Showing papers in "Monthly Weather Review in 1992"
TL;DR: Results from several months of parallel testing with the NMC spectral model have been very encouraging, and favorable features include smoother analysis increments, greatly reduced changes from initialization, and significant improvement of 1-5-day forecasts.
Abstract: At the National Meteorological Center (NMC), a new analysis system is being extensively tested for possible use in the operational global data assimilation system. This analysis system is called the spectral statistical- interpolation (SSI) analysis system because the spectral coefficients used in the NMC spectral model are analyzed directly using the same basic equations as statistical (optimal) interpolation. Results from several months of parallel testing with the NMC spectral model have been very encouraging. Favorable features include smoother analysis increments, greatly reduced changes from initialization, and significant improvement of 1-5-day forecasts. Although the analysis is formulated as a variational problem, the objective function being minimized is formally the same one that forms the basis of all existing optimal interpolation schemes. This objective function is a combination of forecast and observation deviations from the desired analysis, weighted by the invent of the correspon...
1,890 citations
TL;DR: In this article, a simple implementation of the Arakawa and Schubert (1974) cumulus parameterization is presented, where the major simplification made is to "relax" the state toward equilibrium each time the parameterization was invoked, rather than requiring that the final state be balanced.
Abstract: A simple implementation of the Arakawa and Schubert (1974) cumulus parameterization is presented. The major simplification made is to 'relax' the state toward equilibrium each time the parameterization is invoked, rather than requiring that the final state be balanced, as in the original Arakawa-Schubert implementation. This relaxed Arakawa-Schubert (RAS) scheme is evaluated in off-line tests using the Global Atmospheric Research Program (GARP) Atlantic Tropical Experiment (GATE) Phase III data. The results show that RAS is equivalent to the standard implementation of Arakawa-Schubert but is more economical and simpler to code. RAS also avoids the ill-posed problem that occurs in Arakawa-Schubert as a result of having to solve for a balanced state.
1,050 citations
TL;DR: In this paper, a comprehensive scheme for the parameterization of radiative transfer in numerical weather prediction (NWP) models has been developed, which is based on the solution of the δ-two-stream version of the RTS equation incorporating the effects of scattering, absorption, and emission by cloud droplets, aerosols, and gases in each part of the spectrum.
Abstract: A comprehensive scheme for the parameterization of radiative transfer in numerical weather Prediction (NWP) models has been developed. The scheme is based on the solution of the δ-two-stream version of the radiative transfer equation incorporating the effects of scattering, absorption, and emission by cloud droplets, aerosols, and gases in each part of the spectrum. An extremely flexible treatment of clouds is obtained by allowing partial cloud cover in any model layer and relating the cloud optical properties to the cloud liquid water content. The latter quantity may either be a prognostic or diagnostic variable of the host model or specified a priori depending on cloud type, height, or similar criteria. The treatment of overlapping cloud layers is based on realistic assumptions, but any different approach requires only minor modifications of the code. The scheme has been tested extensively in the framework of the intercomparison of radiation codes in climate models (ICRCCM, WMO 1984, 1990). Rad...
789 citations
TL;DR: In this paper, a novel form of the Euler equations is developed through the use of a different vertical coordinate system, which is shown to take a form that parallels very closely the form of hydrostatic equations cast in isobaric coordinates.
Abstract: A novel form of the Euler equations is developed through the use of a different vertical coordinate system. It is shown that the use of hydrostatic pressure as an independent variable has the advantage that the Euler equations then take a form that parallels very closely the form of the hydrostatic equations cast in isobaric coordinates. This similarity holds even when topography is incorporated through a further transformation into terrain-following coordinates. This leads us to suggest that hydrostatic-pressure coordinates could be used advantageously in nonhydrostatic atmospheric models based on the fully compressible equations.
388 citations
TL;DR: In this paper, a simple method of eliminating spurious high-frequency oscillations is presented, which uses a digital filter applied to time series of the model variables generated by short-range forward and backward integrations from the initial time.
