Showing papers in "Monthly Weather Review in 1987"
TL;DR: In this article, the amplitude and phase of the Arm harmonic fitted to the 24-month composite values are plotted in the form of a vector for each station, which reveals both the regions of spatially coherent ENSO-related precipitation and the phase of this signal in relation to the evolution of the composite episode.
Abstract: We investigate the “typical” global and large-scale regional precipitation patterns that are associated with the El Nino/Southern Oscillation (ENSO). Monthly precipitation time series from over 1700 stations are analyzed using an empirical method designed to identify regions of the globe that have precipitation variations associated with ENSO. Monthly mean ranked precipitation composites are computed over idealized 2-year ENSO episodes for all stations that include data for at least five ENSOs. The amplitude and phase of the Arm harmonic fitted to the 24-month composite values are plotted in the form of a vector for each station. When plotted on a global map, these vectors reveal both the regions of spatially coherent ENSO-related precipitation and the phase of this signal in relation to the evolution of the composite episode. Time cries of precipitation for the coherent regions identified in the harmonic vector map are examined to determine the magnitudes of the ENSO-related precipitation and th...
3,608 citations
TL;DR: In this article, Orthogonally rotated principle component analysis (RPCA) was used to identify and describe the seasonality and persistence of the major modes of interannual variability.
Abstract: 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...
3,330 citations
TL;DR: In this article, a coupled atmosphere-ocean model is developed and used to study the ENSO (El Niñ/Southern Oscillation) phenomenon, which reproduces certain key features of the observed phenomenon including the recurrence of warm events at irregular intervals with a preference for three to four years.
Abstract: A coupled atmosphere-ocean model is developed and used to study the ENSO (El Niñ/Southern Oscillation) phenomenon. With no anomalous external forcing, the coupled model reproduces certain key features of the observed phenomenon. including the recurrence of warm events at irregular intervals with a preference for three to four years. It is shown that the mean sea surface temperature, wind and ocean current fields determine the characteristic spatial structure of ENSO anomalies. The tendency for phase-locking of anomalies is explained in terms of a variation in coupling strength associated with the annual cycle in the mean fields. Sensitivity studies reveal that both the amplitude and the time of scale of the oscillation are sensitive to several parameters that affect the strength of the atmosphere–ocean coupling. Stronger coupling implies larger oscillations with a longer time scale. A critical element of the model oscilliation is the variability in the equatorial heat content of the upper o...
1,530 citations
823 citations
TL;DR: In this article, the authors presented estimates of areal and time-averaged convective precipitation derived from geostationary satellite imagery using a simple thresholding technique, which is based on measurements of the monthly mean fraction of 2.5° × 2. 5° areas covered by clouds whose equivalent blackbody temperature in infrared imagery is below 235 K.
Abstract: Estimates of areal- and time-averaged convective precipitation derived from geostationary satellite imagery using a simple thresholding technique are presented. The estimates are based on measurements of the monthly mean fraction of 2.5° × 2.5° areas covered by clouds whose equivalent blackbody temperature in infrared imagery is below 235 K. The transformation between fractional coverage and rainfall amount is based upon comparisons of fractional coverages using a variety of temperature thresholds and spatial and temporal averaging scales with areal averaged rainfall from the GARP Atlantic Tropical Experiment. Three-year means of the estimated precipitation for the period December 1981-November 1984 are shown for each of the (3-month) calendar seasons and compared with published descriptions of the long-term seasonal mean rainfall fields. Over the tropical oceans agreement is quite good with no evidence of any systematic errors. Over the Americas, long-term means derived from station observations...
744 citations
TL;DR: In this article, a vertically integrated measure of the moist static stability, the gross moist stability, is proposed, and the positions of these minima are determined by the time-mean moisture field, which is, in turn, closely tied to the time mean surface temperature.
Abstract: The vertically integrated moist static energy equation provides a convenient starting point for the construction of simple models of the time-mean low level convergence in the tropics. A vertically integrated measure of the moist static stability, the “gross moist stability,” proves to be of central importance. Minima in this quantity mark the positions of the tropical convergence zones. We argue that the positions of these minima are determined by the time-mean moisture field, which is, in turn, closely tied to the time-mean surface temperature.
