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E. Paul McClain

Abstract

Revised means, frequency distributions and other statistics based on ten years of January temperature observations at the 200-, 100- and 50-mb levels are presented for four arctic stations. The frequency distributions are shown to be markedly bimodal, a characteristic that becomes more pronounced with increasing height and latitude. Thermal conditions in the arctic and antarctic stratospheres are compared with the aid of recent IGY data.

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E. Paul McClain

Some important European and American foehn research is reviewed briefly. A single winter chinook situation is analyzed in some detail using surface and upper-air synoptic data. Surface chinook winds in Montana are traced back westward and found over the Great Basin area in the middle troposphere. Qualitative evidence is found of ascent in the middle and upper troposphere above the descending foehn current. High- and low-level chinooks are differentiated, and the properties of chinook air are discussed.

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E. Paul McClain

Abstract

Some effects of the western mountain complex of North America on cyclones are investigated from the standpoint of how the vorticity tendency field might be influenced by orographically-induced vertical motion and divergence. A detailed case study is presented which includes computations of terms in the vorticity tendency equation during a lee cyclogenesis. The local increases in low-level vorticity which occurred during formation of the lee trough and cyclone were primarily due to horizontal convergence, while the horizontal and vertical advection of vorticity opposed the increases; the contribution of the tipping term was generally negligible. The study also provides evidence that orographic effects are insufficient to explain the genesis of major cyclonic storms.

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E. Paul McClain

Abstract

No Abstract Available.

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E. Paul McClain

Abstract

A previous study by the author of January temperatures in the mid-stratosphere at several arctic stations near 80W has been extended to include stations in other sectors of the Arctic and the additional months of December and February. Distinctly bimodal temperature frequency distributions are evidently confined to the general area of the Canadian Archipelago and northern Greenland, and are characteristic of this region throughout the winter. Mean 25-mb charts and mean cross-sections are used to illustrate two quite dissimilar thermal and circulation regimes that tend to dominate the arctic stratosphere for long periods during the polar night.

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Alan E. Strong and E. Paul McClain

Multi-window infrared measurements, together with visual channel observations, enable relatively high-resolution and accurate local, regional, and global retrievals of ocean surface temperatures to be repetitively and routinely obtained from operational environmental satellites. Drifting buoys appear to be the best means to date of validating the satellite estimates. Root mean square differences of about 0.6°C are found between satellite and drifter, whereas with ships-of-opportunity they are 1.8°C. Fixed buoy comparisons fall between these extremes.

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E. PAUL McCLAIN and ALAN E. STRONG

Abstract

Irregularities in sea-surface sunglint patterns have been frequently noticed in photographs from earth-orbiting satellites. High-resolution color photographs from low-altitude manned spacecraft missions have shown small-scale detail in many of the sunglint pictures. At the much higher altitude of the Applications Technology Satellites (ATS) the reflection pattern of the sun is spread over such a large area that varying sea-surface conditions can be inferred in many areas within a single sunglint region.

Of particular interest are patches or swaths of ocean surface that appear dark within the brighter sunglint region. Short-period time sequences of photographs from ATS III exhibit reversals in brightness when the horizontal specular point moves into the area of the anomalous dark feature.

Modeling statistics of sea-surface slope for increasing near-surface wind velocities show 1) a rapid drop in maximum sunglint radiance and 2) an increase in the area covered by the total glint pattern. It is shown, by combining calm surface conditions with higher background sea states, that sunglint patterns can be obtained which are very similar to those observed from satellites. Consequently, anomalous dark swath observations from ESSA satellites can be used to infer sea-state variations. The streaklike anomalies in many cases correspond to calm waters beneath high-pressure ridges or, when paralleling coastlines, the seaward limit of local sea-breeze circulations.

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E. Paul McClain and Edwin F. Danielsen

Abstract

The thermal structure of the troposphere and lower stratosphere during the movement eastward of several Pacific troughs is examined primarily from the standpoint of the distribution of baroclinity within a vertical plane extending across the northwestern and north central United States. Baroclinity is defined and then expressed in a form suitable to the potential-temperature cross-sections employed in this study. Dominating features of the thermal field are two types of baroclinic zones: (1) broad and essentially non-frontal zones which form the leading and trailing edges of deep, rapidly moving cold domes in the middle and upper troposphere; (2) narrow, frontal type zones comprising the leading or trailing edges of either slowly-moving, low-level cold domes or rapidly-moving, upper-level ones. There is evidence that the non-frontal baroclinic zones are equally as important, both dynamically and synoptically, as the frontal ones.

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Larry L. Stowe, Paul A. Davis, and E. Paul McClain

Abstract

An algorithm for the remote sensing of global cloud cover using multispectral radiance measurements from the Advanced Very High Resolution Radiometer (AVHRR) on board National Oceanic and Atmospheric Administration (NOAA) polar-orbiting satellites has been developed. The CLAVR-1 (Clouds from AVHRR-Phase I) algorithm classifies 2 × 2 pixel arrays from the Global Area Coverage (GAC) 4-km-resolution archived database into CLEAR, MIXED, and CLOUDY categories. The algorithm uses a sequence of multispectral contrast, spectral, and spatial signature threshold tests to perform the classification. The various tests and the derivation of their thresholds are presented. CLAVR-1 has evolved through experience in applying it to real-time NOAA-11 data, and retrospectively through the NOAA AVHRR Pathfinder Atmosphere project, where 16 years of data have been reprocessed into cloud, radiation budget, and aerosol climatologies. The classifications are evaluated regionally with image analysis, and it is concluded that the algorithm does well at classifying perfectly clear pixel arrays, except at high latitudes in their winter seasons. It also has difficulties with classifications over some desert and mountainous regions and when viewing regions of ocean specular reflection. Generally, the CLAVR-1 fractional cloud amounts, when computed using a statistically equivalent spatial coherence method, agree to within about 0.05–0.10 of image/analyst estimates on average. There is a tendency for CLAVR-1 to underestimate cloud amount when it is large and to overestimate it when small.

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ALAN E. STRONG, E. PAUL McCLAIN, and DAVID F. McGlNNlS

Abstract

A case is made for the detection of melting snow or ice using multispectral remote sensing from earth satellites. Snow and thick ice are highly reflective in both the visible and the near-infrared portions of the electromagnetic spectrum. During thaw conditions, however, near-infrared radiation is absorbed strongly, while reflection of visible radiation is only slightly affected. Simultaneous visible and near-infrared imagery from the Nimbus 3 satellite illustrates how these reflectance differenecs can be used to obtain information of hydrologic usefulness. Two examples of such use are presented.

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