Abstract: Spurious high-frequency oscillations occur in forecasts made with the primitive equations if the initial fields of mass and wind are not in an appropriate state of balance with each other. These oscillations are due to gravity-inertia waves of unrealistically large amplitude; the primary purpose of initialization is the removal or reduction of this high-frequency noise by a delicate adjustment of the analyzed data. In this paper a simple method of eliminating spurious oscillations is presented. The method uses a digital filter applied to time series of the model variables generated by short-range forward and backward integrations from the initial time. The digital filtering technique is applied to initialize data for the High-Resolution Limited-Area Model (HIRLAM). The method is shown to have the three characteristics essential to any satisfactory initialization scheme: (i) high-frequency noise is effectively removed from the forecast; (ii) changes made to the analyzed fields are acceptably small...
296 citations
TL;DR: In this article, the authors proposed a hybrid approach for incorporating cumulus convection into mesoscale numerical models, which combines the traditional approach with explicit condensation at convectively stable points and fully explicit methods regardless of stability.
Abstract: Current approaches for incorporating cumulus convection into mesoscale numerical models are divided into three groups. The traditional approach utilizes cumulus parameterization at convectively unstable points and explicit (nonparameterized) condensation at convectively stable points, The fully explicit approach uses explicit methods regardless of stability. The hybrid approach parameterizes convective scale updrafts and downdrafts, but “detrains” a fraction of parameterized cloud and precipitation particles to the grid scale. This allows the path and phase changes of such particles to be explicitly predicted over subsequent time steps. The traditional approach provides the only alternative for numerical models with grid spacing too large to resolve mesoscale structure. As grid spacing falls below 50 km, the traditional approach becomes increasingly likely to violate fundamental scale-separation requirements of parameterization, particularly if mesoscale organization of convection is parameterize...
292 citations
Abstract: Lagged cross correlations between outgoing longwave radiation (OLR) and National Meteorological Center global analyses are utilized to isolate the preferred upper-level and surface circulation anomalies associated with tropical convection during northern winter. Three intraseasonal time scales are studied: 30–70, 14–30, and 6–14 days. In the 30–70-day band, the upper-level circulation signals are zonally elongated, with zonal wavenumbers 0–2 dominant. Higher-frequency signals are dominated by zonal wavenumbers 5 and 6. In the 14–30-day band, convection over the eastern hemisphere is associated with upper-level anticyclones in the subtropics and appears to be linked in some cases to midlatitude wave trains. The strongest signals are for convection over Africa, Australia, and the eastern Indian Ocean. Only weak signals are seen for convection over Indonesia. In these regions of upper-level easterlies, OLR anomalies peak prior to the maximum anomalies in wind, suggesting forcing of the circulation b...
289 citations
TL;DR: In this article, two limited-memory quasi-Newton minimization techniques were used to iteratively find the minimum of a cost function, with the NMC forecast as a constraint.
Abstract: Variational four-dimensional (4D) data assimilation is performed using an adiabatic version of the National Meteorological Center (NMC) baroclinic spectral primitive equation model with operationally analyzed fields as well as simulated datasets. Two limited-memory quasi-Newton minimization techniques were used to iteratively find the minimum of a cost function, with the NMC forecast as a constraint. The cost function consists of a weighted square sum of the differences between the model forecast and observations over a time interval. In all the experiments described in this paper, observations are available for all degrees of freedom of the model. The derivation of the adjoint of the discretized adiabatic NMC spectral model is presented. The creation of this adjoint model allows the gradient of the cost function with respect to the initial conditions to be computed using a single backward-in-time integration of the adjoint equations. As an initial evaluation of the variational data-assimilation ...
279 citations
TL;DR: In this paper, a detailed analysis of the Klemp and Wilhelmson (KW) explicit technique for integrating the time-split nonhydrostatic system is undertaken, and it is found that the interaction between propagating and advecting acoustic modes can introduce severe constraints on the maximum allowable time steps proper filtering can remove these constraints.
