Storm Parameters Research Articles

Rainfall estimation and ground clutter rejection with dual polarization weather radar

Abstract. Conventional radars, used for atmospheric remote sensing, usually operate at a single polarization and frequency to estimate storm parameters such as rainfallrate and water content. Because of the high variability of the drop size distribution conventional radars do not succeed in obtaining detailed information because they just use horizontal reflectivity. The potentiality of the dual-polarized weather radar is investigated, in order to reject the ground-clutter, using differential reflectivity. In this light, a radar meteorology campaign was conducted over the city of Rome (Italy), collecting measurements by the polarimetric Doppler radar Polar 55C and by a raingauge network. The goodness of the results is tested by comparison of radar rainfall estimates with raingauges rainfall measurements.

Structure of magnetic fields in NOAA active regions 0486 and 0501 and in the associated interplanetary ejecta

Spectacular burst of solar activity in October–November 2003, when large solar spots and intense solar flares dominated the solar surface for many consecutive days, caused intense geomagnetic storms. In this paper we analyze solar and interplanetary magnetic fields associated with the storms in October–November 2003. We used space‐ and ground‐based data in order to compare the orientations of the magnetic fields on the solar surface and at 1 AU as well as to estimate parameters of geomagnetic storms during this violent period of geomagnetic activity. Our study further supports earlier reports on the correlation between the coronal mass ejection speed and the strength of the magnetic field in an interplanetary ejecta. A good correspondence was also found between directions of the helical magnetic fields in interplanetary ejecta and in the source active regions. These findings are quite significant in terms of their potential to predict the severity of geomagnetic activity 1–2 days in advance, immediately after an Earth directed solar eruption.

The Theory of Trapped-Fetch Waves with Tropical Cyclones—An Operational Perspective

Abstract The majority of high wave events and almost all cases of extreme or phenomenal wave growth are the result of a high degree of synchronicity between moving storms and the waves that they generate. This wave containment or resonance phenomenon, referred to as trapped-fetch waves, has been known for generations, but not always well understood by forecasters. The twofold threat of trapped-fetch waves is that they have the potential for extreme growth, yet are unheralded by leading swell. Conceptual and numerical Lagrangian reference frame experiments on wave containment are presented, illustrating the influence on tropical cyclone ocean waves by three storm parameters: storm speed, wind speed, and fetch length. To further illustrate the concepts and provide real-time application, a simple, desktop Lagrangian trapped-fetch wave model, used for training and operational assessment of trapped-fetch waves, is described in a companion article.

North Atlantic Hurricanes 1977–99: Surface Hurricane-Force Wind Radii

Abstract The Hurricane Research Division (NOAA/AMOL/HRD) flight-level data archive of 1977–99 North Atlantic hurricanes is used to create radial profiles of earth-relative surface wind speeds. Radii of hurricane-force winds are determined directly from these generated profiles. The distributions of hurricane-force wind radii stratified by minimum central pressure and quadrant, relative to the direction of storm motion, indicate marked variability among storms. However, a model which uses storm parameters to predict the radius of hurricane-force winds in a given quadrant of a hurricane does seem feasible. Roughly three-quarters of the variance in the hurricane- force wind radii of minimal hurricanes and about one-half of the variance in the hurricane-force wind radii of major hurricanes is explained by parameters of the storm, enough to make a predictive model of significant value. In addition, cumulative two-dimensional probability distributions of hurricane-force wind radii may have some utility for hurr...

