Showing papers in "Monthly Weather Review in 1982"
TL;DR: In this paper, the authors reviewed the necessary weighting factors for gridded data and the sampling errors incurred when too small a sample is available, and a rule of thumb indicating when an EOF is likely to be subject to large sampling fluctuations is presented.
Abstract: Empirical Orthogonal Functions (EOF's), eigenvectors of the spatial cross-covariance matrix of a meteorological field, are reviewed with special attention given to the necessary weighting factors for gridded data and the sampling errors incurred when too small a sample is available. The geographical shape of an EOF shows large intersample variability when its associated eigenvalue is “close” to a neighboring one. A rule of thumb indicating when an EOF is likely to be subject to large sampling fluctuations is presented. An explicit example, based on the statistics of the 500 mb geopotential height field, displays large intersample variability in the EOF's for sample sizes of a few hundred independent realizations, a size seldom exceeded by meteorological data sets.
2,793 citations
TL;DR: In this article, the evolution of sea surface temperature (SST) anomalies, surface wind fields, and precipitation anomaly patterns during major warm episodes in the eastern and central tropical Pacific are described in terms of composite SST and wind fields (30°N−30°S) for six warm episodes since 1949, and time series and cross-spectral analyses of mean monthly data along six shipping lanes which cross the equator between the South American coast and 170°W.
Abstract: Surface marine observations, satellite data, and station observations of surface pressure and precipitation are used to describe the evolution of sea surface temperature (SST) anomalies, surface wind fields, and precipitation anomaly patterns during major warm episodes in the eastern and central tropical Pacific. The sequence of events is described in terms of composite SST and wind fields (30°N–30°S) for six warm episodes since 1949, and time series and cross-spectral analyses of mean monthly data along six shipping lanes which cross the equator between the South American coast and 170°W. During the months preceding a warm episode, the equatorial easterlies are stronger than normal west of the dateline. This and other coherent and strongly developed anomaly patterns over the western equatorial Pacific and South Pacific are associated with a South Pacific Convergence Zone (SPCZ) located southwest of its normal position. During October-November prior to El Nino, the equatorial easterly anomalies i...
2,647 citations
TL;DR: In this paper, the effects of vertical wind shear and buoyancy on convective storm structure and evolution were investigated with the use of a three-dimensional numerical cloud model, by varying the magnitude of buoyant energy and one-directional vertical shear over a wide range of environmental conditions associated with severe storms.
Abstract: The effects of vertical wind shear and buoyancy on convective storm structure and evolution are investigated with the use of a three-dimensional numerical cloud model. By varying the magnitude of buoyant energy and one-directional vertical shear over a wide range of environmental conditions associated with severe storms, the model is able to produce a spectrum of storm types qualitatively similar to those observed in nature. These include short-lived single cells, certain types of multicells and rotating supercells. The relationship between wind shear and buoyancy is expressed in terms of a nondimensional convective parameter which delineates various regimes of storm structure and, in particular, suggests optimal conditions for the development of supercell type storms. Applications of this parameter to well-documented severe storm cases agree favorably with the model results, suggesting both the value of the model in studying these modes of convection as well as the value of this representation i...
1,157 citations
TL;DR: In this article, a technique is presented for selection of principal components for which the geophysical signal is greater than the level of noise, which is simulated by repeated sampling of principal component computed from a spatially and temporally uncorrected random process.
Abstract: A technique is presented for selection of principal components for which the geophysical signal is greater than the level of noise. The level of noise is simulated by repeated sampling of principal components computed from a spatially and temporally uncorrected random process. By contrasting the application of principal components based upon the covariance matrix and correlation matrix for a given data set of cyclone frequencies, it is shown that the former is more suitable to fitting data and locating the individual variables that represent large variance in the record, while the latter is more suitable for resolving spatial oscillations such as the movement of primary storm tracks.
440 citations
TL;DR: In this paper, the authors proposed a simple theory to explain how a veering environmental wind shear vector can cause an initially symmetric updraft to grow preferentially to the right of the wind vector and acquire cyclonic rotation.
