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국제학술지

공지 (2024. 9. 4.)

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Sensitivity of satellite-derived wind retrieval over cloudy scenes to target selection in tracking and pixel selection..

Abstract: Satellite-derived atmospheric motion vectors (AMVs) are useful in weather analyses such as for identifying tropical lows, wind shears, and jet locations. AMVs are assimilated into numerical weather prediction models, particularly for ocean areas where wind observations are sparse. An AMV's accuracy is closely related to the processes of target tracking and height assignment (HA). The objective of this paper is to investigate the sensitivity of satellite-derived wind retrieval in cloudy scenes to the main components in these processes. AMVs are retrieved by identifying and tracking targets using advanced pattern-matching techniques based on cross-correlation statistics. In tracking targets, the main components of the AMV algorithm are the target selection methods such as the target box size, the grid size, the time interval between satellite images, and the method for determining the locations of targets. This study reveals that the optimal sizes of the target and grid could be determined differently according to the channel used for wind observation. The time interval between satellite images has a significant impact on the number of vectors with high quality and high accuracy. The HA method is also an important factor in determining the AMVs' accuracy. The heights of most vectors are assigned to cloud-top pressures using the representative radiances, and the current algorithm uses the coldest pixels to set these representative radiances. The template image used for feature tracking may contain various clouds with different movements and different heights. Therefore, without any information on feature tracking, the current approach may lead to HA errors. To mitigate these HA errors, a new approach using the individual-pixel contribution rate is tested. It tends to correct the heights of the AMVs using the water vapor channel and reduces the wind speed bias and root-mean-square vector difference. Full title: Sensitivity of satellite-derived wind retrieval over cloudy scenes to target selection in tracking and pixel selection in height assignment
- 작성자Park et al.
- 작성일2024.08.30
- 조회수14
- 2012
The observed variation in cloud-induced longwave radiation in response to SST over the Pacific warm pool from MTSAT-1R..

Abstract: This study investigated variations in outgoing longwave radiation (OLR) in response to changes in sea surface temperature (SST) over the Pacific warm pool area (20°N–20°S, 130°E–170°W). OLR values were obtained from recent (January 2008–June 2010) geostationary window channel imagery at hourly resolution, which resolves processes associated with tropical convective clouds. We used linear regression analysis with the domain-averaged OLR and SST anomalies (i.e., ΔOLR, ΔSST; deviations from their 90-day moving averages). Results show that the regression slope appears to be significant only with SST least-affected by cloud radiative forcing, for which SST needs to be obtained as daily average over cloud-free regions (ΔSSTclear). The estimated value of ΔOLR/ΔSSTclear is 15.72 W m−2 K−1, indicating the presence of strong outgoing longwave radiation in response to surface warming. This atmospheric cooling effect is found to be primarily associated with reduced areal coverage of clouds (−14.4% K−1).
- 작성자Cho et al.
- 작성일2024.08.30
- 조회수11
- 2012
The potential of vegetation feedback to alleviate climate aridity over the U. S. associated with a 2×CO2 climate...

Abstract: This study examines the potential impact of vegetation feedback on changes in summer climate aridity over the contiguous United States (US) due to the doubling of atmospheric CO2 concentration using a set of 100-year-long climate simulations made by a global climate model interactively coupled with a dynamic vegetation model. The Thornthwaite moisture index (Im), which quantifies climate aridity on the basis of atmospheric water supply (i.e., precipitation) and atmospheric water demand (i.e., potential evapotranspiration, PET), is used to measure climate aridity. Warmer atmosphere and drier surface resulting from increased CO2 concentration increase climate aridity over most of the contiguous US. This phenomenon is due to larger increments in PET than in precipitation, regardless of the presence or absence of vegetation feedback. Compared to simulations without active dynamic vegetation feedback, the presence of vegetation feedback significantly alleviates the increase in aridity. This vegetation-feedback effect is most noticeable in the subhumid regions such as southern, midwestern and northwestern US, primarily by the increasing vegetation greenness. In these regions, the greening in response to warmer temperatures enhances moisture transfer from soil to atmosphere by evapotranspiration (ET). The increased ET and subsequent moistening over land areas result in weaker surface warming (1–2 K) and PET (3–10 mm month−1), and greater precipitation (4–10 mm month−1). Collectively, they result in moderate increases in Im. Our results suggest that moistening by enhanced vegetation feedback may prevent aridification under climatic warming especially in areas vulnerable to climate change, with consequent implications for mitigation strategies. Full title: The potential of vegetation feedback to alleviate climate aridity over the United States associated with a 2×CO2 climate condition
- 작성자Park et al.
- 작성일2024.08.30
- 조회수14
- 2012
Tropical cyclone contribution to the interdecadal change in summer rainfall over South China in the early 1990s

