North Pacific Sector Research Articles

Examples of Additionally Constrained Multiple Linear Regression

Abstract An additionally constrained multiple linear regression technique is outlined for use with the prediction or specification of fields of geophysical variables. The additional constraints are the requirement that the predictions or specifications have spatial interrelationships which are similar to the dominant empirical orthogonal functions of the dependent variables. Since the traditional multiple linear regression estimates by definition minimize the mean square errors for the data used to develop the model, the utility of the additional constraint can be evaluated only when the regression models are tested on new data. A so-called jackknife technique is used in this regard. This additionally constrained multiple linear regression technique is tested on two examples of the specification of monthly values using independent data for the same month. The first is the specification of North Pacific sector 700-mb geopotential heights using the time coefficients of the first two empirical orthogonal fun...

An estimate of average annual temperature variations for North America, 1602 to 1961

Annual surface temperature variations, 1602 to 1961, averaged over 77 United States and southwestern Canadian stations, are reconstructed from 65 aridsite tree-ring chronologies of western North America. Annual sea-level pressure reconstructions averaged over the North Pacific sector including North America and eastern Asia are inversely related to the temperature variations. Both the instrumental and reconstructed North American temperature averages are well correlated with Northern Hemisphere average temperatures during the early 20th-century warming but the correlation diminishes after the mid-1940s. The 1918 to 1947 interval is reconstructed to have been the warmest and 1877 to 1906 the coolest. The correlations between the temperature record and other high resolution temperature series from the Northern Hemisphere are generally insignificant. However, significant correlations are noted for certain 30-yr time periods. North American temperatures appear to have been out of phase with temperatures in Europe during the late 18th and early 19th centuries. Significant variations in the 30-yr mean temperatures are noted in several of the North American series. The warming early in the 20th century is the most marked followed by warming from 1717 to 1723 and from 1850 to 1866. Significant cooling occurs from 1810 to 1821 and from 1659 to 1669.

Large-scale hemispheric teleconnections with the frequency of tropical cyclone formation over the Northwest Pacific and North Atlantic Oceans

Large-scale circulation features during months with many and with few tropical cyclones revealed the following conditions: 1) With many typhoons in the northwest Pacific, a well-defined inter-tropical convergence zone (ITCZ) extended eastward to 160°E and was displaced to 20°N. At 200 mb an extensive anomalous anticyclonic circulation prevailed over the western and central Pacific. The circulation at 500 mb over Tibet was often characterized by an upper trough or a low-pressure region. Conditions characteristic of a break in the monsoon prevailed in India. The monsoon trough at 500 mb and at the surface over the Indian peninsula was relatively weak and was accompanied by higher-than-normal rainfall in the northern part of India and lower-than-normal rainfall over the peninsula. Furthermore, the polar vortex tended to be weak and moved away from the North Pacific sector. Finally, abnormally warm water was observed over the central and eastern Pacific and abnormally cold water over the West Pacific in summer as well as in the preceding spring. Sea surface temperatures (SST) in the region of the Kuroshio current and in the latitude belt 30°–40°N were also abnormally warm. subtropical high-pressure belt, displaced to the north; a deep Icelandic low; a stronger-than-normal polar vortex with a deep polar trough dipping far southward over the eastern part of the United States; a dominant high-pressure ridge over western Canada and the United States and a jet stream displaced northward over these regions. At 200 mb an anomalous anticyclonic circulation tends to prevail over the subtropical North Atlantic, with stronger-than-normal upper easterly flow in low latitudes. Positive sea surface temperature anomalies on a seasonal or long-term basis tend to be favorable for the formation of hurricanes.

Seasonal Climatic Anomaly Types for the North Pacific Sector and Western North America

Abstract Recurrent patterns of seasonal sea level pressure anomaly over the North Pacific sector and western North America are objectively identified using correlation coefficients between anomaly maps as a pattern recognition device. Five major anomaly type patterns are identified for each season. Each pressure anomaly type pattern is briefly discussed in terms of atmospheric circulation features and associated anomaly patterns of temperature and precipitation over the contiguous United States. Occurrences of each type pattern are analyzed in the time domain. Spring and summer types featuring below-normal pressures at high latitudes, associated with warm, dry conditions in the United States, occurred relatively often during the period of warm Northern Hemisphere temperatures from the mid-1920's to the mid-1950's. Types featuring above-normal pressure over high-latitude land area tended to occur frequently for all seasons during the period of relatively cool Northern Hemisphere temperatures prior to 1920....

