Hi Ku Cho

HISTORICAL RECORDS OF ASIAN DUST EVENTS (HWANGSA) IN KOREA

The observation of dust events in Korea must have been important through its long history because of its geographical and meteorological setting. Descriptions about dust events were well documented in historical archives, such as Samguk sagi (57 BC–AD 938), Goryeo sa (918–1392), Joseon wangjosillok (1392–1853), and Munhuenbigo (~1776). In this study, records of Asian dust events were compiled from the above historical archives, covering the period of the second to the eighteenth century. These historical records were investigated along with the recent data (1915–2005) of dust event days in Seoul, Korea. The first record was made in AD 174 in Silla during the period of the Three Kingdoms. A dust event, now called hwangsa, was commonly written down as Woo-Tou or Tou-Woo standing for “dustfall” in the historical archives. Asian dust events took place most frequently during spring from March to May and there was almost no occurrence in summer. The main seasonal feature of the historical dust events was found ...

Effects of ozone and aerosol on surface UV radiation variability.

Global (direct+diffuse) spectral ultraviolet (UV, 290-363nm) and total ozone measurements made on the roof of the Main Science Building, Yonsei University at Seoul (37.57°, 128.98°E) were analyzed to quantify the effects of ozone and aerosol on the variability of surface erythemal UV (EUV) irradiance. The measurements have been made with a Brewer Spectrophotometer MKIV (SCI-TEC#148) and a Dobson Ozone Spectrophotometer (Beck#123), respectively, during 2004-2008. The overall mean radiation amplification factor, RAF(AOD, SZA) [23,24] due to total ozone (O(3)) (hereafter O(3) RAF) shows that 1% decrease in total ozone results in an increase of 1.18±0.02% in the EUV irradiance with the range of 0.67-1.74% depending on solar zenith angles (SZAs) (40-70°) and on aerosol optical depths (AODs) (<4.0), under both clear (cloud cover<25%) and all sky conditions. For the mean AOD, the O(3) RAFs(SZA) for both sky conditions increased as SZA increased from 40° to 60°, and then decreased for higher SZA 70°, where the patterns are consistent with results of the previous studies [2,10]. A similar analysis of the RAF(O(3), SZA) due to AOD (hereafter AOD RAF) under clear and all-sky conditions shows that on average, a 1% increase in AOD forces a decrease of 0.29±0.06% in the EUV irradiance with the maximum range 0.18-0.63% depending on SZAs and O(3). Thus, overall sensitivity of UV to ozone (O(3), RAF) was estimated to be about four times higher than to the aerosol (AOD RAF). At the mean O(3), the AOD RAFs(SZA) for both skies appears to be almost independent of SZAs. It is shown that the O(3) RAFs are nearly independent of the sky conditions, whereas the AOD RAFs depend distinctly on the sky conditions with the larger values for all skies. Under cloud free conditions, the overall mean ratio for measured-to-modeled O(3), RAF(AOD, SZA) is 1.13, whereas the ratio for AOD RAF(O(3), SZA) shows 0.82 in the EUV irradiance. Overall, the RAF measurements are corroborated by radiative transfer model calculations under clear-sky conditions.

Recent Changes in Downward Longwave Radiation at King Sejong Station, Antarctica

Abstract Effects of cloud, air temperature, and specific humidity on downward longwave irradiance and their long-term variabilities are examined by analyzing the measurements made at the King Sejong Station in the Antarctic Peninsula during the period of 1996–2006. It has been shown that the downward longwave irradiance (DLR) is significantly correlated with three variables: air temperature, specific humidity, and cloudiness. Based on the relationship of the three variables with DLR, a multiple linear regression model has been developed in order to evaluate the relative contribution of each of the variables to the variation of DLR. The three variables together explained 75% of all the variance in daily mean DLR. The respective contribution from specific humidity and cloudiness to the variation of DLR was 46% and 23%; thus most of the DLR variability can be explained by the variations in the two variables. The annual mean of longwave cloud forcing shows 52 W m−2 with no remarkable seasonal cycle. It is als...

The dependence of the surface solar irradiance on cloud and aerosol

To quantify radiative forcing of aerosol and to investigate the dependence of the horizontal UV, visible and NIR on total optical depth (TOD) and cloudiness, narrowband surface solar irradiances were measured and analyzed for direct and diffuse component. A MFRSR (Multifilter Rotating Shadowband Ratiometer) was used to measure the global, direct and diffuse solar irradiances atone broadband of 391–955 nm and 6 narrowband channels of 412.8, 495.2, 611.9, 672.2, 869, 936.6 nm for a year from Jan. to Dec. in 2006 at Yonsei University in Seoul and a UV‐MFRSR was used to measure irradiance at 7 narrowband channels of 299.1, 304.5, 310.7, 317.1, 323.8, 331.3, 367.4 nm in UV range during 7 months at the same location with the MFRSR.

