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...

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

An infinitesimal dipole model (IDM) for an antenna including mutual coupling is used to model the radiation patterns of aperiodic arrays. Each radiating element is modelled by a set of infinitesimal dipoles. The mutual coupling between the elements is calculated and the far field radiation pattern of the antenna is computed in a fast and efficient manner. An invasive weed optimisation algorithm is employed to find both the IDMs and the aperiodic array. The simulation results using IDM are verified with a full-wave analysis.

Modelling of aperiodic array antennas using infinitesimal dipoles

The key goal in designing a dual polarisation antenna array is to achieve a low cross-polarisation level. The cross-polarisation suppression method in dual linear polarisation phased array antenna is illustrated by using a dual linear penalisation probe-fed patch element. The array consists of a number of identical 2 × 2 element sub-arrays in which the H-port and V-port locations on each element are changed. A 2 × 2 element sub-array has been fabricated and the measurements and simulation results are provided to show the accuracy of this cross-polarisation suppression method. In addition, the co- and cross-polarisation patterns of the cylindrical array are presented.

Cross-polarisation suppression in cylindrical array antenna

A novel planar array antenna configuration for cross-polarization suppression is presented. Array configuration has a significant effect on the total array cross-polarization ratio, which is studied here. A simple dual-linear probe-fed stacked microstrip antenna is designed and used to implement this new planar array antenna configuration. Simulation results show that the cross-polarization ratio level is significantly improved at broadside and off-broadside steering angles.

Dual-linear polarization phased array antenna cross-polarization suppression using a novel image configuration

The design, modeling and measurement results of a mid-size cylindrical polarimetric phased array radar (CPPAR) antenna for weather sensing applications is presented. The beam scanning in the elevation is obtained using the frequency scanning concept while the azimuth scanning is achieved using both the commutation and the beam scanning. The maximum elevation scan angle is about 20 degrees and the frequency range is from 2.7 to 3.0 GHz. The cylindrical array consists of 96 frequency scanning vertical columns mounted on the surface of cylinder with the diameter and height of 2 meters. Each antenna column consists of 19 stacked microstrip patch elements fed by two series feed striplines terminated to matched loads. The patch elements are excited through the aperture on the ground plane. The antenna column is modeled using a full wave solution and then it is fabricated and tested in an anechoic chamber. In addition, the simulation results of the full cylinder consisting of 96 antenna columns are presented.

Cylindrical polarimetric phased array radar demonstrator: Design and analysis of a frequency scanning antenna array

Drop size distribution (DSD) is a fundamental parameter in rain microphysics. Retrieving DSDs from polarimetric radar measurements extends the capabilities of rain microphysics research and...

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Guifu Zhang

Papers

Modelling of aperiodic array antennas using infinitesimal dipoles

Cross-polarisation suppression in cylindrical array antenna

Dual-linear polarization phased array antenna cross-polarization suppression using a novel image configuration

Cylindrical polarimetric phased array radar demonstrator: Design and analysis of a frequency scanning antenna array

Uncertainty in Retrieving Raindrop Size Distribution from Polarimetric Radar Measurements