728 citations
TL;DR: In this paper, a general framework for forecast verification based on the joint distribution of forecasts and observations is described, and two factorizations of the joint distributions are investigated: 1) the calibration-refinement factorization, which involves the conditional distributions of observations given forecasts and the marginal distributions of forecasts, and 2) the likelihood-base factorization.
Abstract: A general framework for forecast verification based on the joint distribution of forecasts and observations is described. For further elaboration of the framework, two factorizations of the joint distribution are investigated: 1) the calibration-refinement factorization, which involves the conditional distributions of observations given forecasts and the marginal distribution of forecasts, and 2) the likelihood-base factorization, which involve the conditional distributions of forecasts given observations and the marginal distribution of observations. The names given to the factorizations reflect the fact that they relate to different attributes of the forecasts and/or observations. Several examples are used to illustrate the interpretation of these factorizations in the context of verification and to describe the relationship between the respective factorizations. Some insight into the potential utility of the framework is provided by demonstrating that basic elements and summary measures of the...
668 citations
TL;DR: The authors found that virtually all forecast skill was due to three climatological features: a decadal scale change in Northern Hemisphere temperature, ENSO-related phenomena, and the occurrence of two distinct short-lived, but large-scale coherent structures in the atmospheric field of the Northern Hemisphere.
Abstract: Statistical techniques have been used to study the ability of SLP, SST and a form of persistence to forecast cold/warm season air temperatures over the United States and to determine the space–time evolution of these fields that give rise to forecast skill. It was found that virtually all forecast skill was due to three climatological features: a decadal scale change in Northern Hemisphere temperature, ENSO-related phenomena, and the occurrence of two distinct short-lived, but large-scale, coherent structures in the atmospheric field of the Northern Hemisphere. The physical mechanisms responsible for the first two signals are currently unknown. One of the large-scale, coherent features seems largely independent of the ENSO phenomena, while the second is at least partially related to ENSO and may be part of a recently discovered global mode of SLP variation. Both features resemble various combinations of known teleconnection patterns. These large-scale coherent structures are essentially stationar...
641 citations
TL;DR: In this article, the authors studied the annual cycle of outgoing longwave radiation (OLR), clouds, precipitation and sea level pressure from satellite and station data in the tropical Indian and Pacific sectors.
Abstract: The annual cycle of outgoing longwave radiation (OLR), clouds, precipitation and sea level pressure is studied from satellite and station data in the tropical Indian and Pacific sectors. A region of heavy convection, termed the tropical convective maximum, moves from north to south and west to cast in the Indian and Pacific sectors as the mean annual cycle proceeds from northern summer to northern winter. During its return excursion northwestward from northern winter to northern summer in the Indian sector, it is not as strong as in the preceding half of the annual cycle. To study interannual fluctuations of the annual cycle in these regions, Indian monsoon rainfall is chosen as an indicator of precipitation and convection in the summer monsoon region. Relatively strong and weak years of monsoon rainfall are selected and used as a starting point to follow the evolution of the annual cycle in the two sets of years. More than two-thirds of the monsoon seasons since 1900 are classified as either rel...
554 citations
TL;DR: In this article, the authors examined the life cycles of the 30-60 day atmospheric oscillation by compositing 30-day filtered NMC global wind analyses (250 mb and 850 mb) and outgoing longwave radiation (OLR) for the years 1979-84.
Abstract: Life cycles of the 30–60 day atmospheric oscillation were examined by compositing 30–60 day filtered NMC global wind analyses (250 mb and 850 mb) and outgoing longwave radiation (OLR) for the years 1979–84. Separate composite life cycles were constructed for the May–October and November–April seasons using empirical orthogonal function analysis of the large-scale divergent wind field (250 mb velocity potential) to define the oscillation's phase. Monte Carlo simulations were used to assess the statistical significance of the composite OLR and vector wind fields. Large-scale (wavenumber one) tropical divergent wind features propagate eastward around the globe throughout the seasonal cycle. The spatial relationships between these propagating circulation features and OLR are shown using sequences of composite maps. Good agreement exists between areas of upper-air divergence and areas of convection inferred from the OLR satellite data. Convection anomalies are smaller over tropical Africa and South Am...
