A simple analytic model is constructed to elucidate some basic features of the response of the tropical atmosphere to diabatic heating. In particular, there is considerable east-west asymmetry which can be illustrated by solutions for heating concentrated in an area of finite extent. This is of more than academic interest because heating in practice tends to be concentrated in specific areas. For instance, a model with heating symmetric about the equator at Indonesian longitudes produces low-level easterly flow over the Pacific through propagation of Kelvin waves into the region. It also produces low-level westerly inflow over the Indian Ocean (but in a smaller region) because planetary waves propagate there. In the heating region itself the low-level flow is away from the equator as required by the vorticity equation. The return flow toward the equator is farther west because of planetary wave propagation, and so cyclonic flow is obtained around lows which form on the western margins of the heating zone. Another model solution with the heating displaced north of the equator provides a flow similar to the monsoon circulation of July and a simple model solution can also be found for heating concentrated along an inter-tropical convergence line.

Some simple solutions for heat-induced tropical circulation.

A coupled atmosphere-ocean model is developed and used to study the ENSO (El Ni&ntilde/Southern Oscillation) phenomenon. With no anomalous external forcing, the coupled model reproduces certain key features of the observed phenomenon. including the recurrence of warm events at irregular intervals with a preference for three to four years. It is shown that the mean sea surface temperature, wind and ocean current fields determine the characteristic spatial structure of ENSO anomalies. The tendency for phase-locking of anomalies is explained in terms of a variation in coupling strength associated with the annual cycle in the mean fields. Sensitivity studies reveal that both the amplitude and the time of scale of the oscillation are sensitive to several parameters that affect the strength of the atmosphere–ocean coupling. Stronger coupling implies larger oscillations with a longer time scale. A critical element of the model oscilliation is the variability in the equatorial heat content of the upper o...

A Model El Niño–Southern Oscillation

The single most prominent signal in year-to-year climate variability is the Southern Oscillation, which is associated with fluctuations in atmospheric pressure at sea level in the tropics, monsoon rainfall, and wintertime circulation over North America and other parts of the extratropics. Although meteorologists have known about the Southern Oscillation for more than a half-century, its relation to the oceanic El Nino phenomenon was not recognized until the late 1960's, and a theoretical understanding of these relations has begun to emerge only during the past few years. The past 18 months have been characterized by what is probably the most pronounced and certainly the best-documented El Nino/Southern Oscillation episode of the past century. In this review meteorological aspects of the time history of the 1982-1983 episode are described and compared with a composite based on six previous events between 1950 and 1975, and the impact of these new observations on theoretical interpretations of the event is discussed.

https://science.sciencemag.org/content/sci/222/4629/1195.full.pdf

Meteorological Aspects of the El Niño/Southern Oscillation

An analysis of 35-yr (1965–99) data reveals vital impacts of strong (but not moderate) El Nino and La Nina events on tropical storm (TS) activity over the western North Pacific (WNP). Although the total number of TSs formed in the entire WNP does not vary significantly from year to year, during El Nino summer and fall, the frequency of TS formation increases remarkably in the southeast quadrant (0°–17°N, 140°E–180°) and decreases in the northwest quadrant (17°–30°N, 120°–140°E). The July–September mean location of TS formation is 6° latitude lower, while that in October–December is 18° longitude eastward in the strong warm versus strong cold years. After the El Nino (La Nina), the early season (January–July) TS formation in the entire WNP is suppressed (enhanced). In strong warm (cold) years, the mean TS life span is about 7 (4) days, and the mean number of days of TS occurrence is 159 (84) days. During the fall of strong warm years, the number of TSs, which recurve northward across 35°N, is 2.5 ...

How Strong ENSO Events Affect Tropical Storm Activity over the Western North Pacific(.