Effect of Uncertainties in Modeling Tropical Cyclones on Pricing of Catastrophe Bonds:A Case Study

The insurance industry, in general, accepts large risks due to the combined severity and frequency of catastrophic events; further, these risks are poorly defined given the small amount of data available for extreme events. It is important for the equitable transfer of risk to understand and quantify this risk as accurately as possible. As this risk is propagated to the capital markets, more and more parties will be exposed. An important part of pricing insurance‐linked securities (ILS) is quantifying the uncertainties existing in the physical parameters of the catastrophe models, including both the hazard and damage models. Given the amount of reliable data (1945 till present) on important storm parameters such as central pressure drop, radius to maximum winds, and non‐stationarity of the occurrence rate, moments estimated for these parameters are not highly reliable and knowledge uncertainty must be considered. Also, the engineering damage model for a given class of building in a large portfolio is subject to uncertainty associated with the quality of the buildings. A sample portfolio is used to demonstrate the impact of these knowledge uncertainties. Uncertainties associated with variability of statistics on central pressure drop, occurrence rate, and building quality were estimated and later propagated through a tropical cyclone catastrophe model to quantify the uncertainty of PML results. Finally their effect on the pricing of a typical insurance‐linked security (ILS) was estimated. Statistics of spread over LIBOR given different bond ratings/probability of attachment are presented using a pricing model (Lane [2000]). For a typical ILS, a relatively large coefficient of variation for both probability of attachment and spread over LIBOR was observed. This in turn leads to a rather large price uncertainty for a typical layer and may explain why rational investors expect a higher return for assuming catastrophe risk. The results hold independent of pricing model used. The objective of this study is to quantify this uncertainty for a simple call option and demonstrate its effect on pricing.

Estimation of wind speed and wave height during cyclones

Wave and wind characteristics based on the cyclones, in the vicinity of the Nagapattinam coastline (east coast of India) were estimated. In all, 11 cyclones have crossed near the study region during 1960–1996. For the four severe cyclones, the isobaric charts were collected at three hourly intervals from the India Meteorological Department. The storm variables such as central pressure, radius of maximum wind, speed of forward motion and direction of storm movement were extracted and the method based on standard Hydromet pressure profile, were used for the hindcast of storm wind fields. For all the cyclones the maximum significant wave height within the storm and its associated spectral peak period was estimated using the Young’s model considering the moving wind field and the results are compared with the hurricane wave prediction techniques provided in the shore protection manual published by the US Army Corps of Engineers in 1984. The study shows that the estimated wind speed and the data reported by ships were comparable. Empirical expressions relating wind speed, wave height and wave period to storm parameters were derived. The design wave height for different return periods was obtained by fitting a two-parameter Weibull distribution to the estimated significant wave heights. The design wave height was 9.39 m for 1 in 100 year return period for a direct hit of cyclone.

Noteworthy C-band radar parameters of storms on hail days in northwestern Spain

The data provided by a meteorological C-band radar have been employed in order to analyze the behavior of 224 storms that occurred on hail days in the provinces of León and Zamora, in the northwest of Spain. A network of more than 700 voluntary observers supplied the necessary information to distinguish hailstorms from storms that did not produce hail precipitation. The observers also reported the size of the hailstones found. Among the variables studied are the maximum reflectivity factors, the vertical developments, and the motion speed of the storm for hailstorms as well as for storms with no hail. The altitude at which the precipitation processes take place inside the storm cell and its average lifetime are the variables that determine the subsequent evolution of hailstorms and no-hail storms in the same day. Furthermore, these variables have been analyzed taking into account the type of storm: unicellular, multicellular or supercellular. Finally, a correlation between the characteristics of the storms and the size of the hailstones registered simultaneously on the ground has been searched for using the RHI detected on the radar exactly at the time of the precipitation.

Measurement of Equivalent Dielectric Parameters of Sandstorms from the Microwave Attenuation

The theory is presented for one method of determining the equivalent dielectric parameters of sand storms from microwave propagation measurement over a line of sight link. The method required the transmission of linear polarized or circle-polarized signal and attenuation measurement. The equivalent dielectric parameters of sandstorms determined at frequencies of 33.5 GHz and 93 GHz over a terrestrial link.