523 citations
TL;DR: In this paper, a number of physical factors that influence the relation between measured radar reflectivity and surface rainfall are considered both theoretically and through detailed comparisons of radar and raingauge measurements.
Abstract: A number of physical factors that influence the relation between measured radar reflectivity and surface rainfall are considered both theoretically and through detailed comparisons of radar and raingauge measurements. These factors include natural differences in raindrop-size distributions, enhancement of radar reflectivity by presence of hailstones or melting snow, diminution of reflectivity by downdrafts, and low-level changes in rainfall rate caused by accretion or evaporation. Results of 374 comparisons in twenty storms, which cover a wide variety of synoptic situations and rainfall patterns, are presented. Magnitudes of the effects of the different factors are estimated, and storm types where they are likely to be significant are pointed out. Also, some ways of compensating for the observed effects are suggested.
TL;DR: In this article, the authors examined the evolution of the Southern Oscillation (SO) in the time domain by computing lagged cross correlations between sea level pressures at Darwin and sea level or surface pressures at selected stations.
Abstract: The evolution of the Southern Oscillation (SO) is examined in the time domain by computing lagged cross correlations between sea level pressures at Darwin and sea level or surface pressures at selected stations. Also, in the Northern Hemisphere, the historical and U.S. Navy sea level pressure analyses are used. All monthly time series are low-pass filtered to retain periodicities greater than 20 months in order to highlight the interannual fluctuations which are primarily associated with the SO. A detailed analysis of the post-1941 period results in plotted maps of the phase (lead or lag) and magnitude of the maximum cross correlations with Darwin, in a manner analogous to a broadband coherence and phase spectrum. The relationships within the SO are further examined, where possible, back to 1882 using time series of running decadal cross covariances. The dominant pattern reveals the two poles of the traditional standing oscillation or seesaw of the SO, with centers of opposite sign over Indonesia...
TL;DR: In this paper, the authors studied the time evolution of the general circulation over Asia during an 80-day period from mid-April to early July 1979 using objectively analyzed FGGE Level II-b data.
Abstract: The time evolution of the general circulation over Asia during an 80-day period from mid-April to early July 1979 is studied using objectively analyzed FGGE Level II-b data. Through the analyses of the wind, temperature, precipitation, outgoing longwave radiation (OLR) flux, and heat and moisture budgets in the area 0°–50°N, 40°–130°E, the major changes of the circulation leading to the onset of the summer monsoon and the role of the Tibetan Plateau in these changes are examined. During the analyzed period the general circulation underwent two distinct stages of abrupt transitions resulting in the successive onsets of early summer rains over Southeast Asia and the Indian summer monsoon. The first transition occurred in May in which low-level southwesterlies began over the longitudes east of 80°E (from the Bay of Bengal to the South China Sea), resulting in the spreading of early summer rains over Assam, the Bay of Bengal coasts of Burma and the Malay Peninsula, Thailand, Indochina and the South C...
TL;DR: In this article, the authors examined 13 cases of mesoscale wave disturbances and their environment to isolate common features for these cases and to determine possible energy sources for the waves, which is consistent with the hypothesis that the energy source needed to initiate and sustain the wave disturbances may be related to a geostrophic adjustment process associated with upper-tropospheric jet streaks.
Abstract: Published data on 13 cases of mesoscale wave disturbances and their environment were examined to isolate common features for these cases and to determine possible energy sources for the waves. These events are characterized by either a singular wave of depression or wave packets with periods of 1-4 h, horizontal wavelengths of 50-500 km, and surface-pressure perturbation amplitudes of 0.2-7.0 mb. These wave events are shown to be associated with a distinct synoptic pattern (including the existence of a strong inversion in the lower troposphere and the propagation of a jet streak toward a ridge axis in the upper troposphere) while displaying little correlation with the presence of convective storm cells. The observed development of the waves is consistent with the hypothesis that the energy source needed to initiate and sustain the wave disturbances may be related to a geostrophic adjustment process associated with upper-tropospheric jet streaks.
