Wall Cloud Research Articles

Surface Meteorological Observations in Severe Thunderstorms. Part II: Field Experiments with TOTO

The TOTO (Totable Tornado Observatory) device was field tested in the Southern Plains by a severe-storm intercept team from the University of Oklahoma from late May through early June 1981. The results from two intercept missions and a gust-front intercomparison at the National Severe Storms laboratory are discussed. Measurements are presented of wind speed, wind direction, pressure and temperature made underneath a rotating wall cloud and within 1.5 km of two tornadoes. A damage survey and a Doppler-radar observed mesocyclone-signature track were used in conjunction with the TOTO data to obtain an estimate of the maximum wind speed inside one of the tornadoes.

Polygonal Eye Walls and Rainbands in Hurricanes

Abstract It was noted from analyses of radar data obtained in hurricanes that both the spiral bands and the inner boundary of the wall cloud frequently were composed of a series of straight line segments. Indeed, the eye of a strong hurricane is frequently polygonal rather than circular or elliptical. These features may have a possible kinematic explanation based an interference among differing wavenumbers and frequencies of internal gravity waves.

Positive cloud‐to‐ground lightning flashes in severe storms

The occurrence of cloud‐to‐ground flashes that effectively lower positive charge to earth (+CG flash) over flat terrain has been documented in the mature stage of severe thunderstorms. Of the 31 documented +CG flashes, most had only one return stroke. Zero‐to‐peak rise times for the strokes averaged 7 µs. The +CG flashes averaged 520 ms in duration, with 25 percent lasting more than 800 ms. Many of these had field changes suggestive of continuing current. Positive flashes have been observed to emanate from several regions of severe storms: high on the back of the main storm tower, through the wall cloud, and from the downshear anvil. Visually most of these positive flashes have emanated from high in the storm, and acoustic mapping of two shows thunder sources to a height of about 15 km.

Storm Motion as Related to Boundary-Layer Convergence

Data presented indicate that severe thunderstorm areas may become anchored to intense, boundary- layer convergence zones. In such cases. the mean cloud-layer wind vector has little relation to the movement of regions of large hail, wall clouds and tornadoes. Suggestions for improving severe thunderstorm warnings are offered based on this possibility.

Hurricane tritium II: Air-sea exchange of water in Betsy 1965

The radial and vertical distribution of tritium (as HTO) in rain water and in water vapor was investigated in hurricane Betsy on four days, each day having different storm characteristics. On one day, 3 September, stratospheric subsidence was detected in the eye. The tritium concentration of underlying seawater was also measured. The molecular exchange of water at the air/sea interface was clearly exhibited on all four days, and the extent of exchange increased with increasing storm intensity. On 3 September the wall cloud vapor had a composition equivalent to 86% seawater vapor and 14% vapor from outside the storm envelope. Together with the measured radial distribution of total wind velocity and reasonable assumptions of the effect of spray on rate of exchange, the tritium data were used to calculate possible distributions of relative inflow angle and of specific vapor inflow. A maximum in the inflow function around 120 km was obtained in one case, indicating subsidence between 200 km and 120 km. In the same area the distribution of tritium changes drastically from a vertical gradient to vertically well mixed and a horizontal gradient. DOI: 10.1111/j.2153-3490.1968.tb00401.x

SOME UNUSUAL ASPECTS CONCERNING THE DEVELOPMENT AND STRUCTURE OF TYPHOON BILLIE—JULY 1967

Abstract Typhoon Billie exhibited mesoscale warm-core characteristics and developed winds of typhoon intensity without ever forming a wall cloud around the eye. Clouds that swirled into the storm center were flattened cumulus and stratocumulus with cloud tops at 4,000 to 5,000 ft. It was clear of all higher cloudiness in the area of the eye. The storm center lay on the northern edge of major overcast cloudiness and its appearance was similar to that of an intense Stage C tropical cyclone. Satellite pictures together with conventional analyses and information gathered by the author as a pilot on reconnaissance missions into the storm indicate that Billie intensified to typhoon strength as a result of mesoscale changes in the area of the eye. It is suggested that Billie represents a type of typhoon whose maximum wind speeds are limited because of failure to develop an encircling wall cloud.

