There is, I think, something ethereal about i —the square root of minus one. I remember first hearing about it at school. It seemed an odd beast at that time—an intruder hovering on the edge of reality.

Usually familiarity dulls this sense of the bizarre, but in the case of i it was the reverse: over the years the sense of its surreal nature intensified. It seemed that it was impossible to write mathematics that described the real world in …

I and i

Data Mining - Concepts and Techniques.

Abstract A two-dimensional version of the Pennsylvania State University mesoscale model has been applied to Winter Monsoon Experiment data in order to simulate the diurnally occurring convection observed over the South China Sea. The domain includes a representation of part of Borneo as well as the sea so that the model can simulate the initiation of convection. Also included in the model are parameterizations of mesoscale ice phase and moisture processes and longwave and shortwave radiation with a diurnal cycle. This allows use of the model to test the relative importance of various heating mechanisms to the stratiform cloud deck, which typically occupies several hundred kilometers of the domain. Frank and Cohen's cumulus parameterization scheme is employed to represent vital unresolved vertical transports in the convective area. The major conclusions are: Ice phase processes are important in determining the level of maximum large-scale heating and vertical motion because there is a strong anvil componen...

Numerical study of convection observed during the Winter Monsoon Experiment using a mesoscale two-dimensional model [presentation]

The purpose of this paper is to provide a comprehensive presentation and interpretation of the Ensemble Kalman Filter (EnKF) and its numerical implementation. The EnKF has a large user group, and numerous publications have discussed applications and theoretical aspects of it. This paper reviews the important results from these studies and also presents new ideas and alternative interpretations which further explain the success of the EnKF. In addition to providing the theoretical framework needed for using the EnKF, there is also a focus on the algorithmic formulation and optimal numerical implementation. A program listing is given for some of the key subroutines. The paper also touches upon specific issues such as the use of nonlinear measurements, in situ profiles of temperature and salinity, and data which are available with high frequency in time. An ensemble based optimal interpolation (EnOI) scheme is presented as a cost-effective approach which may serve as an alternative to the EnKF in some applications. A fairly extensive discussion is devoted to the use of time correlated model errors and the estimation of model bias.

The Ensemble Kalman Filter: Theoretical formulation and practical implementation

A new bulk microphysical parameterization (BMP) has been developed for use with the Weather Research and Forecasting (WRF) Model or other mesoscale models. As compared with earlier single-moment BMPs, the new scheme incorporates a large number of improvements to both physical processes and computer coding, and it employs many techniques found in far more sophisticated spectral/bin schemes using lookup tables. Unlike any other BMP, the assumed snow size distribution depends on both ice water content and temperature and is represented as a sum of exponential and gamma distributions. Furthermore, snow assumes a nonspherical shape with a bulk density that varies inversely with diameter as found in observations and in contrast to nearly all other BMPs that assume spherical snow with constant density. The new scheme’s snow category was readily modified to match previous research in sensitivity experiments designed to test the sphericity and distribution shape characteristics. From analysis of four idea...

/pdf/explicit-forecasts-of-winter-precipitation-using-an-improved-200vx38jzm.pdf

Explicit Forecasts of Winter Precipitation Using an Improved Bulk Microphysics Scheme. Part II: Implementation of a New Snow Parameterization

The design and development of a high-performance, dual-polarization, hybrid aperture-coupled microstrip patch antenna are presented. In the presented design, the horizontal and vertical polarizations are excited using the aperture coupling method. The isolation level of better than 51 dB and cross-polarization level of less than −30 dB are achieved from the measurement results of the designed single element. To achieve better cross-polarization levels, the $2 \times 2$ element subarrays of the proposed unit cell, while the horizontal polarization ports are mirrored, are designed and fabricated, and a lower than −39-dB cross-polarization level is achieved in the measurement results. Finally, to characterize the scan performance of the unit cell and subarray, a $4 \times 10$ element array of the proposed single element is fabricated and a better than −45-dB cross-polarization level is observed while scanning up to 45°.

