Low-level Inversion Research Articles

A Low-Level Inversion over the AMTEX Area During a Period of Return Flow

During a four-day period the AMTEX area experiences “return flow” which was air coming from the south or Southeast, though still polar air north of the front. This air was trapped under an inversion separating it from the warm, dry air aloft. The changes of intensity and height of this inversion are discussed. The local vertical displacements of the inversion were somewhat inconsistent, rising in some regions while at the same time lowering in nearby areas. The strength of the inversion varied greatly, but the potential temperature at the top of the inversion maintained about the same numerical values.

Observations of eruption clouds from Sakura-zima volcano, Kyushu, Japan from Skylab 4

Abstract Hasselblad and Nikon stereographic photographs taken from Skylab between 9 June 1973 and 1 February 1974 give synoptic plan views of several entire eruption clouds emanating from Sakura-zima volcano in Kagoshima Bay, Kyushu, Japan. Analytical plots of these stereographic pairs, studied in combination with meteorological data, indicate that the eruption clouds did not penetrate the tropopause and thus did not create a stratospheric dust veil of long residence time. A horizontal eddy diffusivity of the order of 10 6 cm 2 s −1 and a vertical eddy diffusivity of the order of 10 5 cm 2 s −1 were calculated from the observed plume dimensions and from available meteorological data. These observations are the first, direct evidence that explosive eruption at an estimated energy level of about 10 18 ergs per paroxysm may be too small under atmospheric conditions similar to those prevailing over Sakura-zima for volcanic effluents to penetrate low-level tropospheric temperature inversions and, consequently, the tropopause over northern middle latitudes. Maximum elevation of the volcanic clouds was determined to be 3.4 km. The cumulative thermal energy release in the rise of volcanic plumes for 385 observed explosive eruptions was estimated to be 10 20 to 10 21 ergs (10 13 to 10 14 J), but the entire thermal energy release associated with pyroclastic activity may be of the order of 2.5 × 10 22 ergs (2.5 × 10 15 J). Estimation of the kinetic energy component of explosive eruptions via satellite observation and meteorological consideration of eruption clouds is thus useful in volcanology as an alternative technique to confirm the kinetic energy estimates made by ground-based geological and geophysical methods, and to aid in construction of physical models of potential and historical tephra-fallout sectors with implications for volcano-hazard prediction.

Surface ozone in Antarctica

Surface ozone measurements made in Antarctica during the 1960's show a pronounced annual variation with a summer minimum and winter to late winter maximum. Furthermore, the maximum in surface ozone precedes that in total ozone by from 3 to 5 months, the indication being a loose coupling between the Antarctic stratosphere and troposphere. The annual cycle in surface ozone, instead of reflecting changes in the Antarctic stratosphere, may be a consequence of the variation in low-level meridional transport of ozone from higher latitudes into the Antarctic continent by synoptic scale disturbances. As might be expected from a consideration of Antarctic geography and meteorology, no significant diurnal variations occur in surface ozone. The nonperiodic surface ozone fluctuations observed during the late spring and summer months at South Pole station are most likely caused by sporadic breakdowns of the low-level inversion layer. At the lower latitude stations the day-to-day variations in surface ozone are in all likelihood associated with changes in weather systems.

Título en español.

Se realizó un breve análisis de las características climáticas e hidrológicas de Puerto Rico, interrelacionadas entre sí. Mediante la selección de estaciones típicas de las regiones norte, sur, central, valles interiores y del oeste, se presenta el curso anual de las temperaturas máximas y mínimas medias, así como el correspondiente cuadro pluviométrico. Todos los valores presentados representan promedios mensuales hasta 1970, inclusive, (20 a 70 años). Se discute brevemente la incidencia de sequías y se ofrece un enfoque agrícola del balance hidrológico. Se discute, además, la aplicabilidad de índices representativos de la disponibilidad de lluvia para las cosechas.

Gravity Waves in a Low-Level Inversion

Abstract An instrumented aircraft and a vertically-pointing FM-CW radar were used to investigate waves and turbulence within a very strong low-level temperature inversion. Temperature and wind velocity data from the aircraft were spectrum-analyzed to reveal characteristics of gravity waves with lengths between 44 and 560 m. Data from two days, with slightly different inversion conditions, are presented. Nearly all the waves at these wavelengths are trapped waves, propagating horizontally within the inversion. The wave groups are generally of limited horizontal and vertical extent, often occurring wholly within thin sublayers of the inversion. The longer waves tend to have uniformity of direction, while the shorter waves propagate in all directions. Data from aircraft, radar and wind soundings are internally consistent and show that critical layer absorption of some of the waves is probable within the inversion. Some implications for the observation of gravity waves by aircraft are presented.