Abstract: The mathematical equivalence of the linearized two-dimensional (2D) shallow-water system and the 2D acoustic-advection system strongly suggests that time-split schemes designed for the hydrostatic equations can be employed in nonhydrostatic models and vice versa Stability analyses are presented for several time-split numerical methods for integrating the two systems The primary interest is in the nonhydrostatic system and in explicit numerical schemes where no multidimensional elliptic equations arise; thus, a detailed analysis of the Klemp and Wilhelmson (KW) explicit technique for integrating the time-split nonhydrostatic system is undertaken It is found that the interaction between propagating and advecting acoustic modes can introduce severe constraints on the maximum allowable time steps Proper filtering can remove these constraints Other explicit time-split schemes are analysed, and, of all the explicit schemes considered, it is believed that the KW time-split method offers the best co
239 citations
TL;DR: In this paper, the authors proposed a method of formulating equitable skill scores for categorical forecasts of nominal and ordinal variables, which are based on scoring matrices, which assign scores to the various combinations of forecast and observed events.
Abstract: Many skill scores used to evaluate categorical forecasts of discrete variables are inequitable, in the sense that constant forecasts of some events lead to better scores than constant forecasts of other events. Inequitable skill scores may encourage forecasters to favor some events at the expense of other events, thereby producing forecasts that exhibit systematic biases or other undesirable characteristics. This Paper describes a method of formulating equitable skill scores for categorical forecasts of nominal and ordinal variables. Equitable skill scores are based on scoring matrices, which assign scores to the various combinations of forecast and observed events. The basic tenets of equitability require that (i) all constant forecasts—and random forecosts—receive the same expected score, and (ii) the elements of scoring matrices do not depend on the elements of performance matrices. Scoring matrices are assumed here to be symmetric and to possess other reasonable properties related to the natu...
209 citations
TL;DR: In this paper, a three-dimensional nonhydrostatic mesoscale model is designed to optimally represent the scale-interaction process among inertially balanced and unbalanced modes occurring within convective weather systems.
Abstract: A three-dimensional nonhydrostatic mesoscale model is presented that is designed to optimally represent the scale-interaction process among inertially balanced and unbalanced modes occurring within convective weather systems. Because scale-interaction simulations are long-term integrations that emphasize the evolution of the three-dimensional kinetic energy spectrum, the model is built to conserve enstrophy, as well as kinetic energy against numerical sources and sinks in three dimensions. A non-Boussinesq and quasi-compressible framework is employed to maintain applicability on meso-α and larger scales as well as for situations of relatively large local density variation. Sample integrations in two and three dimensions are presented that show enstrophy conservation to be effective in improving the prediction of nonlinear evolution as truncation errors act to force anomalous bifurcations from the physical solution.
TL;DR: In this article, an adjoint of the Pennsylvania State University-National Center for Atmospheric Research (PSU-NCAR) Mesoscale Model has been developed for use in sensitivity analysis following Cacuci.
Abstract: An adjoint of the Pennsylvania State University-National Center for Atmospheric Research (PSU-NCAR) Mesoscale Model has been developed for use in sensitivity analysis following Cacuci. Sensitivity analysis is defined as the determination of the potential impact on some quantitative measure of a forecast aspect due to arbitrary perturbations of the model dynamic fields at earlier times. Input to the adjoint operator is the gradient of the forecast-aspect measure with respect to the model fields at the verification time, and output is the corresponding gradients defined at earlier times. The adjoint is exactly determined from a tangent linear model, which is itself an approximation to the dry nonlinear model. This approximation is shown to be accurate even when evaluated with regard to the moist nonlinear model for periods up to 36 h, although this accuracy is necessarily case and perturbation dependent. The mathematics describing the scheme are applied to the model in its spatially and temporally ...
TL;DR: In this paper, a low-resolution Geophysical Fluid Dynamics Laboratory (GFDL) general circulation model has been integrated for 15 years, and the output from this model run was used to investigate the influence of El Nin-Southern Oscillation (ENSO) events on the variability of tropical-storm formation.
