Atmospheric circulation cells associated with the El Nino–Southern Oscillation (ENSO) are described and examined using the NCEP–NCAR reanalysis field and the NCEP sea surface temperature (SST) from January 1950 to December 1999. The divergent wind and pressure vertical velocity are employed for the identification of atmospheric circulation cells. The warm phase of ENSO shows positive SST anomalies in the equatorial eastern Pacific and along the east coast of Asia and the west coast of North America, and negative SST anomalies in the off-equatorial western Pacific and in the central North Pacific. Associated with this SST anomaly distribution are variations of atmospheric zonal and meridional circulation cells over the Pacific. The equatorial zonal Walker circulation cell is weakened, consistent with previous schematic diagrams. The anomalous meridional Hadley circulation cell in the eastern Pacific shows the air rising in the Tropics, flowing poleward in the upper troposphere, sinking in the subt...

Atmospheric Circulation Cells Associated with the El Niño–Southern Oscillation

In order to produce gridded fields of pollutant concentration data and surface wind data for use in an air quality model, a number of techniques for interpolating sparse data values are compared. The techniques are compared using three data sets. One is an idealized concentration distribution to which the exact solution is known, the second is a potential flow field, while the third consists of surface ozone concentrations measured in the Los Angeles Basin on a particular day. The results of the study indicate that fitting a second-degree polynomial to each subregion (triangle) in the plane with each data point weighted according to its distance from the subregion provides a good compromise between accuracy and computational cost.

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A Comparison of Interpolation Methods for Sparse Data: Application to Wind and Concentration Fields

Phenomena important for Atlantic climate variability include the Atlantic zonal equatorial mode, the tropical Atlantic meridional gradient mode, and the North Atlantic Oscillation (NAO). These climate phenomena and their associated atmospheric circulation cells are described and discussed using the NCEP–NCAR reanalysis field and the NCEP sea surface temperature (SST) from January 1950 to December 1999. Atmospheric divergent wind and vertical motion are used for the identification of atmospheric circulation cells. During the peak phase of the Atlantic equatorial mode, the Atlantic Walker circulation weakens and extends eastward, which results in surface westerly wind anomalies in the equatorial western Atlantic. These westerly wind anomalies are partly responsible for warming in the equatorial eastern Atlantic that occurs in the second half of the year. The Atlantic equatorial mode involves a positive ocean–atmosphere feedback associated with the Atlantic Walker circulation, similar to the Pacific...

Atlantic Climate Variability and Its Associated Atmospheric Circulation Cells

Variability of the tropical Western Hemisphere warm pool (WHWP) of water warmer than 28.5°C, which extends seasonally over parts of the eastern North Pacific, the Gulf of Mexico, the Caribbean, and the western tropical North Atlantic (TNA), was previously studied by Wang and Enfield using the da Silva data from 1945–93. Using additional datasets of the NCEP–NCAR reanalysis field and the NCEP SST from 1950–99, and the Levitus climatological subsurface temperature, the present paper confirms and extends the previous study of Wang and Enfield. The WHWP alternates with northern South America as the seasonal heating source for the Walker and Hadley circulations in the Western Hemisphere. During the boreal winter a strong Hadley cell emanates northward from the Amazon heat source with subsidence over the subtropical North Atlantic north of 20°N, sustaining a strong North Atlantic anticyclone and associated northeast (NE) trade winds over its southern limb in the TNA. This circulation, including the NE ...