Low-Level Temperature Inversions in Fairbanks, Central Alaska

Abstract Low-level inversions up to 200 m were investigated on a statistical basis for Fairbanks, Alaska, using hourly data for the year March 1967 to February 1968. Surface inversions were found to be present for more than 50% of the time. In winter (November to February) there is an inversion for more than 95% of the time; maximum values of the inversion strength were 20°C in 200 m altitude difference. In summer (June to August) inversions occur relatively seldom. For the rest of the year, inversions are normally established at night, but are destroyed by day. The strength of the inversion was analyzed and shown graphically as a function of different independent meteorological parameters for the four seasons and annually. Although there are some differences depending on the season, the strength of the inversions was observed to increase with a) negative net radiation, b) decreasing cloudiness, and c) decreasing windspeed. Furthermore, during the winter a northerly wind direction, probably of orographic ...

The Life Cycle of the Dryline

Abstract The dryline, a narrow non-frontal zone of sharp moisture discontinuity, has long been known as a preferential location of thunderstorm development. Through an examination of several years of data, a conceptual model of the dryline life cycle is developed. The dryline originates along the trailing edge of a continental air mass and is coincident with an old frontal surface. As it moves, it is located on the surface projection of the western edge of the low-level inversion. The dryline is destroyed either by a new cold air outbreak or by becoming too diffuse to be easily recognizable.

The transport of sulphur dioxide over a long distance

During the winters of 1967/1968 and 1968/1969 a newly developed air pollution monitor was tried out in a field test. The sulphur dioxide concentration was continuously measured in the atmosphere of Eindhoven, a medium-sized town in the Netherlands. The town is characterized by cleanness in industry and hence the air pollution was expected to be low, especially after the large-scale change-over from the burning of coal and oil to the use of natural gas for industrial and domestic heating in the year preceding the beginning of the measurements. Generally, these expectations came true, with the exception of the high sulphur dioxide concentrations which sometimes occurred in easterly winds. They were in contrast with the relatively slight urbanization east of the measuring station. On this the hypothesis is based that high sulphur dioxide concentrations at Eindhoven may be caused by the German Ruhr area situated at 100 km distance. An analysis of the data suggests this influence. The transport of sulphur dioxide is promoted by strong winds and by either a stable atmosphere or a low-level inversion layer in the atmosphere. In addition to the influence of the Ruhr area on the sulphur dioxide concentrations there are indications of an influence of the industrial area of Antwerp. No influence from the industry of Rotterdam with its many oil refineries could be distinguished.

Air-mass dynamics or subsidence processes in the Arabian Sea monsoon

Soundings over the Arabian Sea during the International Indian Ocean Expedition period and climatological data over the west coast of India have been discussed to determine the cause of the low-level inversion and the influence of the Western Ghats on the inversion and precipitation. There does not appear relation between maximum divergence and lowest height of base of inversion as presumed by Flohnet al. The pattern of precipitation frequency on the west coast as seen from Fig. 2 of Ramage does not show the same trend either as the number of rainy days or rainfall at the coastal observatories. The depth of the moist layer and the height of base of inversion increase as the Western Ghats are approached, such changes not occurring off west Kathiawar-Kutch-Sind where there are no orographic barriers on the coast. The air-mass considerations to explain the low-level inversion over the Arabian Sea, would appear substantially valid even now.

Influence of inversions upon precipitation deposition of radioactive aerosols

The role of the tropopause as a thermal barrier to aerosol transport and direct stratospheric tapping by precipitation processes has been studied extensively. Several different transport mechanisms across this inversion, including some involving precipitation-scavenging processes, have been postulated. Gradients of radioactive aerosols are also expected across low-level inversions within the troposphere. These are generally more accessible for experimental study. Several of our studies on the meteorological influences on radioactive aerosol deposition by precipitation have involved the presence of inversions, both at the tropopause and at low levels. The inversion aspects of three prior studies are reviewed. The first involves the penetration of the tropopause by convective storms. Radiochemical and radar-meteorological analyses of two severe storms in Oklahoma in May 1963, both of which penetrated to heights above the tropopause, are compared to data for three contemporary convective storms in central Pennsylvania none of which penetrated the tropopause. The second concerns the changes in radioactivity concentration in precipitation associated with the overturning of the marine layer during a Pacific extratropical cyclone sampled at Santa Barbara, California, on February 7, 1962. The third involves an examination of the vertical distribution and transport by air motion and precipitation across the trade wind inversion at Hawaii during periods in 1963 and 1964. DOI: 10.1111/j.2153-3490.1966.tb00264.x

Influence of inversions upon precipitation deposition of radioactive aerosols

The role of the tropopause as a thermal barrier to aerosol transport and direct stratospheric tapping by precipitation processes has been studied extensively. Several different transport mechanisms across this inversion, including some involving precipitation-scavenging processes, have been postulated. Gradients of radioactive aerosols are also expected across low-level inversions within the troposphere. These are generally more accessible for experimental study. Several of our studies on the meteorological influences on radioactive aerosol deposition by precipitation have involved the presence of inversions, both at the tropopause and at low levels. The inversion aspects of three prior studies are reviewed. The first involves the penetration of the tropopause by convective storms. Radiochemical and radar-meteorological analyses of two severe storms in Oklahoma in May 1963, both of which penetrated to heights above the tropopause, are compared to data for three contemporary convective storms in central Pennsylvania none of which penetrated the tropopause. The second concerns the changes in radioactivity concentration in precipitation associated with the overturning of the marine layer during a Pacific extratropical cyclone sampled at Santa Barbara, California, on February 7, 1962. The third involves an examination of the vertical distribution and transport by air motion and precipitation across the trade wind inversion at Hawaii during periods in 1963 and 1964. DOI: 10.1111/j.2153-3490.1966.tb00264.x