Abstract: In the present investigation we propose a simple theory to explain how a veering environmental wind shear vector can cause an initially symmetric updraft to grow preferentially to the right of the shear vector and acquire cyclonic rotation. The explanation offered is based on linear theory which predicts that interaction of the mean shear with the updraft produces favorable vertical pressure gradients along its right flank. To asses the validity of linear theory for large-amplitude updrafts, the three-dimensional, shallow, anelastic equations are numerically integrated using a simple parameterization for latent heating within a cloud and the linear and nonlinear forcing terms are separately analyzed. These results suggest that although the nonlinear effects strongly promote splitting of the updraft, the linear forcing remains the dominant factor in preferentially enhancing updraft growth on the right flank. We believe this differential forcing is a major contributor to the observed predominance o...
397 citations
TL;DR: In this article, an extended empirical orthogonal function analysis technique is described which expands a data set in terms of functions which are the best representation of that data set for a sequence of time points.
Abstract: An extended empirical orthogonal function analysis technique is described which expands a data set in terms of functions which are the “best” representation of that data set for a sequence of time points. The method takes advantage of the fact that geophysical fields are often significantly correlated in both space and time. Two examples of applications of this technique are given which suggest it may be a highly useful tool for diagnosing the modes of variation of dominant sequences of events. In the first, an analysis of 300 mb relative vorticity, fairly regular advection of the major features of the spatial patterns is evident. Westward speeds of between 0.3 and 0.4 m s−1 are inferred. The second example illustrates extended functions of tropical Pacific Ocean surface temperatures. The dominant function, which is associated with El Nino, shows a high degree of persistence over a six-month sequence. The second most important function suggests opposing variations in the influences of the North a...
373 citations
TL;DR: In this paper, a horizontal roll detected in the reflectivity pattern resulting from airflow that is deflected upward by the ground, while carrying some of the smaller precipitation ahead of the main echo core of the squall line was detected.
Abstract: This paper presents the time-dependent analysis of the thunderstorm gust front with the use of Project NIMROD data. RHI cross sections of reflectivity and Doppler velocity are constructed to determine the entire vertical structure. The life cycle of the gust front is divided into four stages: (1) the formative stage; (2) the early mature stage; (3) the late mature stage; and (4) the dissipation stage. A new finding is a horizontal roll detected in the reflectivity pattern resulting from airflow that is deflected upward by the ground, while carrying some of the smaller precipitation ahead of the main echo core of the squall line. This feature is called a 'precipitation roll'. As determined from rawinsonde data, the cold air behind the gust front accounts for the observed surface pressure rise. Calculations confirm that the collision of two fluids produce a nonhydrostatic pressure at the leading edge of the outflow. The equation governing the propagation speed of a density current accurately predicts the movement of the gust front.
341 citations
TL;DR: In this paper, the authors present results of a comprehensive study of the relationship between the movement of tropical cyclones and the large-scale circulation which surrounds them in three ocean basins: the northwest Pacific, the west Atlantic and the Australian-South Pacific region.
Abstract: This paper presents results of a comprehensive study of the relationship between the movement of tropical cyclones and the large-scale circulation which surrounds them Cyclones have been stratified by direction and speed of movement, latitude, intensity change and size (as determined by the radius of the outermost closed surface isobar) in three ocean basins: the northwest Pacific, the west Atlantic and the Australian-South Pacific region Twenty-one different stratifications are available in the northwest Pacific, 13 in the west Atlantic and 6 in the Australian-South Pacific area Cyclone movement and surrounding flow relationships were studied at different pressure levels and a variety of radii Pressure-weighted layer-averages were also analyzed in search of such relationships Results show an important relationship between surrounding large-scale flow and tropical cyclone movement For all stratifications, the winds in the mid-troposphere (500–700 mb) at 5–7° latitude radius from the cyclone
339 citations
TL;DR: In this article, the spatial variability of mean sea level pressure and 500 mb height anomalies over the Southern Hemisphere during summer (DJF) and winter (JJA) was determined using eigenvector analysis based on daily synoptic maps from 1972 to 1979.
Abstract: The spatial variability of mean sea level pressure (SLP) and 500 mb height anomalies over the Southern Hemisphere during summer (DJF) and winter (JJA) is determined using eigenvector analysis based on daily synoptic maps from 1972 to 1979. The patterns of spatial distribution of pressure and height anomalies are further verified and examined by means of station data, and the eigenvectors are compared between the seasons and to those found for the Northern Hemisphere. The first eigenvector shows that midlatitude anomalies of SLP and 500 mb height are of an opposite sign to those found over and around Antarctica. The pattern is highly barotropic and suggests strengthening and weakening of the zonal wind in alternating latitude belts. The 500 mb height differences are calculated for five midlatitude to Antarctic station pairs using data from the late 1950's onward. These latitudinal height differences are also used to describe the association between the hemispheric westerlies and the Southern Oscil...
