Kyung-Eak Kim

Identification and Removal of Ground Echoes and Anomalous Propagation Using the Characteristics of Radar Echoes

Abstract This paper explores the removal of normal ground echoes (GREs) and anomalous propagation (AP) in ground-based radars using a fuzzy logic approach. Membership functions and their weights are derived from the characteristics of radar echoes as a function of radar reflectivity. The dependence on echo intensity is shown to significantly improve the proper identification of GRE/AP. In addition, the proposed method has a better performance at lower elevation angles. The overall performance is comparable with that from a polarimetric approach and can thus be easily implemented in operational radars.

A Preliminary Analysis of Spatial Variability of Raindrop Size Distributions during Stratiform Rain Events

Abstract The spatial variability of raindrop size distributions (DSDs) and precipitation fields is investigated utilizing disdrometric measurements from the four Precipitation Occurrence Sensor Systems (POSS) and radar reflectivity fields from S-band dual-polarization radar and vertically pointing X-band radar. The spatial cross correlation of the moments of DSDs, their ratio, error in rainfall estimate, and normalization parameters are quantified using a “noncentered” correlation function. The time-averaged spatial autocorrelation function of observed radar reflectivity factor (Ze) is smaller than that of estimated rainfall rate from Ze because of power-law R–Z transformation with its exponent larger than unity. The important spatial variability of DSDs and rain integral fields is revealed by the significant differences among average DSDs and leads to an average fractional error of 25% in estimating rainfall accumulation during an event. The spatial correlation of the reflectivity from POSS is larger tha...

Use of the Doppler Spectral Width to Improve the Estimation of the Convective Boundary Layer Height from UHF Wind Profiler Observations

Abstract Enhancement of the air refractive index structure parameter C2n often occurs at the top of the convective boundary layer (CBL), where the absolute values of the vertical gradients of virtual potential temperature and mixing ratio have a peak. This well-known behavior of the C2n profiles is often used to locate the height of the mixed layer Zi from UHF wind profiler observations. In the present study, Zi determination with the C2n-based technique was investigated for a case of clear-air CBL and a case of cloud-topped CBL. In certain circumstances, such as multifold C2n peaks or poorly defined peaks, these techniques fail to correctly retrieve CBL height. In order to improve Zi determination, a new method based on the conjoint use of C2n and Doppler spectral width profiles is proposed and discussed.

Evaluation of Boundary Layer Similarity Theory for Stable Conditions in CASES-99

Abstract The Monin–Obukhov similarity theory and a generalized formulation of the mixing length for the stable boundary layer are evaluated using the Cooperative Atmosphere–Surface Exchange Study-1999 (CASES-99) data. The large-scale wind forcing is classified into weak, intermediate, and strong winds. Although the stability parameter, z/L, is inversely dependent on the mean wind speed, the speed of the large-scale flow includes independent influences on the flux–gradient relationship. The dimensionless mean wind shear is found to obey existing stability functions when z/L is less than unity, particularly for the strong and intermediate wind classes. For weak mean winds and/or strong stability (z/L > 1), this similarity theory breaks down. Deviations from similarity theory are examined in terms of intermittency. A case study of a weak-wind night indicates important modulation of the turbulence flux by mesoscale motions of unknown origin.

Experimental determination of proton-induced cross-sections on natural zirconium

We measured cross-sections for the formation of (86g,87m,87g)Y, (88,89g)Zr, and (90,92m)Nb radionuclides for proton-induced reactions on natural zirconium by using a conventional stacked-foil activation technique in the energy range between 1 and 40MeV at the MC-50 cyclotron of the Korea Institute of Radiological and Medical Science. We compared the measured data with the available literature data and the theoretical calculation by the model codes TALYS and ALICE-IPPE. We also deduced the integral yields for thick targets from the measured cross-sections of the produced radionuclides. The optimum production possibility of the medically important (89g)Zr and (86)Y radionuclides were discussed elaborately.

Persistent organic pollutants in adipose tissue should be considered in obesity research

Although low doses of persistent organic pollutants (POPs), strong lipophilic chemicals with long half‐lives, have been linked to various endocrine, immune, nervous and reproductive system diseases, few obesity studies have considered adipose tissue as an important POPs exposure source. Because the toxicodynamics of POPs relate directly to the dynamics of adiposity, POPs might explain puzzling findings in obesity research. In two people exposed to the same amounts of environmental POPs, the one having more adipose tissue may be advantaged because POPs storage in adipose tissue can reduce burden on other critical organs. Therefore, adipose tissue can play a protective role against the POPs effects. However, two situations increase the POPs release from adipose tissue into the circulation, thereby increasing the risk that they will reach critical organs: (i) weight loss and (ii) insulin resistance. In contrast, weight gain reduces this possibility. Therefore, avoiding harmful health effects of POPs may mostly contradict conventional judgments about obesity and weight change. These contradictory situations can explain the obesity paradox, the adverse effects of intensive intentional weight loss and the protective effects of obesity against dementia. Future studies should consider that adipose tissue is widely contaminated with POPs in modern society.