Estimation of Convective Rainfall from Lightning Observations

Abstract The objective of this study is to develop a technique to use lightning observations for estimating convective rainfall. A framework for rainfall estimation is developed in which key elements are 1) the rainfall–lightning ratio, that is, the convective rainfall mass per cloud-to-ground lightning flash; 2) the spatial distribution of rainfall relative to flash locations; and 3) the temporal distribution of rainfall relative to the time of lightning occurrence. These three elements are examined through a study of 22 summer thunderstorms in the domain covered by the Melbourne, Florida, WSR-88D radar during August of 1992 and 1993. The analyses are carried out by combining lightning observations from the National Lightning Detection Network with storm parameters computed from 3D reflectivity observations using the Thunderstorm Identification Tracking and Nowcasting storm-tracking and analysis algorithms. The effect of the prevailing convective regime on the variability of lightning–rainfall relationsh...

Geomagnetic storms, the Dst ring-current myth and lognormal distributions

The definition of geomagnetic storms dates back to the turn of the century when researchers recognized the unique shape of the H-component field change upon averaging storms recorded at low latitude observatories. A generally accepted modeling of the storm field sources as a magnetospheric ring current was settled about 30 years ago at the start of space exploration and the discovery of the Van Allen belt of particles encircling the Earth. The Dst global ‘ring-current’ index of geomagnetic disturbances, formulated in that period, is still taken to be the definitive representation for geomagnetic storms. Dst indices, or data from many world observatories processed in a fashion paralleling the index, are used widely by researchers relying on the assumption of such a magnetospheric current-ring depiction. Recent in situ measurements by satellites passing through the ring-current region and computations with disturbed magnetosphere models show that the Dst storm is not solely a main-phase, growth to disintegration, of a massive current encircling the Earth. Although a ring current certainly exists during a storm, there are many other field contributions at the middle-and low-latitude observatories that are summed to show the ‘storm’ characteristic behavior in Dst at these observatories. One characteristic of the storm field form at middle and low latitudes is that Dst exhibits a lognormal distribution shape when plotted as the hourly value amplitude in each time range. Such distributions, common in nature, arise when there are many contributors to a measurement or when the measurement is a result of a connected series of statistical processes. The amplitude-time displays of Dst are thought to occur because the many time-series processes that are added to form Dst all have their own characteristic distribution in time. By transforming the Dst time display into the equivalent normal distribution, it is shown that a storm recovery can be predicted with remarkable accuracy from measurements made during the Dst growth phase. In the lognormal formulation, the mean, standard deviation and field count within standard deviation limits become definitive Dst storm parameters.

Empirical Simulation Technique Based Storm Surge Frequency Analyses

This paper describes theory and application of the empirical simulation technique (EST), a statistical procedure for simulating time series and frequency-of-occurrence relationships for nondeterministic multiparameter systems. Procedures described are applied to a storm surge analysis for tropical events along the coast of Delaware. The approach involves the numerical simulation of historical events, the analysis of the parameters associated with each event, the application of the EST to that data, and the generation of frequency-of-occurrence relationships for 40 locations within the study area. The development of the input data set of descriptive storm parameters and their respective responses require the use of planetary boundary layer and very large domain hydrodynamic modeling techniques. Development of this input database is described herein. Implementation of the EST is based on N repetitions of T -year simulations; therefore, mean-value frequency relationships are computed and assigned confidence ...

Vegetative Filter Strip Design for Grassed Areas Treated with Animal Manures

Vegetative filter strips (VFS) are a low-cost management option that have been demonstrated to be effective in reducing runoff transport of fertilizer constituents applied to grassed areas (pasture or meadow). Runoff quality studies involving fertilizers applied to grassed areas suggest that VFS can be designed by assuming that (1) only infiltration is responsible for pollutant removal, (2) the first post-application runoff event is most important from a water quality perspective (enabling a design event approach), and (3) no pollutant build-up that degrades VFS performance will occur. The purpose of this study was to develop a VFS design algorithm for grassed areas that uses available information on the water quality dynamics of these systems to simplify the design process to the greatest degree practical. The design algorithm consists of the SCS (1972) Curve Number method for runoff estimation and the Overcash et al. (1981) equation for predicting concentrations of pollutants exiting a VFS as a function of VFS and runoff parameters. The procedure can be used to determine the VFS length required to meet either an allowable pollutant runoff concentration or allowable pollutant mass transport. As an alternative, the process can be used to determine VFS length required to achieve given relative reductions in incoming pollutant runoff concentrations and mass transport. This algorithm can be used quickly and with minimal data to determine the VFS length requirement necessary to provide any desired degree of effectiveness given inputs such as incoming pollutant runoff concentration, background pollutant runoff concentration, soil hydrologic properties, and design storm parameters. Charts are presented that eliminate the need for computations in selected cases.