TL;DR: In this paper, the authors investigated the heat budget of the Siberian high by using a compositing method and selected several cases of strong Siberian high that moved over China from the northwest from datasets covering five winters (December through February of 1980-1984).
Abstract: The heat budget of the Siberian high is investigated by using a compositing method. Ninteen cases of strong Siberian highs that moved over China from the northwest were selected from datasets covering five winters (December through February of 1980–1984). The apparent heat source (Q1)and the apparent moisture sink (Q2) were estimated via budget calculations. The diabatic heating terms were also calculated via direct use of physical parameterization schemes. The vertical transports of sensible and latent heat from subgrid-scale of motions were estimated as residuals from the thermodynamic energy equation. Over the region of the region of the Siberian high, strong radiative cooling and large-scale descending motion (with large-scale mass convergence over the upper and middle tropospheric and divergence over the lower troposphere) contributes to a rapid buildup of the Siberian high. Heating in the upper troposphere due to subgrid-scale sensible heat transfer is also an important factor in the mainte...
TL;DR: In this paper, the authors examined synoptic and statistical relationships between the summer monsoon rainfall over India, the Southern Oscillation, and the mid-tropospheric circulation over India.
Abstract: Forty-six years (1939-1984) of observed data were examined to study synoptic and statistical relationships between the summer monsoon rainfall over India, the Southern Oscillation, and the midtropospheric circulation over India. The change in Darwin pressure from January to April and the latitudinal position of the April 500-mb ridge along 75 deg E are taken as two quasi-independent predictor parameters to develop a regression equation to predict the summer monsoon rainfall. Verification of predictions on independent data shows that the root-mean-square error for predicted rainfall is 36 mm, which is less than half of the standard deviation and only about 4 percent of the mean rainfall (857 mm).
TL;DR: In this article, the relative airflow and accompanying precipitation structure of squall lines trailed by mesoscale regions of stratiform rain are examined with emphasis on the occurrence of "rear inflow", i.e., the intrusion of environmental air into these storms across the trailing precipitation boundary.
Abstract: The relative airflow and accompanying precipitation structure of squall lines trailed by mesoscale regions of stratiform rain are examined with emphasis on the occurrence of “rear inflow,” i.e. the intrusion of environmental air into these storms across the trailing precipitation boundary. Three cases from Kansas and Oklahoma provide examples of “Strong Rear Inflow,” which crosses the back edge of the stratiform precipitation area at relative speeds exceeding 10 m s−1. The vertical profiles of relative flow at the trailing precipitation boundary of these three systems were remarkably similar, with the rear inflow confined to a jet-like layer centered at about 550 mb. Doppler radar data for two of these cases showed that the rear inflow jet occupied a continuous channel extending from middle levels at the back edge of the stratiform region to lower levels of the leading convective region, where it merged with outflow from convective downdrafts to bolster the leading gust front. Strong front-to-rea...
TL;DR: In this paper, an objective algorithm is devised which is capable of touting tropical cloud clusters at the point of initiation, tracking them to the paint of dissipation and thereby accumulating statistics on their size distributions and preferred geographical locations and times of occurrence.
Abstract: An objective algorithm is devised which is capable of touting tropical cloud clusters at the point of initiation, tracking them to the paint of dissipation and thereby accumulating statistics on their size distributions and preferred geographical locations and times of occurrence. The technique is able to account for periods of growth, mergers, splits and decay, which take place during the lifetime of an individual cluster. It is used to derive statistics on cloud clusters observed during the Winter Monsoon Experiment, which was conducted in the region of the “maritime continent,” near Borneo, in December, 1978. The size distribution of the clusters identified and tracked shows that by far most of the cumulative cloud cover was accounted for by a few very large clusters. This result implies that the vertical distribution of diabatic heating in the region of the experiment was strongly influenced by dynamical and radiative processes in the widespread stratiform cloud and precipitation areas that t...