Seasonal climatic anomaly types for the North Pacific sector and western North America : Blasing, T. J. and G. R. Lofgren, 1980. Mon. Weath. Rev., 108(6): 700–719

Seasonal climatic anomaly types for the North Pacific sector and western North America : Blasing, T. J. and G. R. Lofgren, 1980. Mon. Weath. Rev., 108(6): 700–719

Variations in climate since 1602 as reconstructed from tree rings

Spatial anomalies of tree-ring chronologies can provide information on high-frequency spatial anomalies in paleoclimate representing droughts, colder-than-normal intervals, and other synoptic-scale features. Examples are presented in which 65 tree-ring chronologies are calibrated with spatial anomalies in North American meteorological records of seasonal temperature and precipitation, and with sea-level pressure over the North American and North Pacific sectors. Multivariate transfer functions are obtained that scale and convert the past spatial variations in the tree-ring record into estimates of past variations in the meteorological record. Objective verifications of the reconstructions are obtained using independent meteorological observations for time periods other than those used in the calibration. Historical information or other proxy data from the 19th century are also used for verifying the decadal (or longer) and regional reconstructions and for identifying strengths and weaknesses of the various sources of information. The reconstructed winter and summer temperatures for the United States and southwestern Canada and winter precipitation for the Columbia Basin and California during the 17th through 19th centuries were found to differ from the 20th century means with large-scale variations evident. Extreme winters similar to 1976–1977 are also identified and found to be more frequent in the past, especially in the 17th century. The climatic reconstructions in this time domain are dominated by high-frequency, synoptic-scale fluctuations that can be interpreted as cyclonic-scale changes in atmospheric circulation. Such reconstructions may be useful for testing various climatic models and estimates developed primarily from 20th-century meteorological data against the longer estimated record for the 17th through 19th centuries.

Response of the NCAR General Circulation Model to Prescribed Changes in Ocean Surface Temperature Part I: Mid-Latitude Changes

Four numerical experiments are analyzed to determine the three-dimensional response of the NCAR general circulation model to large prescribed changes in mid-latitude North Pacific Ocean surface temperature. The ocean surface temperature (OST) boundary conditions are subjected to changes of opposite sign in the eastern and west-central portions of the North Pacific Ocean. The maximum amplitude of the temperature changes is either 12°C or 4°C. The model atmosphere response in the North Pacific sector includes changes in amplitude and vertical tilt of the long waves, an increased direct thermal circulation (i.e., warm air rises over the positive OST change and cold air sinks over the negative OST change), and locally enhanced westerlies to the north of the positive OST change. Cyclones form and/or intensify over the positive OST change and tend to be absent or weak over the negative OST change. The mid-tropospheric response extends downstream from the prescribed change region, and the response both over and downstream from the region depends strongly on the longitude of the prescribed changes. Many features of the response are statistically significant, although generally not over the continental United States. The amplitude and phase of the mid-tropospheric long waves (zonal wavenumbers 1–4) are also affected. The prescribed change response is largest and of greatest statistical significance when the prescribed change is very large (12°C maximum amplitude) but is also frequently detectable when the prescribed change is one-third as large (4°C maximum amplitude). A comparable experiment involving a prescribed North Atlantic OST change produces a similar mid-tropospheric response.

Reconstructing past climatic anomalies in the North Pacific and western North America from tree-ring data

Winter climatic anomalies in the North Pacific sector and western North America are statistically calibrated with tree-ring data in western North America and reconstructed back to AD 1700. The results are verified using climatic data from the last half of the 19th century, which is prior to the calibration period. Climatic conditions reconstructed for 18th and 19th century winters are then summarized and compared with the 20th century record.

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.