Aerosol and CO loading in the atmosphere observed by the MODIS and MOPITT: Russian forest fire case

The Moderate-resolution Imaging Spectroradiometer (MODIS) provides aerosol optical depth (AOD) along with the fine mode fraction over ocean and darker land surfaces. Measurement Of Pollution In The Troposphere (MOPITT) onboard the Terra satellite provides quantitative information of carbon monoxide (CO). Measurements of CO whose principal sources arise from anthropogenic emissions such as biomass burning and forest fires, is very useful for tracing fire emissions in the atmosphere. In this study, intense fires in the southeast part of Russia in May, 2003 are studied with the satellite data from MODIS and MOPITT. The AOD distribution from the MODIS for May, 2003 show stretched regions of high AODs near the Korean Peninsula. The CO concentrations at 700 hPa from the MOPITT for May, 2003 also show enhanced values. Correlation between CO and AOD are investigated for the forest fire case. This multi-instrumental approach to monitor the aerosol in the atmosphere is expected to contribute to the classification of the aerosol characteristics in the atmosphere, carbonaceous aerosol in particular.

Vertical O3 profiling and error analysis by UV radiometer onboard KSR-III

Ozone density profile over the Korean peninsula was obtained by UV radiometer onboard the KSR-III (Korea Sounding Rocket-III) launched in Nov. 2002 and compared with other observations from satellites and ozonesonde. Due to altitude limitations in this first test flight of the newly-developed system, the apogee of the rocket was still in the stratosphere. Most of the previous algorithm for the optical absorption technique assumed to have measurements out of the ozone layer but our situation provided an opportunity to consider an algorithm to retrieve the vertical profiles of O3 number density for the rocket flight whose apogee is still in the ozone layer. In measurements by using optical instruments, various error sources exist in characterizing optical properties of detectors and atmospheric parameters. The magnitude of errors are analyzed and estimated in various rocket soundings but their quantitative effects of error sources due to each parameter in the retrieval have not been investigated in detail yet. In this paper, the quantitative error effects on the retrieval algorithm are investigated with respect to the altitudes. It is worthwhile to investigate this error sources for the current sounding as well as to reevaluate the previous rocket sounding data. Among retrieval parameters, the most influential error sources are found to be the absorption cross section and the filter response function. +0.65 nm shift in filter response function or -0.55 nm shift errors in absorption cross section are found to result in 5% deviation on the total number density. Whereas the total number density profiles are not so sensitive to the Rayleigh scattering or the slant air column density assumed. The stray light effect of the interference filter was also investigated.

UV Sensitivity to Changes in Ozone, Aerosols, and Clouds in Seoul, South Korea

AbstractThe total ozone (O3) and aerosol optical depth (AOD) at 320 nm have been observed from the ultraviolet (UV) measurements made at Yonsei University in Seoul, South Korea, with Dobson and Brewer spectrophotometers, respectively, during 2004–10. The daily datasets are analyzed to show the sensitivities of UV radiation to changes in O3, AOD, and cloud cover (CC) together with global solar radiation (GS), including the long-term characteristics of surface UV irradiance in Seoul. The UV sensitivities show that 1% increases of O3 and AOD relative to their reference values under all- and clear-sky conditions similarly manifest as 1–1.2% and 0.2% decreases of both daily erythemal UV (EUV) and total UV (TUV) irradiance at the ground level except for TUV sensitivity to O3 (~0.3%). Those UV sensitivities to CC and GS changes are associated with a 0.12% decrease and 0.7% increase, respectively, in fractional UV changes. The trends show that the positive trends of O3 (+7.2% decade−1), AOD (+22.4% decade−1), and...

Wavelength Dependency of Aerosol Optical Properties in Seoul

In this study, wavelength dependency of aerosol was investigated using the correlation between Single scattering albedo (SSA) and Angstrom exponent (AE), the time series of SSA difference in accordance with wavelength, and the relationship between SSA and AE ratio which defined AE at longer wavelength pair over AE at shorter wavelength pair. All used data in this study are daily mean values. The positive correlation between SSA and AE becomes clear as the wavelength pair of AE becomes longer, however negative correlation with AE at shorter wavelength pair also cannot be neglected. Accordingly, the correlation is well negative between SSA at longer wavelength (LW‐SSA) and AE at shorter wavelength pair (SW‐AE), opposite to the well positive correlation between SSA at shorter wavelength (SW‐SSA) and AE at longer wavelength pair (LW‐AE). SSA also shows the interesting relationship with AE ratio. In this study, AE ratio is defined as AE at 675–1020 nm over AE at 340–675 nm. Their relation shows the quadratic c...