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Jay S. Winston and Lloyd Tourville

The cloud structure of an occluded cyclone and its environs over the Gulf of Alaska is revealed in detail by a series of TIROS pictures. The pictures clearly portray:

  • (1) the nature and extent of dense cloudiness around the inner core of the cyclone;
  • (2) a broad band of cloudiness associated with the main polar front;
  • (3) the pattern of overrunning cloudiness marking a newly developing wave south of the main storm;
  • (4) a previously undetected, old cyclonic vortex in mid-troposphere; and
  • (5) the striking cellular arrangement of cumuliform clouds in the cyclonic flow to the rear of the storm.

These features are related to the conventional meteorological data and analyses over this area and are found in many places to corroborate them rather well. On the other hand, there are several places, particularly in view of the sparsity of conventional data, where the cloud pictures suggest that improvements could be made in the map analyses and numerically computed vertical motions on the basis of the TIROS cloud information.

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JAY S. WINSTON and P. KRISHNA RAO

Abstract

Daily composite Northern Hemisphere charts of outgoing long-wave radiation were derived from TIROS II measurements for about 25 days in late November and December 1960. Although data coverage was incomplete and variable each day, both latitudinal and overall daily averages of long-wave radiation were obtained. Large-scale temporal variations in the long-wave radiation are observed and are found to be generally related to temporal variations in kinetic and available potential energy over the Northern Hemisphere. Examination of the radiation latitudinally for various stages of an energy cycle that occurred at this time shows that the outgoing radiation, particularly at lower latitudes, decreased as westerly flow increased at lower latitudes. An average latitudinal profile of the TIROS long-wave data for all days studied shows rather good agreement with previous estimates made by investigators of the atmospheric heat budget.

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Eugene J. Aubert and Jay S. Winston

Abstract

By a study of heat sources and sinks, an attempt is made to further the knowledge of energy changes associated with the general circulation. The average monthly heating and cooling of the air between sea level and 10,000 ft is computed for individual and normal months. The heating and cooling regions show sizeable departures from normal and considerable monthly variations, both in magnitude and location. The absolute magnitudes of heating and cooling are greater in the colder seasons and at middle and high latitudes. At low latitudes, where the magnitudes are small, adiabatic motions are predominant. Attempts are made to determine the contributions of the various heat-exchange processes to the net heating. Certain relationships between the heating fields and the lO,OOO-ft monthly mean jet-stream are presented. The jet axis is usually found in the region of maximum transition of the heating field, with heating to the north and cooling to the south. Heat energy and kinetic energy appear to reach their longitudinal maxima at the same location along the jet.

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Arthur F. Kruger and Jay S. Winston

Abstract

The authors have been monitoring the large-scale circulation over the tropics since 1968 through use of operational tropical wind analyses prepared by the National Meteorological Center. Seasonal and monthly anomaly charts of the tropical circulation at 700 and 200 mb have been prepared using four-year seasonal and monthly means as a preliminary “normal” A sequence of seasonal anomaly charts is used here to describe the highly anomalous tropical circulation during the northern summer of 1972 and its antecedents. During this season the trades were weaker than “normal” over most of the Pacific with both the North and South Pacific anticyclones displaced poleward. In the upper troposphere the anomalous flow was anticyclonic over the Central Pacific reflecting the weakness of the mid-oceanic troughs north and south of the equator. From the eastern Pacific eastward across the Atlantic, Africa, and the Indian Ocean the flow at upper levels north of the equator was westerly relative to normal, signifying a notable reduction in the strength of the summertime “monsoon” easterlies over Africa and the Indian Ocean. The evolution of these striking circulation anomalies from a substantially different initial state a year earlier and their association with sea-surface temperature variations over the equatorial Pacific are discussed.

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DONALD A. HAINES and JAY S. WINSTON

Abstract

Monthly mean values of meridional transport of sensible heat by the atmosphere in the layer 850-500 mb. over the Northern Hemisphere poleward from the subtropics are analyzed for a period of 3½ years. The latitudinal values of this transport exhibit an annual cycle which is characterized by a rapid buildup from August to November and a slightly less rapid decline from February to June. Dissimilarities among the transport patterns for the same calendar months in different years are generally small; however, the month of December has marked variability. The longitudinal makeup of heat transport across latitude 45° N. in the cold season is dominated by three contributing regions which are associated with two of the three major waves observed in monthly mean flow patterns. The most sharply defined region of contribution to the heat transport across latitude 45° N. is associated with cold air moving southward to the rear of the trough line along the east coast of Asia. At 60° N., however, pronounced heat transport zones are generally absent except for the occasional appearance of a maximum over the eastern Atlantic and western Europe.