Abstract: A low-resolution Geophysical Fluid Dynamics Laboratory (GFDL) general circulation model has been integrated for 15 years. In the course of this experiment, the observed month-to-month sea surface temperature (SST) variations in the tropical Pacific Ocean were incorporated in the lower boundary condition. The output from this model run was used to investigate the influence of El Nin-Southern Oscillation (ENSO) events on the variability of tropical-storm formation. Criteria for detecting tropical cyclogenesis and tropical-storm formation were developed for the model. Tropical storms appearing in the model atmosphere exhibit many typhoonlike characteristics: strong cyclonic vorticity and convergence in the lower troposphere, strong anticyclonic vorticity and divergence near the tropopause, and intense precipitation. It is demonstrated that, despite its coarse resolution, the model is capable of reproducing the observed geographical distribution and seasonal variation of tropical-storm formation. The...
TL;DR: In this article, the authors examined multiscale variabilities in the atmosphere over the tropical western Pacific during the 1979 Northern Hemisphere winter in order to identify possible interactions between phenomena of different spatial and temporal scales.
Abstract: The paper examines multiscale variabilities in the atmosphere over the tropical western Pacific during the 1979 Northern Hemisphere winter in order to identify possible interactions between phenomena of different spatial and temporal scales. Based on the convection-index information derived from satellite measurements, two intraseasonal oscillations (ISOs), accompanied by both rotational and divergent circulations, propagate eastward from the Indian Ocean to the western Pacific. Over the warm pool in the western Pacific, the ISOs develop into quasi-stationary systems with an enhanced rotational circulation characterized by a strong westerly jet in the lower troposphere and western Pacific region.
TL;DR: The utility of signal detection theory is illustrated, how it can be used to understand the effects of time pressure created by frequent weather activity on forecasting judgments, and how to achieve a specific social policy are illustrated.
Abstract: A variety of measures are used to judge the skill and accuracy with which forecasters predict the weather and to verify forecasts: Such measures can confound accuracy with decision strategy and sometimes give conflicting indications of performance. Signal detection theory (SDT) provides a theoretical framework for describing forecasting behavior and minimizing these problems. We illustrate the utility of signal detection theory in this context, show how it can be used to understand the effects of time pressure created by frequent weather activity on forecasting judgments, and illustrate how to achieve a specific social policy.
TL;DR: In this article, a composite meteorological field was constructed using European Centre for Medium-Range Weather Forecasts (ECMWF) analyses for the northern summers of 1980-1987 for the tropical western Pacific, Bay of Bengal-northeastern India, and African Atlantic regions.
Abstract: Periods of enhanced synoptic activity in the tropical western Pacific, Bay of Bengal-northeastern India, and African-Atlantic regions are identified by extended empirical orthogonal function analysis. Composite mete-orological fields for such active periods at various sites are constructed using European Centre for Medium-Range Weather Forecasts (ECMWF) analyses for the northern summers of 1980–1987. These composite data form the basis for evaluating the contributions of different dynamical processes to local balances of beat, moisture, vorticity, enstrophy, and energy, so that the propagation dynamics and principal energy sources of the tropical disturbances may be studied in detail. In all three tropical regions considered here, the westward propagation of the synoptic-scale disturbances is attributed mostly to vorticity advection by both the time-mean flow and the transient fluctuations. In the western Pacific and Indian sectors, condensation heating associated with cumulus convection is seen ...
TL;DR: In this article, a method to convert conventional semi-Lagrangian schemes into quasi-monotone schemes is presented, and numerical examples with linear and nonlinear transport equations demonstrate the ability of modified semi-lagrangians to better maintain the shape of the solution in the presence of shocks and discontinuities.
Abstract: A method to convert conventional semi-Lagrangian schemes into quasi-monotone schemes is given Numerical examples with linear and nonlinear transport equations demonstrate the ability of our modified semi-Lagrangian schemes to better maintain the shape of the solution in the presence of shocks and discontinuities
TL;DR: In this article, the authors examined the initiation of a line of thunderstorms that developed along a preexisting, quasi-stationary boundary-layer convergence line on 17 July 1987.