A Further Study of the Tropical Western Hemisphere Warm Pool

This chapter describes and discusses the Walker and Hadley circulations associated with the El Nino/Southern Oscillation (ENSO), the Atlantic “Nino”, the tropical Atlantic meridional gradient variability, the Western Hemisphere warm pool (WHWP), and the North Atlantic Oscillation (NAO). During the warm phase of ENSO, the Pacific Walker circulation, the western Pacific Hadley circulation, and the Atlantic Hadley circulation are observed to be weakened, whereas the eastern Pacific Hadley circulation is strengthened. During the peak phase of the Atlantic Nino, the Atlantic Walker circulation weakens and extends eastward and the Atlantic Hadley circulation strengthens. The tropical Atlantic meridional gradient variability corresponds to a meridional circulation in which the air rises over the warm sea surface temperature (SST) anomaly region, flows toward the cold SST anomaly region aloft, sinks in the cold SST anomaly region, then crosses the equator toward the warm SST region in the lower troposphere. During periods when the NAO index is high, the atmospheric Ferrei and Hadley circulations are strengthened, consistent with surface westerly and easterly wind anomalies in the North Atlantic and in the middle to tropical Atlantic, respectively. The chapter also discusses a tropo-spheric bridge by the Walker/Hadley circulation that links the Pacific El Nino with warming of the tropical North Atlantic (TNA) and the WHWP.

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ENSO, Atlantic Climate Variability, and the Walker and Hadley Circulations

Long term regional patterns and transfrontier exchanges of airborne sulfur pollution in Europe

This study describes objective analysis of the atmospheric conditions that precede or accompany severe thunderstorms and tornadoes. The data used are standard rawinsonde observations and hourly surface reports as they are transmitted over teletypewriter. In analyzing upper air data, spherical coordinates are used with grid points 2½° of lat. and long. apart. Hourly observations are analyzed on a 1¼° grid. The vertical structure of the atmosphere is represented by seven layers between the surface and 100 mb. Observational data are averaged for these layers using all points in the soundings. By use of a nondimensional pressure term as the vertical coordinate, the three layers below 500 mb. slope with the terrain, and the lowest layer contains most boundary processes. The objective analysis procedure fits a first degree polynomial to at least five observations that are nearest to a grid point. A distance weighting factor and upstream-downstream enhancement are used. The analysis method smooths the o...

Objective analysis of environmental conditions associated with severe thunderstorms and tornadoes1

A numerical procedure is described for computing a stream-function field from the vorticity of the horizontal wind field. The method was developed for use in meteorological studies which require analyses based solely on wind observations, or for use in the construction of balanced fields of winds and heights. The boundary of the net region is treated by specifying the gradients of the stream function normal to the boundary. The solution for the stream-function field is achieved relatively quickly by the iterative process known as the implicit alternating-direction method. The same procedure is also used to calculate a velocity-potential field from the divergence of the wind field. The computations are performed on a spherical net and have been tested on wind fields over both the United States and the Caribbean. The computed stream-function fields have been found to provide reliable and sufficiently accurate representations of the non-divergent wind field.

A Numerical Procedure for Computing Fields of Stream Function and Velocity Potential

The probability is determined that an aircraft will encounter moderate or severe high-level turbulence during a 100-mi. flight segment when particular values of certain meteorological quantities exist in that locality. The turbulence data used are pilot reports collected by the U.S. Weather Bureau Clear Air Turbulence Project, for March 12–24, 1962 and February 4–9, 1963. The meteorological quantities which were computed from standard data include vertical vector wind shear, vertical wind direction shear, temperature lapse rate, horizontal wind shear, vorticity, and resultant deformation. A correlation of 0.45 was found between turbulence frequency and the product of vertical vector wind shear and deformation. This value is the highest correlation found so far with data of this type. The product of wind shear and deformation is an important factor in the development of fronts. One might expect that a tendency for frontogenesis would correlate better with turbulence than would frontolysis. The dat...

Robert L. Mancuso

Papers

Long term regional patterns and transfrontier exchanges of airborne sulfur pollution in Europe

Objective analysis of environmental conditions associated with severe thunderstorms and tornadoes1

A Numerical Procedure for Computing Fields of Stream Function and Velocity Potential

Clear air turbulence frequency as a function of wind shear and deformation1

A practical and economic method for estimating wind characteristics at potential wind energy conversion sites