256 citations
TL;DR: In this paper, the authors extend the model of Charney and Straus (1980) to include an additional wave in the zonal direction which is highly baroclinically unstable and can interact directly with the externally forced large-scale wave.
Abstract: We hypothesize that periods of quasi-stationary behavior in the large scales are integrally associated with an organized behavior of the synoptic scales, thus the terminology “weather regime.” To investigate our hypothesis, we extend the model of Charney and Straus (1980) to include an additional wave in the zonal direction which is highly baroclinically unstable and can interact directly with the externally forced large-scale wave. We find that such a model aperiodically vacillates between two distinct weather regime states which are not located near any of the stationary equilibria of the large-scale state; thus, we cannot ascertain the qualitative behavior of the large-scale flow in our model knowing only the large-scale equilibria and their respective stabilities to perturbations on the scale of the equilibria. The state of the model flow may remain in either one of the two regime states for several synoptic periods. During each of the two regimes, the net transports by the transient disturba...
240 citations
TL;DR: A multi-level, global, spectral transform model of the atmosphere based upon spherical harmonies has been developed at GFDL as mentioned in this paper, which has been widely used for extended range weather prediction experiments.
Abstract: A multi-level, global, spectral transform model of the atmosphere, based upon spherical harmonies, has been developed at GFDL. The basic model has nine sigma levels in the vertical and rhomboidal spectral truncation at wavenumber 30. However, finer spectral or vertical resolution versions are available as well. The model's efficient semi-implicit time differencing scheme does not appear to adversely affect medium range predictions. The model has physical processes commonly associated with grid point GCM'S. Two unique features are a linearized virtual temperature correction and an optional, spectrally-computed non-linear horizontal diffusion scheme. A parameterization of vertical mixing based upon the turbulent closure method is also optional. The GFDL spectral model has been widely utilized at GFDL for extended range weather prediction experiments. In addition, it has been adapted and applied to climate studies, four-dimensional data assimilation experiments and even to the atmosphere of Venus. T...
TL;DR: In this article, the mesoscale updraft in the anvil cloud of a tropical squall system was inferred, and quantitative profiles of the mes-oscale anvil updraft and downdraft were obtained.
Abstract: Composites of radar and wind observations in a coordinate system attached to a moving tropical squall line confirm that such a squall system is composed of two separate circulation features: a convective squall-line region and a stratiform anvil region. The squall-line region is characterized by mesoscale boundary-layer convergence, which feeds deep convective updrafts, and mid-to-upper-level divergence associated with outflow from the cells. The anvil region is characterized by mid-level convergence, which feeds both a mesoscale downdraft below the anvil and a mesoscale updraft within the anvil cloud. Before this study, the mesoscale updraft in the anvil cloud of the tropical squall system had been somewhat speculative, and both the anvil updraft and downdraft had been inferred only qualitatively. The occurrence of the anvil updraft is now proven and quantitative profiles of the mesoscale anvil updraft and downdraft have been obtained.
TL;DR: In this paper, a long-term series of average Northern Hemisphere temperatures based on monthly mean station data gridded on a 5° latitude by 10° longitude grid is presented.
Abstract: We have produced, using objective techniques, a long-term series of average Northern Hemisphere temperatures based on monthly mean station data gridded on a 5° latitude by 10° longitude grid. Difficulties in the estimation of this parameter are discussed, deficiencies in the currently available data base and possible effects on the estimated average are described, and monthly mean data are presented. Long-term trends and extremes are identified in the annual and seasonal data. All seasons show similar long-term trends, but there are noticeable differences on time scales of 10 years and less. For example, for winter temperature, the early 20th century warming peaked during the 1940's whereas the maximum in the other seasons was in the previous decade. Both the magnitude of the long-term trends and the year-to-year variability has been greatest in winter. There is evidence that the long-term cooling that characterized the 1940's, 1950's and 1960's has ended. Warming began in the mid to late 1960's ...