Summary. The single most prominent signal in year-to-year climate variability is the Southern Oscillation, which is associated with fluctuations in atmospheric pressure at sea level in the tropics, monsoon rainfall, and wintertime circulation over North America and other parts of the extratropics. Although meteorologists have known about the Southern Oscillation for more than a half-century, its relation to the oceanic El Niio phenomenon was not recognized until the late 1960's, and a theoretical understanding of these relations has begun to emerge only during the past few years. The past 18 months have been characterized by what is probably the most pronounced and certainly the best-documented El Nino/Southern Oscillation episode of the past century. In this review meteorological aspects of the time history of the 1982-1983 episode are described and compared with a composite based on six previous events between 1950 and 1975, and the impact of these new observations on theoretical interpretations of the event is discussed. Summary. The single most prominent signal in year-to-year climate variability is the Southern Oscillation, which is associated with fluctuations in atmospheric pressure at sea level in the tropics, monsoon rainfall, and wintertime circulation over North America and other parts of the extratropics. Although meteorologists have known about the Southern Oscillation for more than a half-century, its relation to the oceanic El Niio phenomenon was not recognized until the late 1960's, and a theoretical understanding of these relations has begun to emerge only during the past few years. The past 18 months have been characterized by what is probably the most pronounced and certainly the best-documented El Nino/Southern Oscillation episode of the past century. In this review meteorological aspects of the time history of the 1982-1983 episode are described and compared with a composite based on six previous events between 1950 and 1975, and the impact of these new observations on theoretical interpretations of the event is discussed.

Meteorological Aspects of the El Nifio/Southern Oscillation

Thunderstorm frequency and amount of moisture above 500 mb. both indicate that the equatorial regions of South America and Africa and the “maritime continent” of Indonesia and the Carolines generate a much greater amount of heat for export than do equatorial oceanic regions. Over the maritime continent in January 1963, heat generated from excessive rains was efficiently transported northward and through conversion of potential to kinetic energy proably helped maintain an intense subtropical jet stream. In January 1964 drought over the maritime continent was accompained by a relative accumulation of heat in the upper troposphere, associated with inefficient poleward transport, and a much weaker circulation. Most winters over the western Pacific and southeast Asia fluctuate between situations typical of January 1963 and January 1964. Since the troposphere over the maritime continent in winter is probably the single greatest source of energy for the extratropical circulation, the proposed Marshall I...

Role of a tropical “maritime continent” in the atmospheric circulation1

In the eastern tropical Pacific, where the phenomenon of El Nino is best developed, the atmospheric circulation undergoes a marked annual cycle as well. Analysis of data from a recently compiled atlas elucidates the role of the annual cycle in modifying the great 1972–73 Nino, and confirms that off South America upwelling and sea surface temperature are not directly linked. Meridional profiles derived from the atlas reveal that oceanic heat loss to the air is a function of wind speed rather than of sea surface temperature and that rainfall can be accounted for in terms of the horizontal convergence of moisture. Distribution of tropical cyclones is not significantly related to El Nino, while predicting El Nino has proved much more difficult than had been expected.

Meteorological Aspects of El Niño

Parameterizations in numerical models of the general atmospheric circulation accord with the hypothesis advanced by lchiye and Petersen and Bjerknes—high sea surface temperatures “cause” high local rainfall. Observations at Canton Island and elsewhere in the tropics fail to support this attractively simple idea.

Sea Surface Temperature and Local Weather

Except for parts of the northwest Pacific, Indian Ocean and Pacific Ocean hurricanes always begin to develop in troughs located at high enough latitudes for low-level westerly winds to be observed on their equatorial sides. These near-equatorial troughs coincide with axes of maximum sea surface temperature, and in this respect they resemble continental heat troughs. Oceanic near-equatorial troughs follow the march of the sun. Generally, the farther they are from the equator the more often do hurricanes begin to form in them. The meridional rate of trough movement depends on the rate of ocean surface heating. Seas east and equatorward of the continents. Through the spring, continental heating rapidly diminishes the equatorward winds of winter, reducing evaporational cooling of the sea surface and mixed-layer depth. The consequent sea surface temperature rise brings the near-equatorial troughs poleward and starts the hurricane season only. In the height of summer, monsoon winds by increasing evapor...

C. S. Ramage

Papers

Role of a tropical “maritime continent” in the atmospheric circulation1

Meteorological Aspects of El Niño

Sea Surface Temperature and Local Weather

Monsoonal Influences on the Annual Variation of Tropical Cyclone Development over the Indian and Pacific Oceans