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Walter A. Lyons

Abstract

NASA's Earth Resources Technology Satellite (ERTS) now provides extremely high resolution (50–200 m) multi-spectral images of any given portion of the earth (between 81° north and south latitude) every 18 days. These are the best unmanned satellite data to date for the detailed study of mesoscale cloud patterns. An ERTS view of the southern basin of Lake Michigan at 1000 CST, 24 November 1972 reveals what certainly appears to be an example of inadvertent weather modification. Cold southwesterly air flow is producing the usual cumulus cloud activity over the relatively warm lake. What is unusual, however, is that the easily visible smoke plumes from a number of major industrial complexes in the Chicago-Gary, Ind., area appear to be markedly affecting the cumulus patterns. Cloud streets developing over Lake Michigan are observed to undergo enhancement when aligned with the industrial plumes. Specifically, the cumulus elements of the cloud streets become larger and brighter (and presumably thicker) than those forming in “unpolluted” air.

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Walter A. Lyons

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Walter A. Lyons

Abstract

As part of an extensive mesoscale study of the Chicago lake breeze, ten summer months of data (1966–68) were used to compile a climatology of this phenomena and devise a simple forecasting technique. The lake breeze was found to occur at the Chicago shoreline on 36% of all days (out of a sample of 307). The time of onset ranged from before 0600 to 1&30 LST, with 0800–0900 LST being most frequent. The lake breeze front, defined as a narrow (1–2 km) band of convergence separating airflows with overland and overwater trajectories, was found to push inland anywhere from 1 block to over 40 km.

Experience verified that light gradient winds, strong insolation, and land air temperatures warmer than the lake water surface were the favorable conditions for formation. However, in an attempt to arrive at more objective forecasting scheme, the work of Biggs and Graves was extended to Lake Michigan.

A dimensionless number,
V2gCpT
is defined where V g, is the geostrophic wind speed from the 1200 GMT surface chart, C p the specific heat of dry air, and ΔT the difference (°C) between the maximum air temperatures at an inland location and the mean water temperature of the southern basin of the lake. Used as a hindcasting technique, it was found that a critical value of 10.0 emerged, above which a lake breeze would not be expected to occur at the shoreline. A hindcast accuracy between 90 and 95% was obtained by applying several additional criteria regarding the amount of cloudiness and the direction of the gradient flow with respect to the shoreline.
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Walter A. Lyons

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WALTER A. LYONS and TETSUYA FUJITA

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Over maritime areas, meteorological satellite data generally have been used only in the study of synoptic scale systems. However, TIROS 7 pictures of summertime stratus over the northern Pacific, when rectified and combined with mesoscale radiation analyses, give valuable clues regarding the mesoscale dynamics of the lower atmosphere. Radiation data distinguish stratus from middle level cloud layers. Stratus bands, averaging 15 km. wide and oriented 16° to the left of the geostrophic wind, are thought to be related to horizontal roll vortices. Reflectance cross sections cross these bands indicate sharp variations in the thickness of the stratus.

Precisely gridded photographs show the relation of marked clear areas in the stratus to the topography of the Aleutian Islands. Only when execeding a critical size do isolated mountainous islands produce clear wakes. One island appears to be shedding a possible vortex street. A derived model for the flow of the stable air over long mountain ridges in the Alentians includes such phenomena as upstream blocking, windward slope bolster eddies, and extreme turbulent mixing on the Ice slopes causing clear areas to extend over 100 km. domnstream. Radiosonde data indicate that the mixed layer downstream is approximately the depth of the obstructing ridge.

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Walter A. Lyons and Rudolph B. Husar

Abstract

An SMS/GOES 1 n mi visible image taken an 30 June 1975 reveals a massive area of atmospheric turbidity over the central and eastern United States. This was during the midpoint of a two-week air stagnation episode engulfing the Plains to the East Coast. It is shown that image “haziness” is correlated to midday surface visibility reports, which are in turn possibly correlated to sulfate aerosol concentrations. It appears that geosynchronous satellite data can play a major role in determining the areal extent of sulfate aerosol episodes.

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Walter A. Lyons and Cecil S. Keen

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Cloud-to-ground (CG) lightning observations from land-based lightning detection networks now allow monitoring this component of the electrical structure of tropical storms and hurricanes within a few hundred kilometers of the United States coastline. Several case studies confirm the long-held opinion that lightning is rather common within the outer rainbands. The general absence of CG lightning within the interior of mature tropical cyclones is also apparent. On the other hand, bursts of CG lightning near the circulation center of developing storms appear to precede periods of further deepening. The CG events are associated with convective supercells, whose anvil canopies can often obscure much of the underlying storm. Near-eyewall CG bursts preceding periods of intensification were noted in Hurricanes Diana (1984) and Florence (1988). A detailed case study of the 1987 unnamed tropical storm that struck the Texas-Louisiana coastline reveals that lightning was associated with two large supercells. These supercells appeared to be the trigger for the development of a closed circulation that formed several hours after the apparent low pressure center made landfall. Further studies of lightning may provide additional insight into the role of convective supercells in tropical storm intensification. It may also provide a useful diagnostic of impending deepening.