TL;DR: In this paper, the interannual variability in the upper tropospheric tropical wind field is described through empirical orthogonal functions, teleconnections and composite analyses using 11 years of mean monthly analyzed fields of zonal and meridional components of the 200 mb wind on a 5° Mercator grid.
Abstract: The interannual variability in the upper tropospheric tropical wind field is described through empirical orthogonal functions, teleconnections and composite analyses. The data used are 11 years of mean monthly analyzed fields of zonal and meridional components of the 200 mb wind on a 5° Mercator grid extending from 48.1° N to 48.1°S derived from the National Meteorological Center's operational tropical analysis. A substantial portion of the interannual variability in the 200 mb circulation is shown to be related to the Southern Oscillation. The anomalous circulation in the Pacific is characterized by a pair of anticyclonic/cyclonic anomalies straddling the equator during periods of low/high Southern Oscillation Index. Zonal wind differences of 8–11 m s−1 between low- and high-Index phases of the SO were found near 25°N, 25°S and near the equator in the central Pacific. Composites relative to El Nino events during different seasons reveal that anomalous anticyclonic circulations in the Pacific are...
TL;DR: In this article, aircraft, ship, buoy, and land nation data were composited with respect to the center of Hurricane Frederic for two time periods: a 24 h period corresponding to the storm's position in the open Gulf of Mexico on 12 September 1979, and an 8 h period correspond to the landfall of Frederic near 0400 GMT on 13 September.
Abstract: Numerous aircraft, ship, buoy and land nation data were composited with respect to the center of Hurricane Frederic for two time periods: a 24 h period corresponding to the storm’s position in the open Gulf of Mexico on 12 September 1979, and an 8 h period corresponding to the landfall of Frederic near 0400 GMT on 13 September. Comparison of wind analyses for the two periods indicated a rotation of maximum inflow angles from the southeast to northeast quadrants and a strong frictional decrease of wind speed over land. Them and other features of the landfall analysis were compared with a model landfall study by Moss and Jones (1978). The landfall composite wind field was compared with the Fujita damage vector analysis to determine the damage time interval and mean wind speed range. Damage vector directions were found to be well correlated with the surface streamlines, with the most severe damage being associated with Frederic’s northern eyewall. Ten-meter-level wind speed data over water (VO) and ...
TL;DR: In this article, a monthly storm-track climatology is derived from monthly maps of cyclone tracks for the winter season, October through March, averaged over 23 years, 1957/58-1979/80, for a 2° latitude×4° longitude grid bounded by 51°N, 65°N and 157°W and 171°E.
Abstract: A monthly storm-track climatology is derived from monthly maps of cyclone tracks for the winter season, October through March, averaged over 23 years, 1957/58–1979/80, for a 2° latitude×4° longitude grid bounded by 51°N, 65°N, 157°W and 171°E. There is a decrease in the number of cyclones with latitude in all months and division into two storm tracks, one propagating north-northeast along the Siberian peninsula and one entering the southern Bering Sea on a northeasterly course and either curving northward into the central Bering Sea or continuing parallel to the Aleutian Island chain. Monthly average ice extents are established for February and March 1958–80 along a line from Norton Sound southwest toward the ice edge, perpendicular to the average maximum extent. Comparison of composite cyclone charts summed over the winter season and over the five heaviest and five lightest ice years shows a shift in cyclone centers toward the west in light ice years. The correlation between maximum seasonal ice...
TL;DR: The locations and frequencies of cross-equatorial tropical cyclone pairs over the Pacific Ocean are compared between years of contrasting equatorial Pacific sea surface temperature (SST) and atmospheric circulation anomalies, i.e., high versus low Southern Oscillation (SO) indices, during the period 1971-79 as discussed by the authors.
Abstract: The locations and frequencies of cross-equatorial tropical cyclone pairs over the Pacific Ocean are compared between years of contrasting equatorial Pacific sea surface temperature (SST) and atmospheric circulation anomalies, i.e., high versus low Southern Oscillation (SO) indices, during the period 1971–79. Weak southeast trade winds associated with low SO indices allow warm (29°C) surface water in the equatorial (0–5°S) zone to extend eastward across the dateline, encouraging formation of cyclone pairs near the dateline. The cyclone pairs, in turn, provide the linkage between warm water and equatorial convection (as indicated by Canton Island rainfall) during southern summer. In general, the occurrences of cyclone pairs vary in longitude with the eastward excursions of warm equatorial water, furthermore, cyclone pairs appear to provide a positive feedback by advancing the eastward warm water extent. In 1974–75, when no cyclone pairs developed near the dateline in spite of sufficiently high SST'...
