar Finkele, K. Google Scholar Garratt, J. Google Scholar Grisogono, B. Google Scholar Gustafson, N.
Google Scholar Lundin, K. Google Scholar Mahrer, Y. Google Scholar Melas, D. Google Scholar Mellor, G. Google Scholar Mohr, M. Google Scholar Mulhearn, P.
Google Scholar Nielsen, N. Google Scholar Rotunno, R. Google Scholar Smedman, A. Google Scholar Steyn, D. Google Scholar Stunder, M. Google Scholar U. Google Scholar Walsh, J. Google Scholar Wexler, R. Google Scholar Xian, Z. Google Scholar Yan, H. Google Scholar Zhong, S.
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