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The North Atlantic Oscillation (NAO) and Southern Oscillation (SO) are compared from the standpoint of their association with Northern Hemisphere winter mean distributions of sea-level pressure (SLP) and 500 mb height. The NAO and SO are associated with significant SLP differences over much of the hemisphere except for Siberia and western North America. Significant SLP and 500 mb height differences occur in the NAO over the Atlantic Ocean and near Baja California, while in the SO they occur over the Pacific Ocean, India and the western Atlantic. Only over the latter region do large pressure and height variations consistently occur in the extremes of both oscillations; these are also associated with winter temperature variability over the southeastern United States. For example, during winter 1982–83, when the two oscillations simultaneously reached extremes, the NAO was associated with record December warmth east of the Mississippi River, but during January and February the SO dominated the heigh...

Quasi-biennial and long-term fluctuations in the latitude, longitude and pressure of the Azores High, Pacific High, Icelandic Low, and Aleutian Low have been determined for the period 1899–1967. Within the quasi-biennial framework, an increase in pressure of the Azores High is associated with an increase in pressure of the Pacific High and Aleutian Low, but a decrease in pressure of the Icelandic Low. Based on data for the period 1951–1967, there is a significant tendency for the Azores High to be relatively far west, and the pressure relatively low, at the time of quasi-biennial west wind maximum in the low tropical stratosphere, and for the Pacific High to be relatively far south at this same time. The latter appears in agreement with the finding that the centroid of the north polar vortex is displaced farther toward the Pacific Ocean at the time of quasi-biennial west wind maximum. The most impressive long-term trends are the indicated 5° latitude northward displacement of the Pacific High and...

The GISS general circulation model was used to compute global monthly mean forecasts for January 1973, 1974, and 1975 from initial conditions on the first day of each month and constant sea surface temperatures. Forecasts were evaluated in terms of global and hemispheric energetics, zonally averaged meridional and vertical profiles, forecast error statistics, and monthly mean synoptic fields. Although it generated a realistic mean meridional structure, the model did not adequately reproduce the observed interannual variations in the large scale monthly mean energetics and zonally averaged circulation. The monthly mean sea level pressure field was not predicted satisfactorily, but annual changes in the Icelandic low were simulated. The impact of temporal sea surface temperature variations on the forecasts was investigated by comparing two parallel forecasts for January 1974, one using climatological ocean temperatures and the other observed daily ocean temperatures. The use of daily updated sea surface temperatures produced no discernible beneficial effect.

We have investigated the well-known tendency for winter temperatures to be low over northern Europe when they are high over Greenland and the Canadian Arctic, and conversely. Well-defined pressure anomalies over most of the Northern Hemisphere are associated with this regional seesaw in temperature, and these pressure anomalies are so distributed that the pressure in the region of the Icelandic low is negatively correlated with the pressure over the North Pacific Ocean and over the area south of 50°N in the North Atlantic Ocean, Mediterranean and Middle East, but positively correlated with the pressure over the Rocky Mountains. The composite patterns of pressure anomalies in the seesaw are almost identical to the fist eigenvector in the monthly mean pressure, but the standard deviations of pressure anomalies in seesaw mouths are as large as the standard deviations of monthly means in general. Since 1840 the seesaw, as defined by temperatures in Scandinavia and Greenland, occurred in more than 40%...

Contemporaneous correlations between geopotential heights on a given pressure surface at widely separated points on earth, referred to as teleconnections in this paper, are studied in an attempt to identify and document recurrent spatial patterns which might be indicative of standing oscillations in the planetary waves during the Northern Hemisphere winter, with time scales on the order of a month or longer. A review of existing literature on the subject reveals the existence of at least four such patterns: the North Atlantic and North Pacific Oscillations identified by Walker and Bliss (1932). a zonally symmetric seesaw between sea level pressures in polar and temperature latitudes, first noted by Lorenz (1951), and what we will refer to as the Pacific/North American pattern, which has been known to operational long-range forecasters in this country since the 1950's. A data set consisting of NMC monthly mean sea level pressure and 500 mb height analyses for a 15-year period is used as a basis fo...

The average latitude, longitude and central pressure of the four centers of action (Icelandic low, Aleutian low, Azores high, Pacific high) have been estimated for each of the 80 years of the Northern Hemisphere Historical Weather Map Series (1899–1978), and compared with year-average values of Northern Hemisphere surface temperature (NHST) and sea surface temperature (SST) in the region 0–10°S, 180–90°W of the equatorial eastern Pacific. Inasmuch as NHST and SST have been positively correlated during the 80-year period, their relations with the centers of action have been estimated using partial correlation coefficients. While there has been a tendency for northward displacement of all four centers of action at time of hemispheric warming, none of the partial correlations is significant at the 95% level, taking into account the serial correlation of the data. However, the correlation (r) of 0.31 in the case of the Aleutian low is on the verge of significance, and the correlation of 0.33 in the c...

Orthogonally rotated principle component analysis (RPCA) of Northern Hemisphere 1-month mean 700 mb heights is used to identify and describe the seasonality and persistence of the major modes of interannual variability. The analysis is detailed and comprehensive, in that 1) a high resolution, approximately equal-area 358-point grid is used for the virtually maximum possible 35-year period of record, 2) a positive bias in the NMC data base in the early 1950s in the subtropics is largely eliminated for the first time, and 3) homogeneous, separate analyses of each month of the year are carried out, detailing the mouth-to-month changes in the dominant circulation patterns. Winter results are similar to those of other recent RPCA and teleconnection studies except that some less obvious patterns are identified and further detail of the better-known patterns is provided. Two north-south dipole patterns are found over the Pacific Ocean (West Pacific Oscillation and East Pacific pattern) and over the Atla...

The precipitation over northern Honduras in December was significantly correlated with 700 mb heights over Valencia, Ireland. (Measurements at Valencia were used to represent a more accurate indicator of the variations in the Icelandic Low than interpolated analyses in the Low over the Atlantic Ocean.) This relationship was suggested by a comparison between observed and theoretical “wave-trains” in the 700 mb height field. The observed 700 mb height wave train over the Atlantic was related to anomalies in the sea-surface temperature (SST) over the tropical Pacific Ocean; therefore, the northern Honduran rainfall was also significantly correlated with the tropical Pacific SST.