TL;DR: In this paper, the short-term teleconnections between planetary-scale circulation components over the monsoon region were studied. But the results basically verify the shortterm teleconnection model proposed by Chang and Lau (1980), but more complex processes in the acceleration of the midlatitude jet streaks are indicated.
Abstract: Objectively analyzed 200 mb winds of four winters are used to study the short-term (several days) teleconnections between planetary-scale circulation components over the monsoon region. The composited structures suggest that during very actively northeasterly monsoon (surge) periods, the midlatitude and tropical circulation components vary in a coherent way. The jet streak and local Hadley circulation over East Asia, the divergent flow over the maritime continent, and the equatorial Walker circulations over the Pacific and Indian Oceans all strengthen steadily, while the secondary jet streak over West Asia weakens. During inactive (break) periods the midlatitude circulation components all exhibit reversed changes, while the variations in the tropics are less coherent, although still showing reversed tendencies. The results basically verify the short-term teleconnection model proposed by Chang and Lau (1980), but more complex processes in the acceleration of the midlatitude jet streaks are indicated. In addition, the contrast between the very active and break monsoon periods suggests the relative importance of tropical versus midlatitudinal forcings in different regions of the monsoon circulation.
TL;DR: In this article, the authors analyzed monthly sea-level pressure anomalies at Easter Island, Rapa, Tahiti and Darwin, for the period 1951-79, to reveal their temporal characteristics and the coherence and time lead/lag relationships among them.
Abstract: Monthly sea-level pressure anomalies at Easter Island, Rapa, Tahiti and Darwin, for the period 1951–79, are analysed to reveal their temporal characteristics and the coherence and time lead/lag relationships among them. For interannual scale oscillations, the pressure variations at Rapa and Easter Island lead those at Tahiti and those of opposite phase at Darwin by 2–8 months, where the large lead times are associated with lower frequency oscillations. Of the four stations, Rapa has the smallest percentage of its variance in the range of periods containing the Southern Oscillation; Darwin has the largest. Spatial smoothing by combining stations enhances the percentage of variance in the longer periods. Combining Tahiti and Darwin gives a substantial increase; combining Rapa and Easter Island, much less. Normalization of the time series through division by the monthly standard deviations is also treated. The combination of Tahiti and Darwin is recommended as a Southern Oscillation Index for diagno...
TL;DR: In this article, the second-order approximation of the first spatial partial derivative is replaced with one that includes information about the dimensionality of the field, and also considering the cross-space difference.
Abstract: The conservation form of the second-order Crowley advection scheme, as some authors have pointed out, may lead to numerical instability for multi-dimensional blows. Replacing the original second-order-accurate approximation of the first spatial partial derivative, with one that includes information about the dimensionality of the field, and also considering the cross-space difference, eliminates this instability without destroying the level of conservation or the accuracy of the original Crowley scheme. The paper also presents some flux correction solutions, the use of which avoids the development of negative values in the solution for positive definite scalars. The paper also discusses the solution of the advection equation in the em of strong deformational flow.
TL;DR: In this paper, the authors describe annual and seasonal changes in air temperatures over high latitudes of the Northern Hemisphere during the period 1881-1980, and identify the spatial patterns of change associated with the trend in Arctic temperatures.
Abstract: We describe annual and seasonal changes in air temperatures over high latitudes of the Northern Hemisphere during the period 1881–1980. Trends (that is, fluctuations on time scales greater than 20 years) in the average temperature of the Arctic are compared with those of the Northern Hemisphere. Seasonal and regional departures from the long-term trends in the average temperature of the Arctic are identified. Spatial patterns of variation in the Arctic temperature field are determined by principal component analysis and the major characteristics of the time series of the dominant patterns are summarized. Trends in Arctic temperatures have been broadly similar to those for the Northern Hemisphere during the study period. The Arctic variations were, however, greater in magnitude and more rapid. The spatial pattern of change associated with the trend in Arctic temperatures is clearly identified by principal component analysis. It shows that the trends have, in general, been Arctic-wide, but that cer...