Abstract: The initiation of thunderstorms is examined through a combined observational and modeling case study. The study is based on Doppler radar, aircraft, mesonet, balloon sounding, and profiler and photographic data from the Convection Initiation and Downburst Experiment (CINDE) conducted near Denver, Colorado. The study examines the initiation of a line of thunderstorms that developed along a preexisting, quasi-stationary boundary-layer convergence line on 17 July 1987. The storms were triggered at the intersection of the convergence line with horizontal rolls where enhanced updrafts were present. The primary effect of the convergence line was to deepen the moist layer locally and provide a region potentially favorable to deep convection. The critical factor governing the time of storm development was apparently related to the attainment of a balance between horizontal vorticity in the opposing flows on either side of the convergence line. The effect was to cause the updrafts in the convergence line ...
TL;DR: In this paper, statistical evidence is presented to support the notion that tropical convection in the eastern Pacific and Atlantic intertropical convergence zone (ITCZ) during northern winter can be forced by disturbances originating in the extratropics.
Abstract: Statistical evidence is presented to support the notion that tropical convection in the eastern Pacific and Atlantic intertropical convergence zone (ITCZ) during northern winter can be forced by disturbances originating in the extratropics. The synoptic-scale transients in these regions are characterized at upper levels by strong positive tilts in the horizontal and appear to induce vertical motions ahead of troughs as in midlatitude baroclinic systems. Two case studies of such interactions are examined, one for the eastern North Pacific ITCZ and another somewhat different type of interaction for the South Pacific convergence zone (SPCZ) over the western South Pacific. Both cases are associated with upper-level troughs, strong cold advection deep into the tropics, and the formation of a frontal boundary at low levels. The ITCZ case is characterized by the advection of anomalously high isentropic potential vorticity air southward, a strong poleward flux of heat and westerly momentum, and the devel...
TL;DR: The outer eyewall of Hurricane Gilbert of 1988 formed an outer eywall as it intensified rapidly toward a record minimum pressure of 888 hPa in the western Caribbean, while the inner eyewalls showed some signs of weakening before landfall on the Yucatan Peninsula as discussed by the authors.
Abstract: Hurricane Gilbert of 1988 formed an outer eyewall as it intensified rapidly toward a record minimum pressure of 888 hPa in the western Caribbean. The outer eyewall strengthened and contracted, while the inner eyewall showed some signs of weakening before landfall on the Yucatan Peninsula. Remarkably, both eyewalls survived passage over land, but the storm was much weaker when it entered the Gulf of Mexico. Although the primary cause of weakening was passage over land, the effect of the contracting outer eyewall may have contributed. Later, the outer eyewall completely replaced the inner eyewall. Subsequently, it contracted steadily but slowly as Gilbert maintained nearly constant intensity over the cooler waters of the Gulf before final landfall on the mainland of Mexico.
TL;DR: In this article, the authors investigated the dynamics of cyclone development over the midwestern United States on 15 December 1987 with a focus on the relationship between cyclone structure and condensational heating.
Abstract: The dynamics of a cyclone development over the midwestern United States on 15 December 1987 are investigated with a focus on the relationship between cyclone structure and condensational heating. Low-level cyclogenesis is initiated by a large-amplitude tropopause perturbation that develops over western North America. Using potential-vorticity (PV) inversion diagnostics, we show how the near-surface winds associated with this upper disturbance create a localized, warm, thermal anomaly within a surface baroclinic zone. The distribution of precipitation and the diabatic generation of a positive low-level PV feature near the cyclone center are also controlled by the tropopause perturbation. Development culminates in a superposition of positive anomalies of tropopause PV, moisture-induc6d PV, and surface potential temperature θ, with contributions to the total low-level circulation being about 30%, 20%, and 50%, respectively. This case is compared with a different cyclogenesis event (4–5 February 1988...
TL;DR: The 1991 hurricane season in the Atlantic basin featured 73 tropical waves (also known as African waves), most of which were relatively weak as mentioned in this paper, generating fewer than normal Atlantic tropical cyclones: seven tropical depressions of which only three intensified into tropical storms.