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Walter A. Lyons and Henry S. Cole

Abstract

Previous studies have shown that the lake breeze circulation cell which develops along the western shore of Lake Michigan during almost half of the warm season days has detrimental effects upon the air quality of the Gray-Chicago-Milwaukee area. However, stable onshore flow associated with a synoptic-scale pressure gradient occurs for an additional 15% of warm season days. This study examines the dispersion patterns during gradient, onshore flow. Fumigation and plume trapping, in particular, appear to cause serious degradation of air quality. Continuous fumigation of elevated plumes develops on days with strong insulation. Plume trapping occurs when a plume is emitted into a shallow layer of unstable air capped by a deep lid of stable air. This condition is frequent on overcast spring days.

Two days characterized by easterly gradient winds were studied: 27 May 1970, overcast; 25 June 1970, predominately sunny. The studies utilized meteorological data obtained from ground observers, ship's records, a wiresonde, and from aircraft photography.

A computer diffusion model incorporating the mesoscale meteorological characteristics for each day predicted ground level concentrations from several sources including a large coat burning power plant. The model for the fumigating power plant plume (25 June) yielded estimates in excess of 1.0 ppm SO2 7 km downwind of the plant.

Limited air monitoring data appear to confirm the diffusion model estimates and observations of plume behavior.

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Walter A. Lyons and Steven R. Pease

The Earth Resources Technology Satellite (ERTS-1) launched by NASA in July 1972 has been providing thousands of high resolution multi-spectral images of great interest to geographers, cartographers, hydrologists, agriculturists, etc. The meteorological content of these observations, however, has only been slightly realized. In particular, it has been found possible to detect the long-range (over 50-km) transport of suspected particulate plumes from the Chicago-Gary steel mill complex over Lake Michigan. The observed plumes are readily related to known steel mills, a cement plant, refineries, and fossil- fuel power plants. This has important ramifications when discussing the inter-regional transport of atmospheric pollutants, in this case from the Chicago Interstate to the Southeast Wisconsin Air Quality Control Region. Analysis reveals that the Multispectral Scanner Band 5 (0.6–0.7 μm) provides the best overall contrast between the smoke and the underlying water surface.

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WALTER A. LYONS and LARS E. OLSSON

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The lake-breeze circulation on the Great Lakes is often as vigorous as its oceanic counterpart. This paper shows that lake breezes frequently exert drastic control on mesoscale air pollution patterns in urbanized shore-line areas, in this case, Chicago, Ill. Observational data were gathered from a surface mesonetwork, surface and satellite cloud photography, a chain of pilot balloons normal to the shore, optically tracked constant-level balloons, and aircraft measurements of suspended particulate concentrations in several size ranges. On the 2 late summer days studied, the lake breezes were extremely well developed. Inflow depths ranged from 500 to 1000 m, with peak inflow velocities of 6–7 m/s. Beginning at the shore-line between 0800 and 0900 LST, the breezes penetrated inland over 40 km. Clearly defined return flow layers were present both days. Eulerian wind field measurements from serial pilot, balloon releases were used to make cross sections of the u wind component. Computed one-dimensional divergence values defined the approximate u, w streamline patterns with time. Convergence values in a narrow (1–2 km) zone at the lake-breeze front exceeded 200×10−3 s−1, and calculated upward motions reached 125 cm/s. Optically tracked tetroons yielded Lagrangian trajectory data that confirmed the basic pattern. Most importantly, the tetroons recirculated within the lake-breeze cell, describing a helical trajectory roughly centered on the shoreline. This strongly suggests that air pollutants will likewise be at least partially recirculated over the shoreline, accumulating to levels higher than would otherwise be expected.

An NCAR Queen Air instrumented aircraft took continuous cross sections of particulate concentrations and temperature through the lake-breeze life cycle. The smaller suspended particulates (0.5–3.0 µm), which essentially float with the air, clearly suggest that a significant, fraction of the pollutants released from nearshore sources move inland within the inflow, rise aloft, at the front, advect lakeward in the return flow layer, and then sink back down into the inflow layer offshore. By contrast, larger particles (7–9 µm), having significant terminal velocities, fall out of the cell while over the lake and do not appear to take part in the recirculation phenomena. The role of continuous fumigation of plumes from elevated point sources is also discussed. A schematic model of the lake breeze and its effects on pollutant transport is presented.

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