A Continuous Simulation Approach to Design Storm Calibration

The paper suggests the opportunity to calibrate the design storm parameters and associated antecedent soil wetness conditions for each climatic situation of interest on the basis of the results obtained by means of a continuous simulation of catchment response, extended to a sufficiently wide spectrum of catchment characteristics. Assuming a suitable model to represent catchment response, calibration was performed by direct comparison between the peak flow probability distributions derived from design storm application and the related frequency distributions obtained through continuous simulation, in order to reach a reasonable agreement between the two. The results show that this methodological approach is fully satisfactory. Generally speaking, the synthetic storm parameters appear to be quite dependent on catchment loss characteristics, and especially on potential infiltration, but are almost insensitive to pervious soil percentage and to other factors related to net rainfall catchment response. For practical purposes, similar calibrations should be performed with reference to the main climatic situations of each region of interest. In this way the results could be applied, under similitude assumptions, to any specific location where detailed rainfall information is lacking or insufficient.

Shelf-sea response to tropical storms along the west coast of Mexico

The shelf-sea response to tropical storms along the west coast of Mexico is investigated using a layered ocean model forced by a travelling circular storm. Simulations using a straight coastline with a narrow continental shelf show that the response is typified by a cyclonic eddy along the storm track with inertial oscillations in the deep ocean and a trapped wave pulse at the coast. The coastal wave has typical phase speeds of 1.5–2.0 m s −1, alongshore scales of 500–1000 km, and cross-shore scales of 100–200 km. Test runs indicate that the coastal response is a function primarily of the intensity and duration of alongshore winds near the coast, and of the propagation speed of the storm relative to the free coastal-trapped wave phase speed. Atmospheric pressure anomalies appear to play a minor role in generating the coastal wave. Model runs using realistic bathymetry and storm parameters for two hurricanes during the summer of 1984 are compared with current, temperature and pressure observations in the Gulf of California. The model results are in good agreement with observed wave properties with typical surface displacements of 20 cm, alongshore current speeds of 0.5 m s −1, and upper interface displacements of 30 m. Wave generation for the two 1984 storms occurs primarily in the vicinity of Cabo Corrientes where storm winds are reported to be the strongest. The cape geometry in this region may also contribute to the enhanced response.

Millimeter wave propagation in arid land-a field study in Riyadh

A field study on wave propagation has been actively running for four years in Riyadh, Saudi Arabia. The study involves the operation and monitoring of two links at a frequency of 40 GHz, and an infrared link at 0.88- mu m wavelength. A meteorological station is also operated and monitored. The effect of sand storms on propagation is studied by measuring storm parameters, namely, visibility, particle size and size distribution, and induced attenuation. The results are compared with long-term visibility data for Riyadh, and a complete statistical analysis is given. The effect of rain is studied by measuring both rain rate and rain attenuation. Long-term rain data are utilized to derive long-term rain statistics. It is shown that the measured attenuation due to sand storms is about four times larger than the calculated attenuation at 40 GHz. The measured rain attenuation at infrared is found to be smaller by a factor of 0.3 than theoretically predicted attenuation.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

Multidimensional Rainfall Parameter Estimation from Sparse Network

The multidimensional precipitation model proposed by Waymire et al. provides realistic representations of the rainfall process. The model, however, in its most simplified form requires the numerical evaluation of nine parameters. Islam et al. developed a parameter estimation procedure and they applied the methodology to a small experimental basin with a dense network of rain gauges. In this paper the same estimation procedure is attempted over a larger area where only a sparse rain‐gauge network is available. Parameter estimates are determined for cyclonic‐midlatitude and convective storms, which are characteristic of the winter and summer rain seasons over the test basin. Using the seasonal storm parameter estimates, multidimensional model storms are generated over the Brazos Valley in Texas, and the storms are assessed qualitatively.