Abstract: The 1991 hurricane season in the Atlantic basin featured 73 tropical waves (also known as African waves), most of which were relatively weak. These waves generated fewer than normal Atlantic tropical cyclones: seven tropical depressions, of which only three intensified into tropical storms. Remarkably, none of these systems became hurricanes. The remainder of the Atlantic tropical cyclones formed from other sources. African waves triggered nearly all of the eastern Pacific tropical cyclones in 1991.
TL;DR: In this paper, the authors studied the teleconnections of the stream function in the global domain based on ECMWF 250-mb winds for the 11 northern winters from 1978/79 through 1988/89.
Abstract: Teleconnections of the streamfunction in the global domain based on ECMWF 250-mb winds for the 11 northern winters from 1978/79 through 1988/89 are documented in this study. A zonal structure with a node near the equator, indicating an out-of-phase relationship between the streamfunctions in the Northern and Southern hemisphere, appears to mask the fluctuations of the asymmetric components of streamfunction. After removing zonal means, a global pattern emerges as the dominant structure in the low-frequency band. This pattern consists of several dipoles straddling either the exit region of midlatitude jets or the equator, indicating the existence of teleconnections not only between the midlatitudes and the tropics but also between the Northern and Southern hemispheres. Teleconnection patterns in the intermediate-frequency band are predominantly wavelike. Seven waveguides are identified based on the one-point lag-correlation maps for base points near the maximum teleconnectivity. Among them are thr...
TL;DR: The continuous dynamic grid adaption (CDGA) technique developed in astrophysics and aeronautics is applied, to the best of our knowledge, to meteorological modeling as discussed by the authors.
Abstract: The continuous dynamic grid adaption (CDGA) technique developed in astrophysics and aeronautics is applied, to our knowledge, for the first time to meteorological modeling. The aim of CDGA is to improve the accuracy of numerical solutions of partial differential equations (typically those governing fluid flow) by the use of nonuniform grids that have higher local resolution in regions where the numerical error is presumed to be large. Conceptually, CDGA has some relationship to the well-known technique of grid stretching, but its power lies in its ability to determine an appropriate spatial distribution of grid points automatically and to update this distribution in response to changes in the evolving numerical solution. Application of the technique is facilitated by transforming the governing equations from physical space in which the grid is nonuniform, nonorthogonal and for which the individual grid points are in continuous motion to computational space, which by definition has both a regular ...
TL;DR: In this paper, three different interpolation methods are compared for a network of 111 long-term precipitation stations in Arizona and New Mexico, and the ability of the different methods to interpolate for known monthly precipitation totals is assessed by season and for the 19th- and 20th-century data separately.
Abstract: Three different interpolation methods are compared for a network of 111 long-term precipitation stations in Arizona and New Mexico. The methods studied are 1) multiple discriminant analysis (MDA), which is based on empirical orthogonal functions (E0Fs), 2) multiple linear regression (MLR), which is similar to Gandin's optimal interpolation, and 3) the normal ratio method. The MDA method is described in detail since it represents a novel use of EOF. The ability of the different methods to interpolate for known monthly precipitation totals is assessed by season and for the 19th- and 20th-century data separately. The MDA method is found to provide the most skillful interpolation for the sparse 19th-century network of stations and for the summer (June–July–August) season, which is characterized by mesoscale convection. A median model based on the three individual models is analyzed and found to be superior to the individual methods for the 20th-century network except for the summer season.
TL;DR: This article examined many surface-level meteorological variables (at standard shelter height, representing surface-layer conditions) during the time of spring leafing in order to detect other changes and to further analyze the cause, extent, and persistence of t...
Abstract: Current vegetation models hold constant the dynamics of seasonal biospheric changes, neglecting annual variability. One of these features, the spring “green wave” (onset of leafing or “grean-up”) in midiatitudes, is an example of the complex feedback loop between the atmosphere and plant communities. The green wave responds to the atmosphere, but, in turn, leafing causes rapid changes in the surface-layer energy budget. Annual variability tends to obscure the magnitude of the green wave's effects on conventional climatic records. When meteorological data are “normalized” to the green wave (averaged relative to first-leaf phonology data rather than to calendar date), an actual break in the spring maximum temperature curve can be detected. This project examined many surface-level meteorological variables (at standard shelter height, representing surface-layer conditions) during the time of spring leafing in order to detect other changes and to further analyze the cause, extent, and persistence of t...
