Sea Level Pressure Maps Research Articles

Sensitivity of ECMWF Analyses-Forecasts of Tropical Cyclones to Cumulus Parameterization

Abstract The sensitivity of the ECMWF analysis-forecast system for four tropical cyclones during the period spanned by the Australian Monsoon Experiment to cumulus parameterization and model resolution is presented. Two parameterization schemes were compared: namely, the Kuo cumulus parameterization and the Betts-Miller adjustment scheme. Both analyses and forecasts show considerable sensitivity with the Betts-Miller scheme generating more intense cyclonic systems as indicated by maps of sea-level pressure, low-level winds, vorticities, and cross sections in the neighborhood of the cyclones. The Betts-Miller scheme also results in better consistency of the fields in the vertical between the divergent circulation and vertical velocity. Of the two cases considered, one (for tropical cyclone Jason) showed a marked sensitivity to increased model resolution with the higher resolution forecast showing considerable improvement.

An objective method for computing advective surface velocities from sequential infrared satellite images

Using cross correlations between sequential infrared satellite images, an objective technique is developed to compute advective sea surface velocities. Cross correlations are computed in 32 × 32 pixel search (second image) and 22 × 22 template (first image) windows from gradients of sea surface temperature computed from the satellite images. Velocity vectors, computed from sequential images of the British Columbia coastal ocean, generally appear coherent and consistent with the seasonal surface current in the region. During periods of strong wind forcing, as indicated by maps of sea level pressure, the image advective velocities are stronger and more coherent spatially and appear to cross surface temperature gradients; when winds are weaker, the advective velocities correspond better with the infrared temperature patterns, suggesting the increased contribution of the geostrophic current to the surface flow. Velocities determined from coincident, near‐surface drogued (5–10 m) buoys, positioned every half hour by internal LORAN‐C units in mid‐June, show excellent agreement with the image advective velocities. In addition, conductivity, temperature, and depth (CTD) measurements (taken during the buoy tracking) confirm the homogeneity of the upper 10 m, and CTD‐derived geostrophic currents are consistent with both buoy and sequential image displacement velocities.

On Modes of Tropical Circulation and Climate Anomalies

Abstract Large-scale departure maps of sea level pressure (SLP) and sea surface temperature (SST) are presented for the tropical Atlantic and eastern Pacific Oceans, as obtained by stratification with respect to extreme climatic events in key regions of the tropical Americas. Drought in the Central American-Caribbean region is characterized by an equatorward expansion of the North Atlantic high, a band of anomalously cold water extending across the North Atlantic and a positive SST anomaly in the eastern Pacific. Drought in northeast Brazil is associated with high SLP over the South Atlantic and low SLP over the North Atlantic, cold water in the South Atlantic, a band of positive SST anomalies across the North Atlantic, and positive SST departures in the eastern Pacific. During the Ecuador/Peru El Nino, SLP in the eastern Pacific is low and SST high, and positive SLP departures dominate the tropical Atlantic. Independently, preferred modes of departure configurations are identified from principal compone...

The Pacific El Niño Phenomenon and the Atlantic Circulation

Abstract Atmospheric–oceanic departure patterns in the tropical Atlantic and eastern Pacific associated with the Ecuador/Peru El Ninno and its antithesis are studied on the basis of long-term ship observations during 1911–71. Departure maps of sea level pressure (SLP), wind speed and sea surface temperature (SST) in March/April are presented for composite of ten extreme years of either regime. The evolution of SLP anomalies from the preceding to the event year is traced for large ocean areas. Gaussian and binomial probabilities are calculated as a measure of the importance of SLP departures. El Nino years are characterized by abnormally low SLP over the eastern South Pacific and positive SLP anomalies over the Atlantic; winds are weaker than normal over the Pacific, and stronger over the Atlantic; SST anomalies are positive in the Pacific, but negative in a band of the Atlantic extending from West Africa toward the South American coast. During counter-El Nino years, departure patterns am approximately inv...

Prediction of Meteorological Factors Related to Beach Erosion at New Jersey and Long Island, N. Y.

Abstract Prediction of meteorological factors related to storm-caused beach erosion are discussed. Composite sea level pressure maps are presented for beach erosion events that occurred on the New Jersey and Long Island, New York, coasts. Significant meteorological conditions related to beach erosion are: 1) an angle between the predominant wind direction on the eroding beach and the orientation of the smoothed coastline of between 0° and 20° for Long Island, and between 20° and 40° for New Jersey; 2) a setup period of at least 18 h during which coastal winds do not vary more than 20° from the observed predominant wind direction; 3) at some time during the setup period the wind direction upstream for a distance at least 550 km does not vary more than 20° from the coastal wind direction; and 4) the upwind surface pressure gradient at some time during the setup period attains a value of at least 4 mb (200 km)−1

Some Effects of Surface Anomalies in a Global General Circulation Model1

The Mintz-Arakawa two-level general circulation model has been used in a series of experiments to compute the response of the atmosphere to certain persistent sea-surface temperature anomalies and to changes in the position of the continental Northern Hemisphere snow line over periods up to 90 days. Results are shown in terms of differences between anomaly and control histories are revealed by global, 30-day mean sea-level pressure maps, and time series of three regional indices of synoptic activity. The experiments show significant interhemispheric effects after about 1 month, phase shifts of 1 to 2 weeks in major cyclone developments, stronger reactions to sea-temperature anomalies in winter than in summer, and marked influence of the snow line on the winter monsoonal pressure difference between the continents and the North Atlantic Ocean.

LARGE-SCALE FEATURES OF MONTHLY MEAN NORTHERN HEMISPHERE ANOMALY MAPS OF SEA-LEVEL PRESSURE

Spatial patterns of circulation variability over the Northern Hemisphere and their changes during the past 70 yr (1899–1969) are examined using eigenvector analyses of mean January and July sea-level pressure maps. The first several eigenvectors display variability associated with the major centers of action (the subpolar oceanic Lows, the subtropical oceanic Highs, the winter Siberian High, and the summer Asiatic Low). The pattern of the first eigenvector of January suggests that the intensity and latitudinal position of the major circulation features over the North Atlantic are associated with the intensity and position of the Aleutian Low over the North Pacific. The time series of the coefficients of the hemispheric eigenvectors are used to identify intervals of change in the hemispheric circulation associated with features on the scale of thc major centers of action. These time series provide a more general description of circulation change than that obtained from local or regional indices; but at the same time, they provide more detailed information than time series of hemispherically averaged indices. Two intervals of change in the large-scale hemispheric circulation are identified: the early to mid-1920s and the early to mid-1950s. Of the three periods separated by these two intervals of change, maximum contrast is noted between the first and third. For January, the strongest circulation features are found in the North Atlantic and European sectors in the first (earliest) period and in the North Pacific and Asian sectors in the third (latest) period.