TL;DR: The mean anomalies of the Quasi-Biennial Oscillation for the winter as a whole (west minus east phase) computed from years with no Cold or Warm Events are zonally symmetrical and shaped as four concentric regions with alternatin... as mentioned in this paper.
Abstract: The mean anomalies of 50 mb height in the northern winter for seven Warm Events in the Southern Oscillation show a weak polar vortex and an enhanced Aleutian high. In the mean for six Cold Events the polar vortex is unusually strong and the Aleutian high is weakened and displaced far to the southwest. These anomalies are consistent with the corresponding anomalies in sea level pressure pattern. The Warm Events of 1963 and 1982 did not fit this pattern as in both years the polar vortex was cold and intense. These events happened in years when volcanoes injected large amounts of gases and aerosols into the stratosphere and the temperature of the tropical stratosphere became unusually high. In other Warm Events the temperature of the tropical stratosphere was abnormally low. The mean anomalies of the Quasi-Biennial Oscillation for the winter as a whole (west minus east phase) computed from years with no Cold or Warm Events are zonally symmetrical and shaped as four concentric regions with alternatin...
TL;DR: In this paper, the authors compared four different conjugate-gradient methods, representative of up-to-date available scientific software, by applying them to two different meteorological problems of interest using criteria of computational economy and accuracy.
Abstract: During the last few years new meteorological variational analysis methods have evolved, requiring large-scale minimization of a nonlinear objective function described in terms of discrete variables. The conjugate-gradient method was found to represent a good compromise in convergence rates and computer memory requirements between simpler and more complex methods of nonlinear optimization. In this study different available conjugate-gradient algorithms are presented with the aim of assessing their use in large-scale typical minimization problems in meteorology. Computational efficiency and accuracy are our principal criteria. Four different conjugate-gradient methods, representative of up-to-date available scientific software, were compared by applying them to two different meteorological problems of interest using criteria of computational economy and accuracy. Conclusions are presented as to the adequacy of the different conjugate algorithms for large-scale minimization problems in different met...
TL;DR: A generalized forward-in-time upstream advective operator following the methodology of Crowley is developed and a new flux form is derived which does reduce to the Advective form under the conditions of constant velocity and grid spacing.
Abstract: A generalized forward-in-time upstream advective operator following the methodology of Crowley is developed and advective schemes of orders 1 through 10 are tested analytically and numerically. Flux forms of these schemes are also derived with Crowley’s methodology. It is shown that thew flux forms do not reduce to the advective form with constant velocity and grid spacing for schemes of order 3 and higher and they are not as accurate as the advective form. A new flux form is derived which does reduce to the advective form under the conditions of constant velocity and grid spacing. The schemes were tested in two dimensions using time splitting. In the rotating cone test, the advective and new flux forms performed identically, while the other flux form had larger dissipation and dispersion errors. In the deformational flow field test, the advective forms were unstable for both time steps tested. Use flux forms were less unstable for the higher Courant number and the domain as a whole was stable fo...
TL;DR: In this paper, the analysis of a tropical squall line, observed on 22 June 1981 during the COPT 81 (Convection Profonde Tropicale) experiment, is presented.
Abstract: This paper deals with the analysis of a tropical squall line, observed on 22 June 1981 during the COPT 81 (Convection Profonde Tropicale) experiment. The present Part I is restricted to the study of the kinematic structure of the system, which moved in a moderately unstable atmosphere, faster than the environmental air at all levels. At the observation time, the squall line was in a mature stage. The explicit description of the airflow within the system was inferred from dual- and single-Doppler radar data. The general characteristics of the squall line are found to be very similar to those of tropical squall lines observed during previous experiments such as VHIMEX or GATE: a large cloud system composed of an organized convective line ahead of an extensive trailing anvil cloud (stratiform rain), fast motion and long-lasting structure and a well-marked gust front signature at ground level. The overall airflow presents a three-dimensional structure. At the leading edge, convective-scale updrafts a...