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P. Krishna Rao and Jay S. Winston

Abstract

Several samples of infrared radiation measurements in the 8–13 micron water-vapor “window” made by TIROS II are studied in relation to conventionally observed information on pressure systems, cloudiness and temperature These cases demonstrate further the synoptic capabilities, as well as some of the limitations, of these data for cloud detection; determination of cloud-top height; and observation of spatial gradients and temporal changes in the temperature of water-, land-, and snow-covered surfaces.

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William H. Klein and Jay S. Winston

The movement of the Atlantic hurricane of September 11–20, 1947, into the Gulf of Mexico rather than up the Atlantic Coast, is attributed to dynamic anticyclogenesis over the eastern United States. An attempt is made to explain this anticyclogenesis by the transfer of energy downstream from the mid-Pacific at a rate considerably greater than the speed of individual air particles. The motion and change in intensity of 700 mb trough and ridge systems are discussed in terms of constant absolute vorticity, horizontal temperature advection, and the process of confluence. It is concluded that the large-scale features of the hemispheric circulation are of great importance for short-range, as well as for extended, weather forecasting.

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WILLIAM H. KLEIN and JAY S. WINSTON

Abstract

The geographical frequencies of occurrence of troughs and ridges on both 5-day and 30-day mean 700-mb. charts for the Northern Hemisphere during a long period of record are presented for individual months. Many regions of maximum and minimum frequency show a close relationship to trough and ridge positions on long-period mean, or normal 700-mb. charts. However, even a cursory inspection of these frequency charts shows that they yield considerably more information for both the practicing forecaster and the research worker than can be derived solely from normal maps. Preferred trough and ridge locations and their seasonal changes appear to be related largely to land-sea boundaries with their associated thermal influences and also to prominent orography.

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JAY S. WINSTON and P. KRISHNA RAO

Abstract

Daily composite charts of outgoing long-wave radiation between latitudes 55°N. and 55°S. were derived from TIROS II measurements for 26 days between late November 1960 and early January 1961. Samples of these charts reveal the wealth of information available about the radiation patterns over the earth and about the synoptic distributions of the major cloud fields. Mean maps of outgoing long-wave radiation for four periods of generally more abundant radiation data portray the broad-scale variations in the radiation pattern both geographically and in time. For the Northern Hemisphere these maps show how the long-wave radiation varied during some very large-scale changes in 700-mb. mean flow which were part of a remarkable energy, or index, cycle in this period. Most pronounced were the sharp decreases in outgoing radiation that accompanied the penetration of westerlies into the subtropics where anticyclones had prevailed previously. In the Southern Hemisphere some sizable temporal variations also occurred; these appeared to be representative of a change in circulation from a zonal to a more meridional type. Average latitudinal profiles of the outgoing radiation for these four mean periods and for the entire 26 days are also presented. The overall distribution shows maxima of outgoing radiation near 20°N. and 20°S. with lower values toward higher latitudes in both hemispheres and in equatorial regions. Comparisons of these measurements from TIROS II with previous estimates of outgoing long-wave radiation by investigators of the heat budget show relatively good agreement.

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Arthur F. Krueger and Jay S. Winston

Abstract

The contrasting circulation and cloudiness over the tropics during two extremes of the zonally oriented Walker circulation are described. During February 1971 the trade winds over the Pacific Ocean were very strong with fast upper tropospheric westerlies superimposed. This was associated with well-developed, high-level oceanic troughs over the east central Pacific both north and south of the equator. Tropical convection was largely confined to the three tropical continental areas, while the ITCZ over the Pacific was very weak.

During February 1969 the Walker circulation was considerably weaker. Tropical convection was more extensive over the central and eastern Pacific. The high-level mid-oceanic troughs were also weaker and even replaced by weak anticyclonic flow over the convective regions. Associated with this the sub-tropical jet stream was very much stronger over the eastern Pacific, North America and the Atlantic, but weaker near Japan.

It is suggested that dynamic instability in the westerlies of the subtropical jet stream plays an important role in regulating the intensity of the tropical circulation.

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