Cheol-Hwan You

Rainfall Estimation Using Specific Differential Phase for the First Operational Polarimetric Radar in Korea

To assess the performance of rainfall estimation using specific differential phase observed by Bislsan radar, the first polarimetric radar in Korea, three rainfall cases occurring in 2011 were selected, each caused by different conditions: the first is the Changma front and typhoon, the second is only the Changma front, and the third is only a typhoon. For quantitative use of specific differential phase (), a data quality algorithm was developed for differential phase shift (), composed of two steps; the first involves removal of scattered noise and the second is unfolding of . This order of the algorithm is necessary so as not to remove unfolded areas, which are the real meteorological target. All noise was removed and the folded were unfolded successfully for this study. relations for S-band radar were calculated for 84,754 samples of observed drop size distribution (DSD) using different drop shape assumptions. The relation for the Bringi drop shape showed the best statistics: 0.28 for normalized error, and 6.7 mm for root mean square error for rainfall heavier than 10 mm . Because the drop shape assumption affects the accuracy of rainfall estimation differently for different rainfall types, such characteristics should be taken into account to estimate rainfall more accurately using polarimetric variables.

MULTIFRACTAL BEHAVIORS IN FOREIGN EXCHANGE MARKETS

A two-phase phenomenon in three financial exchange prices is studied. To understand the underlying mechanism for the formation of market prices, we perform the multifractal analysis and the detrended fluctuation analysis in terms of time series of market prices. We also examine higher order temporal correlations for the market price. Although the multifractal properties of market prices are obtained, it cannot be reproduced the binomial multiplicative process through that was used to understand fully developed turbulence.

Decadal Variation in Raindrop Size Distributions in Busan, Korea

This paper investigated the variability of raindrop size distributions (DSDs) in Busan, Korea, using data from two different disdrometers: a precipitation occurrence sensor system (POSS) and a particle size velocity (Parsivel) optical disdrometer. DSDs were simulated using a gamma model to assess the intercomparability of these two techniques. Annual rainfall amount was higher in 2012 than in 2002, as were the annually averaged (which was 0.1 mm greater in 2012) and the frequency of convective rain. Severe rainfall (greater than 20 mm h−1) occurred more frequently and with a larger in 2012. The values of from July, August, and December, 2012, were much greater than from other months when compared with 2002. Larger raindrops contributed to the higher rain rates that were observed in the morning during 2012, whereas relatively smaller raindrops dominated in the afternoon. These results suggest that the increase in raindrop size that has been observed in Busan may continue in the future; however, more research will be required if we are to fully understand this phenomenon. Rainfall variables are highly dependent on drop size and so should be recalculated using the newest DSDs to allow more accurate polarimetric radar rainfall estimation.

Algorithm Development for the Optimum Rainfall Estimation Using Polarimetric Variables in Korea

In this study, to get an optimum rainfall estimation using polarimetric variables observed from Bislsan radar which is the first polarimetric radar in Korea, rainfall cases for 84 hours caused by different conditions, which are Changma front and typhoon, Changma front only, and typhoon only, occurred in 2011, were analyzed. And rainfall algorithms were developed by using long period drop size distributions with six different raindrop axis ratio relations. The combination of the relations between and , , and , , and and with different rainfall intensity would be an optimum rainfall algorithm if the reference of rainfall would be defined correctly. In the case the reference is not defined adequately, the relation between and , , , and and , , can be used as a representative rainfall relation. Particularly if the qualified is not available, the relation between and , , can be used as an optimum rainfall relation in Korea.

Dual-Doppler radar analysis of a near-shore line-shaped convective system on 27 July 2011, Korea: a case study

In the summer rainy season, the Korean Peninsula is frequently influenced by severe weather phenomena such as floods and rain-induced landslides. A band-shaped precipitation system associated with unstable atmospheric conditions occurred over northwest Korea on 27 July 2011. This precipitation system produced heavy rainfall over the Seoul metropolitan area, which received over 80 mm h−1 of rainfall and suffered 70 weather-related fatalities. To investigate the precipitation system, we used diverse meteorological data of environmental condition and estimated three-dimensional wind field from dual-Doppler radar measurements of vertical air motion. Environmental conditions included high equivalent potential temperature (θ e ) of over 355 K at low levels, and low θ e of under 330 K at middle levels, causing vertical instability. Furthermore, a pressure trough was located to the northwest of Korea, favouring the development of the band-shaped precipitation system. The tip of the band-shaped precipitation system was made up of line-shaped convective systems (LSCSs) that caused flooding and landslides, and the LSCSs were continuously enhanced by merging between new cells and the pre-existing cell. The position of merging moved from the coast to offshore areas and influenced the positioning of the regions of enhanced convection. In turn, this affected the roughness of the convective cell and the internal structure of the enhanced convective regions. Onshore, the convective area was higher than in offshore areas because of strong convergence (≤−4×10−4 s−1) at low levels caused by friction over land. The strong convergence generated strong updraft (≥4 m s−1) that influenced the height of the convective area. The convective region offshore was wider than that onshore because of weak convergence (≥−2.2×10−4 s−1) at low levels. Updraft in offshore areas was weak (≤3 m s−1) compared with onshore, resulting in a lower and wider convective area. Spatial variations in surface roughness result in different structural features and profiles of divergence within LSCSs, even if they originate in the same convective region.

Neuro-Fuzzy Gust Front Detection Algorithm With S-Band Polarimetric Radar

A gust front (GF) is the leading edge of the cold outflow from a thunderstorm. The upgrade of the S-band Weather Surveillance Radar-1988 Doppler (WSR-88D) to dual-polarization has been completed recently in the U.S. Therefore, it is timely to exploit the added benefits of polarimetric variables to identify GFs. In this paper, six signatures derived from polarimetric WSR-88D data are developed to characterize GFs, including medium reflectivity, apparent thin line feature in reflectivity, and the motion of reflectivity quantified by a line feature parameter, high differential reflectivity, low copolar cross-correlation coefficient, apparent convergence manifested by the large radial shear, and large standard deviation of differential phase. These signatures are fuzzy in nature, and therefore, a novel neuro-fuzzy GF detection algorithm (NFGDA) is developed using a fuzzy logic inference system, which is optimized by a training process using a neural network. WSR-88D data from 11 cases (totaling 121 volume scans) are used to evaluate the performance of NFGDA and compared to the operational machine intelligent GF algorithm (MIGFA) with single polarization data. The results show that NFGDA can provide improved performance with a higher probability of detection of 92% (versus 78% with MIGFA), lower false alarm ratio of 0% (versus 9%), and higher percentage correct of 93% (versus 74%). Additional length-based scoring schemes show that NFGDA can correctly detect 62% (41% with MIGFA) of the total length of GFs, and minimize falsely detected length to 7% (61%).