This study investigated the tropical cyclone (TC) rainfall (PTC) contribution to the interdecadal change in summer (June, July and August) rainfall (PTotal) over South China between 1981-1992 (ID1) and 1993-2002 (ID2). In an area-averaged sense, the interdecadal change in PTotal was largely attributed to non-TC rainfall for the summer total and months of June and July, while PTC became comparable in August. When the month-to-month spatial variability was considered, noticeable negative PTC contributions showed up over the southeastern coast, Hainan Island, and Taiwan in June and over the southern coastal regions in July. In contrast, a positive PTC contribution spread over South China with its maxima over the southern coastal regions in August, a pattern which appeared to be diametrically opposed to that of the negative PTC contribution in July, though the latter was less significant. The negative PTC contribution over the coastal and insular regions in June and July corresponded to less TC activity there. In June, it was attributed to reduced basin-wide TC activity due to prevailing unfavorable large-scale environments in ID2, whereas, in July, to less TC approaches from the Philippine Sea due to an enhanced cyclonic circulation centered on Taiwan in ID2. Conversely, in August, the overall enhanced positive PTC contribution was mainly by the direct influences of increased TC formations over the South China Sea in ID2.
- 작성자Kim et al.
- 작성일2024.08.30
- 조회수14
- 2012
The influences of interannual stratification variability and wind stress forcing on ENSO before and after the 1976...

Abstract: In order to understand the change in oceanic variability associated with the climate shift of the mid-1970s, we analyze the contribution of momentum forcing to the leading baroclinic modes over the tropical Pacific using Simple Ocean Data Assimilation (SODA, version 2.0.2) for the period of 1958–1997. Specifically, we look at the statistical relationship between the wind projection coefficients and climate indices and attempt to provide a physical explanation for the observed changes. It is found that the wind stress projection coefficients according to the oceanic baroclinic modes are different in terms of their magnitude and phase in the tropical Pacific, reflecting a specific forcing associated with each mode before and after the 1976 climate shift. Compared to that before the 1970s, the first baroclinic mode is had a greater effect on the interannual sea surface temperature due to equatorial wave dynamics, and there was an increased delayed response of the second baroclinic mode variability to the interannual atmospheric forcing after the late 1970s. This reflects changes in ENSO feedback processes associated with the climate shift. Our analysis further indicates that, after the late 1970s, there was a decrease in the wind stress forcing projecting onto the Ekman layer, which is associated with increased mixed-layer depth. This result suggests that the changes in the ENSO properties before and after the late 1970s are largely associated with the changes in the way in which the wind stress forcing is dynamically projected onto the surface layer of the tropical Pacific Ocean over interannual timescales. Full title: The influences of interannual stratification variability and wind stress forcing on ENSO before and after the 1976 climate shift
- 작성자Lee et al.
- 작성일2024.07.09
- 조회수10
- 2012
A projection of extreme climate events in the 21st century over East Asia using the Community Climate System Model 3

Abstract: A series of coupled atmosphere-ocean-land global climate model (GCM) simulations using the National Center for Atmospheric Research (NCAR) Community Climate System Model 3 (CCSM3) has been performed for the period 1870–2099 at a T85 horizontal resolution following the GCM experimental design suggested in the Intergovernmental Panel on Climate Change (IPCC) Fourth Assessment Report (AR4). First, a hindcast was performed using the atmospheric concentrations of three greenhouse gases (CO2, CH4, N2O) specified annually and globally on the basis of observations for the period 1870–1999. The hindcast results were compared with observations to evaluate the GCM’s reliability in future climate simulations. Second, climate projections for a 100-year period (2000–2099) were made using six scenarios of the atmospheric concentrations of the three greenhouse gases according to the A1FI, A1T, A1B, A2, B1, and B2 emission profiles of the Special Report on Emissions Scenarios. The present CCSM simulations are found to be consistent with IPCC’s AR4 results in the temporal and spatial distributions for both the present-day and future periods. The GCM results were used to examine the changes in extreme temperatures and precipitation in East Asia and Korea. The extreme temperatures were categorized into warm and cold events: the former includes tropical nights, warm days, and heat waves during summer (June–July–August) and the latter includes frost days, cold days, and cold surges during winter (December–January–February). Focusing on Korea, the results predict more frequent heat waves in response to future emissions: the projected percentage changes between the present day and the late 2090s range from 294% to 583% depending on the emission scenario. The projected global warming is predicted to decrease the frequency of cold extreme events; however, the projected changes in cold surge frequency are not statistically significant. Whereas the number of cold surges in the A1FI emission profile decreases from the present-day value by up to 24%, the decrease in the B1 scenario is less than 1%. The frequency and intensity of extreme precipitation events year-round were examined. Both the frequency and the intensity of these events are predicted to increase in the region around Korea. The present results will be helpful for establishing an adaptation strategy for possible climate change nationwide, especially extreme climate events, associated with global warming.
- 작성자Ho et al.
- 작성일2024.07.09
- 조회수8
- 2011
Browning in desert boundaries over Asia in the recent decades