TL;DR: In this paper, the authors presented the NESDIS operational technique for estimating convective rainfall from GOES data, which consists of two steps: locating the active portion of the convective system and computing half-hourly rainfall estimates based on cloud-top temperature and cloud growth or divergence aloft, overshooting tops, mergers, saturated environment (stationary storms), and a moisture correction factor.
Abstract: This paper presents the NESDIS operational technique for estimating convective rainfall from GOES data. Estimates and 3-hour outlooks are computed on the Interactive Flash Flood Analyzer (IFFA) and transmitted via the Automation of Field Operations and Services (AFOS) computer systems to Weather Service Forecast Offices, Weather Service Offices, and River Forecast Centers. The technique consists of two steps: (1) locating the active portion of the convective system and (2) computing half-hourly rainfall estimates based on cloud-top temperature and cloud growth or divergence aloft, overshooting tops, mergers, saturated environment (stationary storms), and a moisture correction factor. A warm-top modification is used for cloud tops warmer than −62°C. Three-hour outlooks are based on persistence and extrapolation and trend and expectancy guidelines. Verification results show the average error of the rainfall estimates for a storm total precipitation event is about30%.
TL;DR: In this article, the inadequacies of surface fluxes for use in numerical models of atmospheric flow are examined by assuming idealized spatial distributions of the Richardson number over a grid area.
Abstract: This study examines the inadequacies of formulations for surface fluxes for use in numerical models of atmospheric flow. The difficulty is that numerical models imply spatial averaging over each grid area. Existing formulations am based on the relationship between local fluxes and local gradients and appear to describe the relationship between the grid-averaged flux and the grid-averaged gradient poorly. For example, area-averaging the bulk aerodynamic relationship reveals additional spatial correlation terms and a complex relationship between the grid-averaged exchange coefficient and the stability based on “model” available” grid-averaged variables. This problem is studied by assuming idealized spatial distributions of the Richardson number over a grid area. Some perspective is provided by consulting observed spatial distributions of the layer Richardson number at the surface. Various contributions to the area-averaged surface flux are studied by employing a small-scale numerical model as a gri...
TL;DR: In this article, the authors analyzed the effect of model properties such as the projected initial perturbations onto gravity waves, the sweeping out of errors by correct or perfect lateral boundaries, and the reduction of differences by subgrid dissipation.
Abstract: Recently reported results indicate that limited-area mesoscale models with prescribed lateral boundaries do not exhibit the same predictability error growth as observed in large-scale (global) models. These results have been reanalyzed in greater detail. New methods of limited-area initialization and spectral analysis have been used. The new analyses indicate that several model properties act to restrict the growth of perturbation. These include: the Projection of initial perturbations onto gravity waves which interact only weakly with other, more significant motions; the “sweeping out” of errors by correct or perfect lateral boundaries; and the reduction of differences by subgrid dissipation. This last property suggests that there is a strong dynamical forcing of small scales by much larger scales, so that this forcing is only weakly affected by typical, small perturbations in this model. New experiments suggest that some quasi-geostrophic components of the forecasts, away from the inflow bounda...
TL;DR: In this paper, the authors investigate summertime droughts and heat waves in the Kansas City area and their associated large-scale circulation patterns and land-surface moisture conditions using climatological monthly mean surface data, rawinsonde data, and gridded 500 mb height data.
Abstract: Summertime droughts and/or heat waves in the Kansas City area and their associated large-scale circulation patterns and land-surface moisture conditions are investigates, using climatological monthly mean surface data, rawinsonde data. Palmer drought severity indices, gridded monthly mean sea-level pressure data, and gridded 500 mb height data. Surface station data include monthly mean surface pressure, maximum/minimum temperature, temperature range, monthly total precipitation, dewpoint and relative humidity. Anomalies in monthly mean surface air temperature at Kansas City are used as a basis for objectively ranking the 276 months in the 92 summers, 1889–1980. The concentration of drought months in the decades of the 1910s, 1930s, and 1950s is evident. Many of the hot months during these periods exhibited negative anomalies in relative humidity, dewpoint, precipitation and Palmer index. Not all the hot summer months in the record at Kansas City appear to have been associated with drought (as def...