Free Surface Effects on the Near-Inertial Ocean Current Response to a Hurricane

Abstract During the passage of hurricane Frederic in 1979, four ocean current meter arrays in water depths of 100–950 m detected both a baroclinic and a depth-independent response in the near-inertial frequency band. Although the oceanic response was predominately baroclinic, the hurricane excited a depth-independent component of 5–11 cm s−1. The origin and role of the depth-independent component of velocity is investigated using a linear analytical model and numerical simulations from a 17-level primitive equation model with a free surface. Both models are forced with an idealized wind stress pattern based on the observed storm parameters in hurricane Frederic. In an analytical model, the Green's function (K0) is convolved with the wind stress curl to predict a sea surface depression of approximately 20 cm from the equilibrium position. The near-inertial velocities are simulated by convolving the slope of the sea surface depression with a second Green's function. The barotropic current velocities rotate ...

Regional Rainfall Frequency Analysis via Stochastic Storm Transposition

In a previous study, Foufoula-Georgiou investigated a stochastic storm transposition (SST) approach as a possible methodology of assessing the probability of exceedance of extreme precipitation depths over a catchment. The purpose of this paper is to report further methodological advances on the SST approach and present the results of a pilot implementation study in the Midwest. Under the assumptions of an elliptical storm shape and spread function of a given functional form, extreme storms have been described by the joint probability distribution of seven storm parameters (five specifying the magnitude, orientation, shape, and within-storm spatial variability, and two specifying the location of the storm center). A nonhomogeneous spatial multivariate point process model has been postulated for the joint probability distribution of the storm center depth and storm location and it has been fitted to 65 extreme storms in the nine-state midwestern region. The method has been used to estimate the tails of the probability distribution of the average catchment depths over several hypothetical catchments in the Midwest and to describe the spatial variability of the estimates over the studied region.

Radar observations of precipitation production in thunderstorms

Abstract Precipitation production is investigated for 9 intense thunderstorms that developed over the Lowveld in South Africa. A C‐band radar is used to observe the 3‐dimensional reflectivity pattern. Using an empirical relation between reflectivity factor and precipitation content and integrating over the storm volume provides an estimate of the total precipitation content aloft. Likewise, an area integration of the instantaneous rain rate at cloud base yields an estimate of the rate of total outflow. At their maturing stage, the storms had precipitation contents of 0.2 to 5.0 Tg and rainfall rates of about 0.3 to 2.0 Gg s−1. The total accumulation of rain at the ground ranged from 1 to 10 Tg. The characteristic storm updraft, defined as the ratio of the area‐averaged rainfall rate to the volume‐averaged precipitation content, was about 5 ms−1 for all storms. The time evolution of integral storm parameters is also presented and related to the overall storm development. The precipitation production values observed in the Lowveld storms compares well with previous estimates reported for large thunderstorms observed in Alberta and New England.

Hurricane‐generated currents on the outer continental shelf: 2. Model sensitivity studies

A numerical model described and verified in part 1 of this two‐part series (Cooper and Thompson, this issue) is applied to study the sensitivity of hurricane‐generated currents on the outer shelf and slope. Numerical experiments are performed in a simple basin with a straight shelf. The sensitivity of the response to changes in storm parameters, direction of storm approach, and topography is quantified. Response is measured in terms of the mixed‐layer velocity and depth at sites along the storm track. Results reveal the most important factors are (in decreasing order) wind speed, storm translation speed, direction of storm approach, asymmetry in the wind field, entrainment parameterization, and advection at slower storm translation speeds. Response is largely insensitive (less than 10%) to radius of maximum wind, shelf and slope configuration, bottom friction, atmospheric pressure gradients, and further reductions in the model grid size. For a storm approaching cross shelf, the response is primarily baroclinic (greater than 90%) and only weakly dependent (less than 10%) on the water depth at the site.