The Association of Low-Level Inversions with Surface Wind and Temperature at Point Arguello

Abstract Inversions at Point Arguello, California, as detected in 4½ years by rawinsondes at 0400 and 1600 PST, are related to surface wind direction and speed and surface temperatures. Nocturnal inversions based below 1000 ft msl have their maximum frequency in winter and their minimum in summer. Most of them occur with downslope surface winds. Afternoon inversions are most frequent in July and least frequent in January. Nocturnal surface inversions appear to develop when the downslope drainage air from the interior is cool enough to undercut the marine layer. There is evidence that the critical surface temperature for this to take place is 9C.

Laser Radar Echoes from a Stratified Clear Atmosphere

As reported by two of us1, we have made numerous observations here of echoes from the ‘clear’ atmosphere, using experimental pulsed ruby laser radar. The earlier communication described returns (which we believe are due to particulate matter back-scattering) from low-level air in motion. We remarked that strong signals are commonly noted at heights corresponding to low-level inversions, revealing haze layers which are not discernible by eye. This communication describes a series of observations made in clear conditions, in which sharp discontinuities in the back-scattered signal occurring within the first 1,000 m are strongly correlated with the thermal structure.

Laser Radar Echoes from the Clear Atmosphere

USING experimental pulsed ruby laser radars, numerous observations have been made hero of echoes from the ‘clear’ atmosphere. There is no doubt that these returns are caused by backscattering from particulate matter in the aerosol. Even in the clearest conditions echoes are invariably obtained from the immediate vicinity, and these are much enhanced in hazy conditions. Strong signals are commonly noted at heights corresponding to low-level inversions, revealing haze layers which are not discernible by eye.

On interactions between the Southwest Monsoon Current and the Sea Surface over the Arabian Sea

Some aspects of interactions that take place between the water surface of the Arabian Sea and the summer monsoon circulation are investigated. Over large portions of the Arabian Sea (and also the Bay of Bengal) there is a rapid warming of the surface water during late winter and early spring. The maximum temperatures are observed around May, at the time of the establishment of the southwest on, monsoon circulation. There is then cooling of the waters to a minimum observed in August-September, followed by a secondary maximum October-November. This trend differs from what is commonly observed over most of the tropical oceans, where there is a single water temperature maximum in late summer and a minimum in late winter. The water cooling in early summer appears to be a direct result of the establishment of the southwest monsoon regime. The resulting inter-relationships have pronounced effects on the properties of both the water body and the monsoon circulation.
 
 In order to assess the role to heat flux in the water-cooling, computations of components of the energy balance were carried out for various stations in the Arabian Sea and vicinity. Rather large rates of heat flux by evaporation were obtained the west central portions of the Arabian Sea. It is shown that the evaporation makes a major contribution to the water-cooling in that area.
 
 Effects of the air-sea interactions on the atmospheric current investigated by analysis of aeteorological sounding along the monsoon surface trajectory. A characteristic low-level inversion in the levels from 900 to 700mb is found over most of the oceanic area. The moisture is concentrated below the inversion. Above the inversion the air is dry and unstable. Some of the implications of the presence of this thermal and moisture distribution on monsoon weather are discussed briefly.

Propagation at 36,000 MC in the Los Angeles basin

Fading characteristics at 36 kmc over a line-of-sight path in the Los Angeles basin have been shown to be closely correlated with meteorological conditions, particularly with the relatively persistent, low-level temperature inversion of the area. No positive evidence of the influence of atmospheric pollutants has been found, but it has been shown that suitably located microwave paths can be of value for locating and monitoring temperature inversions when they are accompanied by sufficient variation in water-vapor content. The relation of diurnal variations in propagation characteristics to diurnal variations in the temperature inversion and in atmospheric turbulence indicate that the refraction mechanism is the predominant one in causing the observed large fading amplitudes. The view is further strengthened by the relatively noncritical relation of fading to the proximity of the inversion layer.

The Breakdown of a Low-level Inversion Studied by Means of Detailed Soundings with a Modified Radiosonde

A short series of unusually detailed temperature, humidity, and wind soundings to a height of about 750 mb., made at Silver Hill, Md. on the night of October 30th and 31st, 1950, and consisting of eight flights of specially modified radiosondes and 26 double-theodolite pilot balloon runs, is presented. The nocturnal breakdown of the ground inversion with steep wind gradients, a phenomenon first remarked by Durst in 1933, is here observed apparently to be associated with the sudden lowering of an upper (turbulence or subsidence) inversion. Alternative explanations for this are advanced, and implications for minimum temperature and stratus forecasting noted. The accuracy of the observations is discussed.