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

Angular and range interferometry to measure wind (DOI 10.1029/2003RS002927)

The National Weather Radar Testbed (NWRT) system is based on WSR-88D technology enhanced with the significant capability of a Phased Array Antenna. The agile beam capability provides a unique and powerful tool to focus weather radar asset on observation of severe weather phenomena including structures that lead to formation of these storms. The NWRT system has demonstrated the ability to provide weather data consistent with that from adjacent WSR systems at greatly reduced volume coverage time. Significant success has been reported in use of this tool for gathering and presenting specific, real-time storm-cell 3-D data to weather scientists and meteorologists for in-depth interpretation of these pencil-beam radar returns. Specific extensions to the conventional weather radar capabilities now in place include Beam Multiplexing (spatial filtering), Oversampling and Whitening (signal processing) and Transverse Wind Estimation (multi-beam). The latter capability has recently been added by activating the difference beam channels of the array and sequentially sampling and comparing these with the conventional sum-only mode. Under the auspices of a National Science Foundation, Major Research Instrument (NSF/MRI) grant, and in cooperation with the United States Navy, the NWRT is now being extended with an 8-channel digital receiver for simultaneous processing of sum, difference and ancillary beam returns. Expectations are high that application of multi-beam adaptation algorithms and other signal processing techniques using multiple channels will lead to improved detection and storm queuing techniques to greatly extend the forecast lead time for severe storms. Multi-channel capability also opens the NWRT for the possibility of testing Multi-Function radar system algorithms and operations. This paper will describe the attributes of the COTS, rf-system extensions and the specific steps being taken to baseline these changes to the current NWRT system performance.

Multi-channel conversion of the National Weather Radar Testbed receiver

In this Letter, a dual-polarised aperture-coupled microstrip patch antenna with low cross-polarisation and high isolation is presented. A microstrip patch antenna is designed and fabricated to meet the multifunction phased array radar requirements. The proposed single element is fabricated and the measurement results along with simulation results have been presented, showing the performance of the designed single element. An input isolation of better than 50 dB and a cross-polarisation level of <;-30 dB are achieved in the measurements.

Dual-polarised hybrid feed microstrip patch antenna for multifunction application

The detection of an object buried under a random rough surface has important applications. The bistatic scattering intensity of the rough surface can be comparable to that of the object making it difficult to detect the buried object. The authors study the angular correlation functions (ACF) of scattering. They first study ACF of rough surface scattering. It is shown that a memory line is still exhibited for a single random rough surface of moderate extent based on frequency average. If the incident and scattered angles are away from the memory line of rough surface scattering, then the ACF of rough surface scattering is small. For the problem of buried object under a rough surface, numerical simulations indicate that even when the ratio of scattered intensities with and without the buried object is close to unity, the corresponding ratio of ACF can be 15 dB. Thus, using ACF is superior to using intensities in the detection of buried object.

Numerical study of detection of a buried object under a single random rough surface with angular correlation function

The authors described a three-layer mixed model to characterize microwave radiation from mixed phase cloud. The brightness temperature is calculated by numerically solving RT equation. The results are compared with that using the two-layer single-phase model and the difference in brightness temperature is up to 10 degree. The mixed phase RT model results are used to retrieve atmospheric parameters such as water vapor, liquid water path, ice water path and, mean ice droplet size. The results are encouraging, the technique will be applied for actual measurements, and radar data will be used for independent verification of the same.

Guifu Zhang

Papers

Angular and range interferometry to measure wind (DOI 10.1029/2003RS002927)

Multi-channel conversion of the National Weather Radar Testbed receiver

Dual-polarised hybrid feed microstrip patch antenna for multifunction application

Numerical study of detection of a buried object under a single random rough surface with angular correlation function

Microwave radiation from mixed phase cloud and parameter retrievals