Dong-In Lee

Polarimetric Attenuation Correction in Heavy Rain at C Band

Abstract The ability of C-band polarimetric radar to account for strong attenuation/differential attenuation is demonstrated in two cases of heavy rain that occurred in the Chicago, Illinois, metropolitan area on 5 August 2008 and in central Oklahoma on 10 March 2009. The performance of the polarimetric attenuation correction scheme that separates relative contributions of “hot spots” (i.e., strong convective cells) and the rest of the storm to the path-integrated total and differential attenuation has been explored. It is shown that reliable attenuation correction is possible if the radar signal is attenuated by as much as 40 dB. Examination of the experimentally derived statistics of the ratios of specific attenuation Ah and differential attenuation ADP to specific differential phase KDP in hot spots is included in this study. It is shown that these ratios at C band are highly variable within the hot spots. Validation of the attenuation correction algorithm at C band has been performed through cross-che...

The Fluctuation of Aerosol Number Concentration by Wind Field Variation during Snowfall at the Southwestern Coastal Area

To understand the development mechanism of the aerosols in the surface boundary layer, the variation in the aerosol number concentration due to the divergence and convergence of the wind fields was investigated. The aerosol number concentration was measured in the size ranges of using a laser particle counter(LPC) from 0000 LST on 03 Feb. to 0600 LST on 07 Feb. 2004 at Mokpo in Korea during snowfall. The Velocity Azimuth Display(VAD) technique was used to retrieve the radar wind fields such as the horizontal wind field, divergence, and deformations including the vertical air velocity from a single Doppler radar. As a result, the distribution of the aerosol number concentration is apparently different for particles larger than during snowfall, and it has a tendency to increase at the beginning of the snowfall. The increase and decrease in the aerosol concentration due to the convergence and divergence of the wind fields corresponded to the particles with diameters greater than . It is found that the fluctuations in the aerosol number concentration are well correlated with the development and dissipation of snowfall radar echoes due to the convergence and divergence of horizontal wind fields near the surface boundary layer in the inland during the snowfall.

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.

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.

Estimates of Aerosol Indirect Effect from Terra MODIS over Republic of Korea

Moderate resolution imaging spectroradiometer (MODIS) data have been analyzed over four different regions (Yellow sea, Korean inland, East Sea, and South Sea) in Republic of Korea to investigate the seasonal variability of aerosol-cloud properties and aerosol indirect effect during the past decade (2000–2009). Aerosol optical depth (AOD) was found to be consistently high during spring. Cloud ice radius (CIR) also showed higher values during spring, while an enhancement in cloud water radius (CWR) and fine mode fraction (FMF) was observed during summer. AOD and aerosol index (AI) were found to be higher during January to June. However, FMF and CWR showed enhancement during July to December. Aerosol indirect effect (AIE) in each year has been estimated and found to be showing positive and negative indirect effects. The AIE for fixed cloud ice path (CIP) showed positive indirect effect (Twomey effect) over Yellow sea, while the AIE for fixed cloud water path (CWP) showed a major negative indirect effect (anti-Twomey effect) over all regions. During Changma (summer monsoon) period, the AIE for both CIP and CWP showed dominant anti-Twomey effect in middle and low level clouds, indicating the growth of cloud droplet radius with changes in aerosols, enhancing the precipitation.

The responses of cloudiness to the direct radiative effect of sulfate and carbonaceous aerosols

This study investigates the responses of the direct radiative effect of light absorbing and scattering carbonaceous and sulfate aerosols on cloudiness and associated radiative fluxes using an interactive aerosol-climate model coupled with a slab ocean model. We find that without including the impact of aerosols on cloud microphysics in the model (indirect effect), the direct radiative effect of aerosols alone can cause a change in cloud coverage and thus in cloud flux change which is consistent with several previous studies. More notably, our result indicates that the direct radiative effect of absorbing aerosols can cause changes in both low-level and high-level clouds with opposite signs. As a result, the global mean cloud radiation response to absorbing aerosols has a rather small value. The change of cloud solar radiative response (all-sky effect minus clear-sky effect) at the top of the atmosphere due to the existence of direct radiative effect of scattering, absorbing, and both types of aerosols is 0.72, 0.08, and 0.81Wm(-2), respectively, all are comparable in quantity to the current estimation of aerosol direct radiative forcing. The cloud response due to the longwave radiative effect is 0.09, 0.18, and 0.27Wm(-2), respectively. The global means of the radiative flux and cloud radiative responses appear to be linearly additive; however, this is definitely not the case for the zonal mean or at the regional scale. Key Points The effect of absorbing and scattering aerosols with an aerosol-climate model Cloud responses on the direct radiative are examined Nonlinearity from absorbing and scattering aerosols exists

Aerosol Modulation of Ultraviolet Radiation Dose over Four Metro Cities in India

This paper discusses the influence of aerosols on UV erythemal dose over four metro cities in India. Tropospheric Emission Monitoring Internet Service (TEMIS), archived UV-index (UV-I), and UV daily erythemal dose obtained from SCIAMACHY satellite were used in this study during June 2004 and May 2005 periods covering four important Indian seasons. UV-Index (UV-I), an important parameter representing UV risk, was found to be in the high to extreme range in Chennai (8.1 to 15.33), moderate to extreme range in Mumbai and Kolkata (5 to 16.5), and low to extreme over Delhi (3 to 15). Average UV erythemal dose showed seasonal variation from 5.9 to 6.3 KJm−2 during summer, 2.9 to 4.4 KJm−2 during postmonsoon, 3 to 4.5 KJm−2 during winter, and 5.1 to 6.19 KJm−2 during premonsoon seasons over the four cities. To estimate the influence of aerosols on reducing UV dose, UV aerosol radiative forcing and forcing efficiency were estimated over the sites. The average aerosol forcing efficiency was found to be from to  KJm−2 AOD−1 on different seasons. The study suggests that aerosols can reduce the incoming UV radiation dose by 30–60% during different seasons.

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.

Characterization of Aerosol Concentration during Severe Asian Dust Period at Busan, Korea in 20 March 2010

Asian dust (or yellow sand) occurring mainly in spring in East Asia is affected by the distribution of weather systems. This study was performed to investigate the characteristics of suspended particulate for Asian dust at Busan, Korea in 20 March 2010, which was one of the extreme case for the last 10 years. There was used the data of weather chart, satellite, automatic weather system (AWS), PM10, laser particle counter (LPC), and backward trajectories model. In synoptically, the high pressure was located in the northwestern part and low pressure was located in the northeastern part of Korea. The strong westerly winds from surface to upper layer makes it possible to move air masses rapidly. Air masses passing through Gobi Desert in Mongolia and Inner Mongolia plateau covered the entire Korean peninsula. As the results of aerosol analysis, PM10 concentration at Gudeok mountain in Busan was recorded 2,344 μg/m in 2300 LST 20 March 2010 and their concentration was markedly increased at coarse mode particle. In surface condition, westerly wind about 3 ∼ 5 m/s was dominant and small particles of 0.3 ∼ 0.5 μm were distributed on the whole. In heavy metal components analysis, the elements from the land was predominated.