Investigations of the natTi(p,x)43,44m,44g,46,47,48Sc,48V nuclear processes up to 40 MeV

Independent and cumulative production cross-sections for the (nat)Ti(p,x)(48)V, (43,44m,44g,46,47,48)Sc nuclear processes are reported here, for the energy region of 4-38MeV by using a stacked-foil activation technique. Measured data were critically compared with the earlier reported values, and also with the theoretical data from the TALYS and ALICE-IPPE codes. The measured (nat)Ti(p,x)(48)V reaction is important for charged particle beam monitoring purposes, whereas the (43,44,47)Sc radionuclide have various practical applications in nuclear medicine.

Quality Control and Tilt Correction Effects on the Turbulent Fluxes Observed at an Ocean Platform

This study investigates atmospheric factors influencing the quality and the postprocessing (e.g., tilt correction) of fast-response measurements of turbulent fluxes for difficult open-sea measurements over an offshore platform. The data were collected at the Ieodo Ocean Research Station over the Yellow Sea during the periodfrom 5 November 2007 to19 February2008.The qualitycontrol removalof the data generallydepends on wind speed, relative humidity, significant wave height, visibility, and stability. The removal of substantial water vapor data with weak-wind stable conditions is investigated. Three different tilt correction algorithms (double rotation, triple rotation, and planar fit) are applied to correct the data because of inadvertent tilt of sonic anemometers. The choice of tilt correction method significantly influences the angle between the wind and stress direction.

An analysis of Characteristics of Heavy Rainfall Events over Yeongdong Region Associated with Tropopause Folding

The synoptic and kinematic characteristics of a heavy rainfall that occurred in Gangneung region on 22 to 24 October 2006 were investigated using weather maps, infrared images, AWS observation data and NCEP global final analyses data. The total amount of rainfall observed in the region for the period was 316.5 mm, and the instanteneous maximum wind speed was . According to the analysis of weather maps, before the starting of the heavy rainfall, an extratropical low pressure system was developed in the middle region of the Korean Peninsula, and an inverted trough was formed in the northern region of the peninsula. In addition, a jet stream on the upper charts of 300 hPa was located over the Yellow Sea and the southern boundary of the peninsula. A cutoff low in the cyclonic shear side of the upper jet streak, which was linked to an anomaly of isentropic potential vorticity, was developed over the northwestern part of the peninsula. And there are analyzed potential vorticity and wind, time-height cross section of potential vorticity, vertical air motion, maximums of the divergence and convergence and vertical distribution of potential temperature in Gangneung region. The analyzed results of the synoptic conditions and kinematic processes strongly suggest that the tropopause folding made a significant role of initializing the heavy rainfall.

A Case Study of Mesoscale Convective Band (MCB) Development and Evolution along a Quasi-stationary Front

This paper presents a case study of mesoscale convective band (MCB) development along a quasi-stationary front over the Seoul metropolitan area. The MCB, which initiated on 1500 UTC 20 September 2010 and ended on 1400 UTC 21 September 2010, produced a total precipitation amount of 259.5 mm. The MCB development occurred during a period of tropopause folding in the upper level and moisture advection with a low-level jet. The analyses show that the evolution of the MCB can be classified into five periods: (1) the cell-forming period, when convection initiated; (2) the frontogenetic period, when the stationary front formed over the Korean peninsula; (3) the quasi-stationary period, when the convective band remained over Seoul for 3 h; (4) the mature period, when the cloud cover was largest and the precipitation rate was greater than 90 mm h−1; and (5) the dissipating period, when the MCB diminished and disappeared. The synoptic, thermodynamic, and dynamic analyses show that the MCB maintained its longevity by a tilted updraft, which headed towards a positive PV anomaly. Precipitation was concentrated under this area, where a tilted ascending southwesterly converged with a tilted ascending northeasterly, at the axis of cyclonic rotation. The formation of the convective cell was attributed in part by tropopause folding, which enhanced the cyclonic vorticity at the surface, and by the low-level convergence of warm moist air and upperlevel divergence. The southwesterly flow ascended in a region with high moisture content and strong relative vorticity that maintained the development of an MCB along the quasi-stationary front.