/pdf/low-cross-polarization-high-isolation-microstrip-patch-1r5fm5yg3x.pdf

Low Cross-Polarization, High-Isolation Microstrip Patch Antenna Array for Multi-Mission Applications

Radar detection of a target embedded in geophysical media can be obscured by clutter. In this article the angular correlation function ( ) ACF is studied for wa! e scattering by an object embedded in random discrete scatterers under a rough surface. The ACF is calculated by using realization a! eraging, frequency a! eraging, and angular a! eraging. The results of the ACF for ! olume scattering, combined ! olume, and rough surface scattering and with a buried object are shown and compared. It is found that the ACF can be used to distinguish scattering by random discrete scatterers, random rough surface, and a deterministic buried object. The clutter return can be suppressed and the target becomes conspicuous. The ratio of ACF of the scattered wa! e with a target and that without a target can be 10 dB larger than the ratio of intensities. ! 1996 John Wiley & Sons, Inc. Microwave Opt Technol Lett 14, 144! 151, 1997.

The angular correlation function of wave scattering by a buried object embedded in random discrete scatterers under a random rough surface

In this paper, a system-specific phased-array radar system simulator was developed, based on a time-domain modeling and simulation method, mainly for system performance evaluation of the future Spectrum-Efficient National Surveillance Radar (SENSR). The goal of the simulation study was to establish a complete data quality prediction method based on specific radar hardware and electronics designs. The distributed weather targets were modeled using a covariance matrix-based method. The data quality analysis was conducted using Next-Generation Radar (NEXRAD) Level-II data as a basis, in which the impact of various pulse compression waveforms and channel electronic instability on weather radar data quality was evaluated. Two typical weather scenarios were employed to assess the simulator’s performance, including a tornado case and a convective precipitation case. Also, modeling of some demonstration systems was evaluated, including a generic weather radar, a planar polarimetric phased-array radar, and a cylindrical polarimetric phased-array radar. Corresponding error statistics were provided to help multifunction phased-array radar (MPAR) designers perform trade-off studies.

Phased-Array Radar System Simulator (PASIM): Development and Simulation Result Assessment

[1] Atmospheric imaging radars offer the capability to scrutinize structures within the illuminated volume at high temporal and spatial resolutions. The retrieval of the mean signal power using an imaging radar is obtained by subtracting the noise power from the covariance function at lag zero. The results obtained at low signal-to-noise ratio (SNR) are problematic when the noise power is unsuccessfully estimated, and are difficult to interpret when adaptive weights are used because of the temporally varying noise power. In this paper, a processing technique that improves the retrieval of the mean signal power by exploiting the temporal correlation difference between the desired signal and system noise is presented. Simulations of its performance are presented for the special case of a Gaussian received spectrum for variations in SNR, normalized spectrum width, and number of time series samples. The technique is also applied to real data collected with the Turbulent Eddy Profiler, a vertically pointing phased array radar developed at the University of Massachusetts, between 1435 and 1457 UTC 15 June 2003. Even though the performance of this technique in terms of its variance and bias depends on the SNR, spectrum width, and number of time series samples, results from both simulations and real data are promising as an enhanced mean signal power in the low SNR regions is obtained.

/pdf/reducing-the-effects-of-noise-on-atmospheric-imaging-radars-2it7nolgj8.pdf

Reducing the effects of noise on atmospheric imaging radars using multilag correlation

On 14 June 2011, thunderstorms developed along a cold front in central Oklahoma in a thermodynamic environment that was conducive for downbursts. One of the thunderstorms produced a wet downburst in Norman, Oklahoma, that resulted in surface winds in excess of 35 m s−1 (>80 mi h−1) and hailstones in excess of 4 cm in diameter. Unique 1-min observations of the downburst were recorded by an Oklahoma Mesonet station. These observations indicated a 6.6-hPa pressure rise that was coincident with a rain rate of 213 mm h−1 at the center of the downburst. In this event, both the research KOUN (Norman) and operational KTLX (Oklahoma City, Oklahoma) Weather Surveillance Radar-1988 Doppler (WSR-88D) instruments were scanning this downburst and its parent storm at close range (<30 km). KOUN provided polarimetric radar data (PRD) while both radars provided limited dual-Doppler coverage. The evolution of the downburst is analyzed mostly through the use of reconstructed range–height indicators of the PRD. A hydr...

Guifu Zhang

Papers

Low Cross-Polarization, High-Isolation Microstrip Patch Antenna Array for Multi-Mission Applications

The angular correlation function of wave scattering by a buried object embedded in random discrete scatterers under a random rough surface

Phased-Array Radar System Simulator (PASIM): Development and Simulation Result Assessment

Reducing the effects of noise on atmospheric imaging radars using multilag correlation

Characterization of the 14 June 2011 Norman, Oklahoma, Downburst through Dual-Polarization Radar Observations and Hydrometeor Classification