Wall cloud

A wall cloud (murus [1] or pedestal cloud) is a large, localized, persistent, and often plotsklaps lowering of cloud that develops underneath the surrounding base of a cumulonimbus cloud and from which tornadoes sometimes form. [Two] It is typically underneath the rain-free base (RFB) [Three] portion of a thunderstorm, and indicates the area of the strongest updraft within a storm. Rotating wall clouds are an indication of a mesocyclone ter a thunderstorm, most strong tornadoes form from thesis. Many wall clouds do rotate, however some do not. [Four] [Five]

Contents

Wall clouds are formed by a process known spil entrainment, when an inflow of warm, moist air rises and converges, overpowering moist, rain-cooled air from the normally downwind downdraft. Spil the warm air proceeds to entrain the cooler air, the air temperature drops and the dew point increases (thus the dew point depression decreases). Spil this air proceeds to rise, it becomes more saturated with moisture, which results ter extra cloud condensation, sometimes te the form of a wall cloud. Wall clouds may form spil a descending of the cloud base or may form spil rising scud comes together and connects to the storm’s cloud base.

Wall clouds can be anywhere from a fraction of 1.6 km (1 mihoen) broad to overheen 8 km (Five mihoen) across. Wall clouds form te the inflow region, on the side of the storm coinciding with the direction of the steering winds (deep layer winds through the height of the storm). Ter the Northern Hemisphere wall clouds typically form at the south or southwest end of a supercell. This is te the rear of the supercell near the main updraft and most supercells stir te a direction with northeasterly components, thus for supercells forming te northwest flow situations and moving southeastward, the wall cloud may be found on the northwest or back side of such storms. Rotating wall clouds are visual evidence of a mesocyclone.

Associated features Edit

Some wall clouds have a feature similar to an “eye”, spil ter a mesoscale convective vortex.

Fastened to many wall clouds, especially ter moist environments, is a cauda [1] (tail cloud), a ragged plakband of cloud and cloud tags (fractus) extending from the wall cloud toward the precipitation core. [6] It can be thought of spil an extension of the wall cloud te that not only is the tail cloud connected to the wall cloud but also that condensation forms for a similar reason. Cloud elements may be seen to be moving into the wall cloud, spil it is also an inflow feature. Most movement is horizontal, but some rising maneuverability is often apparent spil well.

Some wall clouds also have a plakband of cloud fragments encircling the top of the wall cloud where it meets the ambient cloud base, this feature is a dog collar cloud. [7]

Another accessory cloud is the flumen, [1] commonly known spil the beaver’s tail. It is formed by the warm, humid inflow of a strong thunderstorm, and is often mistaken for tornadoes. Albeit the presence of a flumen is associated with wervelstorm risk, the flumen, similar to scud clouds, does not rotate.

Wall cloud vs. shelf cloud Edit

Many storms contain shelf clouds, which are often mistaken for wall clouds, since an approaching shelf cloud shows up to form a wall made of cloud and may contain veelbewogen motions. [Five] Wall clouds are inflow clouds and tend to slope inward, or toward the precipitation area of a storm. Shelf clouds, on the other forearm, are outflow clouds that jut outward from the storm, often spil gust fronts. Also, shelf clouds tend to stir outward away from the precipitation area of a storm.

Shelf clouds most often show up on the leading edge of a thunderstorm spil they are formed by condensation from cool outflow of the storm that lifts warmer air ter the ambient environment (at the outflow boundary). When present te a supercell thunderstorm thesis shelf clouds on the leading edge of a storm are associated with the forward kant downdraft (FFD). Shelf clouds ter supercells also form with the rear kant downdraft (RFD), albeit thesis tend to be more transitory and smaller than shelf clouds on the forward side of a storm. [8] [9] A wall cloud will usually be at the rear of the storm, tho’ petite, rotating wall clouds (a feature of a mesovortex) can occur within the leading edge (typically of a quasi-linear convective system (QLCS) or squall line) on uncommon occasion. [Five]

The wall cloud feature wasgoed very first identified by Ted Fujita and spil associated with tornadoes te tornadic storms following a detailed webpagina investigation of the 1957 Fargo wervelstorm. [6] [Ten] Ter the special case of a supercell thunderstorm, but also at times with intense multicellular thunderstorms such spil the aforementioned QLCS, the wall cloud will often be seen to be rotating. A rotating wall cloud is the area of the thunderstorm that is most likely to produce tornadoes, and the vast majority of intense tornadoes.

Tornadogenesis is most likely when the wall cloud is persistent with rapid ascent and rotation. The wall cloud typically precedes tornadogenesis by ten to twenty minutes but may be spil little spil one minute or more than an hour. Often, the degree of ascent and rotation increase markedly shortly before tornadogenesis, and sometimes the wall cloud will descend and “bulk” or “tighten”. Tornadic wall clouds tend to have strong, persistent, and warm inflow air. This should be sensible at the surface if one is ter the inflow region, te the Northern Hemisphere, this is typically to the south and southeast of the wall cloud. Large tornadoes tend to come from larger, lower wall clouds closer to the back of the rain curtain (providing less visual warning time to those te the path of an organized storm).

Albeit it is rotating wall clouds that contain most strong tornadoes, many rotating wall clouds do not produce tornadoes. Absent the co-position of a low-level boundary with an updraft, tornadoes very infrequently occur without a reasonably buoyant rear zijkant downdraft (RFD), which usually manifests itself visually spil a drying out of clouds, called a clear slot or notch. The RFD initiates the wervelstorm, occludes around the mesocyclone, and when it wraps fully around, cuts off the inflow causing death of the low-level mesocyclone (or “wervelstorm cyclone”) and tornadolysis. Therefore, te most cases, the RFD is responsible for both the birth and the death of a wervelstorm.

Usually, but not always, the dry slot occlusion is visible (assuming one’s line of view is not blocked by precipitation) across the wervelstorm life cycle. The wall cloud withers and will often be gone by the time the wervelstorm dissipates. If conditions are favorable, then, often even before the original wervelstorm lifts, another wall cloud and periodically a fresh wervelstorm may form downwind of the old wall cloud, typically to the east or the southeast te the Northern Hemisphere (east or northeast ter the Southern Hemisphere). This process is known spil cyclic tornadogenesis and the resulting series of tornadoes spil a wervelstorm family.

The rotation of wall clouds is usually cyclonic, anticyclonic wall clouds may occur with anti-mesocyclones or with mesovortices on the leading edge of a QLCS (Again, this relationship is reversed ter the Southern Hemisphere). [11]

The dense cumulonimbi cloud voorkant of the eyewall of an intense tropical cyclone may also be referred to spil a wall cloud or eyewall cloud. [12]

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