TL;DR: In this article, the authors described the annual cycle in sea surface temperature (SST), surface wind and other atmospheric variables in the tropical Pacific, where the primary data sets of SST and surface wind were derived from ship observations in the Pacific between 29°N and 29°S during the period 1946-76.
Abstract: The annual cycle in sea surface temperature (SST), surface wind and other atmospheric variables in the tropical Pacific are described. The primary data sets of SST and surface wind are derived from ship observations in the Pacific between 29°N and 29°S during the period 1946–76. The annual cycle in SST away from the equator can be attributed to the annual cycle in solar heating. However, in the eastern equatorial Pacific, the annual cycle in SST undergoes systematic longitudinal changes in phase and amplitude. Near the coast of Peru, the warmest temperatures occur during March, while further west along the equator, the warmest temperatures occur progressively later and with diminished amplitude. The annual cycle in surface wind convergence along the equator displays similar changes with longitude. The annual cycle in surface wind is dominated by the meridional migrations of the trade wind belts. Near the equator, the amplitude of the annual cycle in meridional wind is larger than that in zonal wi...
TL;DR: In this article, an algorithm for location of hurricane centers by least squares using aircraft data has been developed, where a cubic spline storm track is first constructed using centers based on winds in a coordinate system fixed to the earth.
Abstract: An algorithm for location of hurricane centers by least squares using aircraft data has been developed. As the aircraft traverses the eye, lines of position normal to the wind are constructed each 100 m along its track. An additional line of position is constructed normal to the track at the closest point of approach to the center. The center coordinates are then chosen such that the sum of the squares of the normal distances from the center to the lines of position is minimized. A cubic spline storm track is first constructed using centers based on winds in a coordinate system fixed to the earth. A track based upon winds in moving, storm-centered coordinates may be obtained by transformation of the winds into such a coordinate system and iterative redetermination of the centers. For intense hurricanes, the centers can be located with an accuracy of 3 km and the mean motion over a period of four to six hours determined to within 4° of direction and 0.5 m s−1 of speed. The details of the track osc...
TL;DR: In this paper, a new general circulation model, developed to run on a coarse grid (8 x 10 deg resolution) at the Goddard institute for Space Studies, was employed to investigate the potential use of ground moisture anomalies for seasonal climate prediction.
Abstract: A new general circulation model, developed to run on a coarse grid (8 x 10 deg resolution) at the Goddard institute for Space Studies is employed to investigate the potential use of ground moisture anomalies for seasonal climate prediction. For three different summertime simulations, the ground moisture on 1 June over the United States is reduced to 1/4 of its value in the control run. The results show that the subsequent surface air temperature is significantly higher throughout most of the summer, while the precipitation decreases, especially in June and July. Knowledge of late spring ground moisture anomalies should thus be an aid in predicting summertime climate.
TL;DR: In this article, the authors investigated the mid-troposphere circulation associated with the Southern Oscillation (SO) using mean monthly 700 mb height data for the period 1951-79.
Abstract: Variations in the mid-troposphere circulation associated with the Southern Oscillation (SO) are investigated and documented using mean monthly 700 mb height data for the period 1951–79. The SO was defined by a Southern Oscillation Index (SOI) consisting of the difference in normalized mean monthly sea-level pressures at Tahiti and Darwin. Results for all four seasons are presented in the form of lagged, as well as contemporaneous, correlations and composites of height anomalies obtained separately for high and low SOI values. Different SO teleconnection patterns are observed for each season. Strongest SO signals appear in the winter with SOI leading the height field by one to two seasons. The time lead may he useful in prognostic applications. The correlation in the summer is negligible. The winter teleconnection pattern over the North Pacific-North America-North Atlantic sector is similar to that shown by Bjerknes and others. Patterns for other seasons are also presented. The statistical signifi...
TL;DR: Application of some simple semi-Lagrangian advective schemes, based on a multiply-upstream interpolation, to a multi-level split explicit model shows that they enable full advantage to be taken of the splitting method by allowing a long time step for advection.