TL;DR: In this paper, high spatial and temporal resolution fields generated by a mesoscale prediction model are used to study a case of rapid marine cyclogenesis within the context of potential vorticity (PV) thinking.
Abstract: High spatial and temporal resolution fields generated by a mesoscale prediction model are used to study a case of rapid marine cyclogenesis (26 mb in 12 h) within the context of potential vorticity (PV) thinking. The case, which occurred on 23 February 1987 near the east coast of the United States, was well simulated by the model, as was verified by ship reports and satellite imagery. Three components of the cyclone were investigated: 1) a surface thermal anomaly (or surrogate PV anomaly), 2) a low-level, diabatically produced PV anomaly in and near the frontal cloud band, and 3) a dry PV anomaly of upper-tropospheric and lower-stratosphoric origin. Trajectory tracing revealed that the surface thermal anomaly was caused primarily by northward transport of warm air into the central region of the low. Although surface sensible heat flux also contributed to the warm anomaly, a sensitivity experiment, run with the flux withheld, showed that it had little impact on the depth of the storm. Furthermore,...
TL;DR: In this paper, a cold-air outflow from thunderstorms over Illinois and Missouri propagated through the MIST (Microburst and Severe Thunderstorm) network over northern Alabama.
Abstract: On 13 July 1986 a cold-air outflow from thunderstorms over Illinois and Missouri propagated through the MIST (Microburst and Severe Thunderstorm) network over northern Alabama. The study of this outflow is important since the gust front was solely responsible for the initiation of numerous convective cells. Previous studies have documented the initiation of convection due to colliding gust fronts. In addition, there was a pronounced mesoscale organization of the cells atop the outflow boundary. This was most likely due to a combination of Kelvin–Helmholtz (K–H) and internal gravity (IG) wave activity. In contrast to previous cases, the K–H wave crests were oriented nearly perpendicular to the gust front within the analysis area. The resulting intersections between the circulations associated with the K–H waves and the gust front produced favorable locations for the initiation of convection. Subsequently, the convective cells remained along the updraft side of the K–H wave circulations as they pro...
TL;DR: In this paper, a specific formula for the general multiple-category scoring matrix is presented and proven to satisfy the necessary conditions for "equitability", which is compatible with a logical condensation of the general K-category problem into a set of K−1 two-category problems.
Abstract: Gandin and Murphy introduced an “equitable skill score” for use in evaluating categorical forecasts. For forecasts involving more than two categories, the elements of the scoring matrix are not defined uniquely. In this note, a specific formula for the general multiple-category scoring matrix is presented and proven to satisfy the necessary conditions for “equitability.” It is shown that, while it is not the only possible scoring matrix satisfying these necessary conditions, it is compatible with a logical condensation of the general K-category problem into a set of K−1 two-category problems. Each of the two-category problems is associated with one of the K−1 partitions defining the categories of the original problem.
TL;DR: In this paper, the authors studied the climatology of cyclogenesis off the east Asian coast based on 30 years (1958-87) of surface analyses and found two favorable areas for explosive deepening, one over the eastern Sea of Japan, and the other over the northwestern Pacific, east and southeast of Japan.
Abstract: The climatology of explosive cyclogenesis off the east Asian coast was studied, based on 30 years (1958–87) of surface analyses. There were two favorable areas for explosive deepening, one over the eastern Sea of Japan, and the other over the northwestern Pacific, east and southeast of Japan. The latter was located close to the warm Kuroshio Current. The frequency of explosive cyclogenesis reached a local minimum over Japan. The geographic distribution of explosive-cyclone frequency suggests that the explosive cyclogenesis is influenced by the Japanese islands. In addition, a positive correlation is found between explosive-cyclogenesis frequency and the El Nino episodes during 1958–87. The physical relationship between these two phenomena, however, is not well understood.