TL;DR: In this article, an analysis of research aircraft observation, satellite total columnar ozone retrievals and synoptic upper-air soundings are used to describe the structure of Arctic jetstreams and their associated frontal zones and tropopause folds.
Abstract: Analyses of research aircraft observation, satellite total columnar ozone retrievals and synoptic upper-air soundings are used to describe the structure of Arctic jetstreams and their associated frontal zones and tropopause folds. These analyses document the presence of major tropopause folding events within the Arctic that occur at the flanks of large-scale (∼2000 km) polar vortices. One example shows a polar vortex and its associated tropopause fold and Arctic front that migrated from the high Canadian Arctic southward into midlatitudes over central North America. The frigid cold-air outbreak associated with this migration was an important component in the record setting daily minimum temperatures that were recorded from the Great Lakes to southern Florida. Total columnar ozone measurements from the Total Ozone Mapping Spectrometer (TOMS) are shown to identify the location of polar vortices and the mesoscale (∼200 km) ozone gradients at the flanks of these vortices which coincide with regions o...
TL;DR: In this paper, three years of three-hourly infrared satellite data from the American geostationary satellites were used to determine the large-scale spatial and temporal variations in the diurnal cycle of tropical convective precipitation.
Abstract: Three years of three-hourly infrared satellite data from the American geostationary satellites were used to determine the large-scale spatial and temporal variations in the diurnal cycle of tropical convective precipitation. The region examined extended from 50°N to 50°S, 175°E to 25°W. The satellite data were related to convection through the fractional coverage of 2.5° subareas by clouds colder than several threshold temperatures. Seasonal maps showing mean fractional coverage, total diurnal variance in cold clouds, as well as variance associated with the first and second harmonic, respectively, present the results. Seasonal maps showing vectors of the amplitude and phase of the first harmonic are also shown. In general, our results agreed with previous studies. The mean positions and annual variations of the maxima and minima in tropical convection were accurately depicted. The diurnal cycle over the tropical continents and the other continents during summer was much larger than that over the ...
TL;DR: In this article, a triply nested, movable mesh model was used to study the behavior of tropical cyclones encountering island mountain ranges, and it was found that the islands affected the basic flow as well as the wind field directly associated with the storm system.
Abstract: A triply nested, movable mesh model was used to study the behavior of tropical cyclones encountering island mountain ranges. The integration domain consisted of a 37° wide and 45° long channel, with an innermost mesh resolution of 1/6°. The storms used for this study were embedded in easterly flows of ∼5 and ∼10 m s−1 initially. Realistic distributions of island topography at 1/6° resolution were inserted into the model domain for the region of the Caribbean, including the islands of Cuba, Hispaniola, and Puerto Rico; the island of Taiwan; and the region of Luzon in the northern Philippines. It was found that the islands affected the basic flow as well as the wind field directly associated with the storm system. The combination of these effects caused changes in the track and translational speed of the storm. In particular, in the case of the 5 m s−1 easterly flow, the storm accelerated and veered to the north well before reaching Taiwan. For the other island distributions, the northward deflecti...
TL;DR: Aircraft, land station, and buoy data were composited with respect to the center of Hurricane Alicia (1983) for three 8-h periods corresponding to prelandfall in the open Gulf of Mexico, landfall in the Galveston area, and postlandfall near Houston as discussed by the authors.
Abstract: Aircraft, land station, and buoy data were composited with respect to the center of Hurricane Alicia (1983) for three 8-h periods corresponding to prelandfall in the open Gulf of Mexico, landfall in the Galveston area, and postlandfall in the vicinity of Houston. Comparison of the wind analyses before, during, and after landfall emphasizes the land-sea frictional asymmetry at landfall. In addition, other asymmetries in the surface wind field and differences between the flight-level and the surface wind fields are revealed. The asymmetric structure of the surface wind field may be interpreted as having resulted from the combined effects of land-sea roughness differences, background environmental flow, and storm translation. The land-sea frictional difference acted to oppose the mean vortex flow over land and reinforce it over water. The southwest background environmental flow acted nearly parallel to the coastline, producing surface inflow on the left side and outflow on the right side, while the ...