Abstract: The stability properties of some simple semi-Lagrangian advective schemes, based on a multiply-upstream interpolation, are examined. In these schemes, the interpolation points are chosen to surround the departure points of the fluid particles at the beginning of a time step. It is shown that the schemes, though explicit, are unconditionally stable for a constant wind field. Application of the schemes to a multi-level split explicit model shows that they enable full advantage to be taken of the splitting method by allowing a long time step for advection. It is shown that they can thus lead to a considerable saving of computer time compared to Eulerian schemes, while giving comparable accuracy.
TL;DR: In this paper, the authors attributed the development and maintenance of the drought-producing cell to several physical factors such as subsidence, dry soil, lack of cloud and high insolation.
Abstract: The protracted heat wave and drought of the Great Plains during summer 1980 was a manifestation of an abnormal form of the general circulation. An upper-level continental high developed rapidly over the Southern Plains in late May and persisted with only small changes throughout the summer. The associated subsidence, dry soil, lack of cloud and high insolation led to unrelenting heat. Descriptions of several interlocking features are given followed by an attempt to ascribe the development and maintenance of the drought-producing cell to several physical factors. Strong low-latitude westerlies (expanded circumpolar vortex) over the North Pacific, North America and North Atlantic during spring 1980 led to latitudinally depressed storm tracks relative to normal. Combined with normal seasonal forcing this anomalous pattern was stable in spring but unstable in summer after the climatologically dependable northward march of the westerlies. Moreover, normal spring to summer mid-tropospheric height chang...
TL;DR: In this article, numerical simulations with a primitive equation model which includes parameterized physics are conducted to study the effects of an island mountain range on translating tropical cyclones, and the initial state contains a nonlinearly balanced vortex embedded in a uniform, unsheared, tropical easterly flow.
Abstract: Numerical simulations with a primitive equation model which includes parameterized physics are conducted to study the effects of an island mountain range on translating tropical cyclones. The idealized topography with a 200 m peak is introduced over a 12 h growth period. The initial state contains a nonlinearly balanced vortex embedded in a uniform, unsheared, tropical easterly flow. Many orographic effects are produced similar to those observed for typhoons passing over mountain ranges. The storm tends to translate at about twice the speed of the basic flow near the mountain, while its intensity is reduced. Air flows mostly around the mountain range instead of over it, forming a ridge on the windside and a trough on the leeside slopes. The tropical cyclone's passage induces a mean cyclonic circulation around the mountain with strongest amplitudes at low levels. As a result, the model tropical cyclone makes a cyclonic curvature in its path around the north end of the island mountain. Further nume...
TL;DR: In this paper, the authors evaluated the long-term fluctuations of snow cover in the United States in the context of short-term climatic variability using 2.5 and 15.0 cm snow coverage digitized weekly for the winters of 1949-50 through 1980-81.
Abstract: Interannual fluctuations of snow cover in the United States are evaluated in the context of short-term climatic variability. The analysis is based on 2.5 and 15.0 cm snow coverage digitized weekly for the winters of 1949–50 through 1980–81. The winter of least snow (1980–81) and the winters of most snow (1977–78 and 1978–79) have occurred in the most recent portion of the record. Considerable persistence of departures from normal snow cover is evident in the monthly lagged autocorrelations, which range from 0.35 in the lee of the Rockies to 0.75 in the Far, West. Fluctuations of surface temperature are most highly correlated with snow cover in a broad east-west band which straddles the normal wintertime position of the snow edge. Snow anomalies in the eastern and western United States are associated with opposite phases of a three-cell field of 760 mb height anomalies over the North Pacific Ocean and North America. A series of regression analyses shows that a portion of the surface temperature va...
TL;DR: In this article, an index of the date of onset of the North Australian wet season is defined based on rainfall received at a single station (Darwin), and it is demonstrated that this index can be predicted some months ahead.
Abstract: An index of the date of onset of the North Australian wet season is defined based on rainfall received at a single station (Darwin). It is demonstrated that this index can be predicted some months ahead. The amount of rain received during the wet season is only weakly related to the date of onset, and the amount of rainfall received in the middle and late portion of the season is totally unrelated to either the date of onset or to the amount of rain received in the early part of the season. Discussion is presented on the relationship between the wet-season onset as here defined and the Australian monsoon onset as defined by Troup (1961). A distinction is made between the monsoon portion of the season and an earlier transition season which also accounts for a large proportion of the total rainfall.