Hurricane tritium II: Air-sea exchange of water in Betsy 1965

The radial and vertical distribution of tritium (as HTO) in rain water and in water vapor was investigated in hurricane Betsy on four days, each day having different storm characteristics. On one day, 3 September, stratospheric subsidence was detected in the eye. The tritium concentration of underlying seawater was also measured. The molecular exchange of water at the air/sea interface was clearly exhibited on all four days, and the extent of exchange increased with increasing storm intensity. On 3 September the wall cloud vapor had a composition equivalent to 86% seawater vapor and 14% vapor from outside the storm envelope. Together with the measured radial distribution of total wind velocity and reasonable assumptions of the effect of spray on rate of exchange, the tritium data were used to calculate possible distributions of relative inflow angle and of specific vapor inflow. A maximum in the inflow function around 120 km was obtained in one case, indicating subsidence between 200 km and 120 km. In the same area the distribution of tritium changes drastically from a vertical gradient to vertically well mixed and a horizontal gradient. DOI: 10.1111/j.2153-3490.1968.tb00401.x

Temperature and Ozone Variations Near Tropopause Level over Hurricane Isbell October 1964

Temperature and ozone data obtained in hurricane Isbell on 14 October 1964 by an instrumented U-2 aircraft are used in conjunction with several radiosonde observations to reconstruct some features of the structure at tropopause level. The tropopause was inclined upwards toward the eye, with a slope of 1:200, except that the slope reached a plateau at a point over the wall clouds. In addition, it appeared that the horizontal variation of vertical motion was insignificant in the upper troposphere and lower stratosphere regions over the hurricane core. An unusual feature found in Isbell was a deep cloud-filled volume over the eye that extended from about 250 to 100 mb (the tropopause pressure).

Relationship of central pressure of hurricane Esther (1961) and the sea surface temperature field

In this report variations of central pressure of hurricane Esther are related to the sea surface temperature patterns along its track. There appears to exist a distinct relationship between central pressure variations, wall cloud intensity, and hurricane intensity to the temperature of the water over which it passes. The storm's central pressure appears to deepen over warm water and fill over cooler water. DOI: 10.1111/j.2153-3490.1962.tb01353.x

Relationship of central pressure of hurricane Esther (1961) and the sea surface temperature field

In this report variations of central pressure of hurricane Esther are related to the sea surface temperature patterns along its track. There appears to exist a distinct relationship between central pressure variations, wall cloud intensity, and hurricane intensity to the temperature of the water over which it passes. The storm's central pressure appears to deepen over warm water and fill over cooler water.

ON THE STRUCTURE OF HURRICANE DAISY ON 27 AUGUST 1958

Abstract An unusually large collection of aircraft-reconnaissance data was made in hurricane Daisy on 27 August 1958. These data consist primarily of detailed flight-level information collected by the research aircraft of the National Hurricane Research Project and radar films taken from the operational reconnaissance aircraft of the U. S. Navy. At this time, hurricane Daisy was a small, slow-moving storm off the Florida east coast with winds in excess of 100 kn in the lower troposphere. The concentrated nature of this vortex is clearly shown by the flight-level wind and temperature data and by the weather patterns shown on the radar films. The films from the search radar show a central, ring-like echo only a few miles wide which corresponds closely with the area of maximum observed winds. The height-finding radar shows this central echo—which is associated with the wall cloud surrounding the hurricane eye—to be nearly vertical and to extend above 60,000 ft.

ON THE ORIGIN OF HURRICANE SPIRAL RAIN BANDS

Abstract Analysis of the histories of spiral rain bands as observed on radar indicates that they are usually formed near the center of the storm and propagate radially outward. The rain band, therefore, maintains a quasi-conservative position relative to the quadrants in which it is formed and does not rotate about the storm center. Furthermore, the radar echoes are not simply pre-existing elements which assume the spiral shape but appear to have their origin in the outward propagated band. Data from several hurricanes are used to illustrate this hypothesis. Evidence is also presented which indicates that the eye of the hurricane is defined by a wall cloud made up of one or more spiral-band fragments in the process of generation.

EYE REGION OF HURRICANE EDNA, 1954

The eye region of Hurricane Edna (1954) is studied with the principal aid of radar and dropsonde data. Vertical sections show that over the eye there was a thick layer derived from the wall cloud which bounded the eye on the northeast. Precipitation fell from this upper layer into drier air beneath. A reasonable mechanism is thereby suggested by which large moisture values can become associated with air in the eye without producing the wet bulb potential temperatures or high winds characteristic of the rain-filled masses outside the eye. Radar data giving the height of the “bright band” or melting level show that the warm core structure of Edna was most pronounced within the radius if maximum surface winds. The result is qualitatively confirmed by soundings and by comparison of surface winds and the speeds of radar weather elements in various portions of the storm. The radar photographs also show that heavy precipitation near the eye of Edna was bounded sharply in the western semicircle along an east-west line through the center of the storm. This boundary must be associated with a rather large change of vertical air speeds and therefore has special dynamic significance.