Abstract: In this study, the changes in desert boundaries in Asia (Gobi, Karakum, Lut, Taklimakan, and Thar deserts) during the growing season (April–October) in the years 1982–2008 were investigated by analyzing the normalized difference vegetation index (NDVI), precipitation, and temperature. In the desert boundary regions, the domain mean NDVI values increased by 7.2% per decade in 1982–1998 but decreased by 6.8% per decade thereafter. Accordingly, the bare soil areas (or nonvegetated areas) of the inside of the desert boundaries contracted by 9.8% per decade in the 1990s and expanded by 8.7% per decade in the 2000s. It is noted that the five deserts experience nearly simultaneous NDVI changes although they cover a very diverse area of Asia. In contrast, changes in temperature and precipitation in the deserts show rather diverse results. In desert boundaries located along 40°N (Gobi, Taklimakan, and Karakum), the decadal changes in vegetation greenness were mainly related to regional climate during the entire analysis period. Precipitation increased in the 1990s, providing favorable conditions for vegetation growth (i.e., greening), but precipitation reduced (19 mm per decade) and warming intensified (0.7°C per decade) in the 2000s, causing less moisture to be available for vegetation growth (i.e., browning). In desert boundaries below 40°N (Lut and Thar), although an increase in precipitation (8 mm per decade) led to greening in the 1990s, local changes in precipitation and temperature did not necessarily cause browning in the 2000s. Observed multidecadal changes in vegetation greenness in the present study suggest that under significant global and/or regional warming, changes in moisture availability for vegetation growth in desert boundaries are an important factor when understanding decadal changes in areas vulnerable to desertification over Asia.
- 작성자Jeong et al.
- 작성일2024.07.09
- 조회수9
- 2011
Different characteristics of cold day and cold surge frequency over East Asia in a global warming situation

Abstract: This study investigates the changes in winter cold extreme events over East Asia in the present and future climates. Two distinct terms to indicate cold extreme events are analyzed: “cold day,” which describes a temperature below a certain threshold value (e.g., simply cold weather), and “cold surge,” which describes an abrupt temperature drop (e.g., relatively colder weather than a previous day). We analyze both observations and long-term climate simulations from 13 atmospheric and oceanic coupled global climate models (CGCMs). The geographical distribution of sea level pressure corresponding to a cold day (cold surge) is represented by a dipole (wave train) feature. Although cold day and cold surge show similar patterns of surface air temperature, they are induced by the out-of-phase sea level pressures. From the results of our analysis of a series of future projections for the mid and late twenty-first century using the 13 CGCMs, cold day occurrences clearly decrease with an increasing mean temperature (a correlation coefficient of −0.49), but the correlation between cold surge occurrences and the mean temperature is insignificant (a correlation coefficient of 0.08), which is supported by the same results in recent observation periods (1980–2006). Thus, it is anticipated that cold surge occurrences will remain frequent even in future warmer climate. This deduction is based on the future projections in which the change in the day-to-day temperature variability is insignificant, although the mean temperature shows significant increase. The present results suggest that living things in the future, having acclimatized to a warmer climate, would suffer the strong impact of cold surges, and hence the issue of vulnerability to cold surges should be treated seriously in the future.
- 작성자Park et al.
- 작성일2024.07.09
- 조회수8
- 2011
Diurnal circulations and their multi-scale interaction leading to rainfall over the SCS upstream of the Philippines...

Abstract: The morning diurnal precipitation maximum over the coastal sea upstream of the Philippines during intraseasonal westerly wind bursts is examined from observations and numerical model simulations. A well-defined case of precipitation and large-scale circulation over the coastal sea west of the Philippines during 17–27 June 2004 is selected as a representative case. The hypothesis is that the mesoscale diurnal circulation over the Philippines and a large-scale diurnal circulation that is induced by large-scale differential heating over Asian continent and the surrounding ocean interact to produce the offshore precipitation maximum during the morning. Three-hourly combined satellite microwave and infrared rainfall retrievals define the morning rainfall peak during this period, and then later the stratiform rain area extends toward the open sea. A control numerical simulation in which a grid-nudging four-dimensional data assimilation (FDDA) is applied to force the large-scale diurnal circulation represents reasonably well the morning rainfall maximum. An enhanced low-level convergence similar to observations is simulated due to the interaction of the local- and large-scale diurnal circulations. The essential role of the local-scale diurnal circulation is illustrated in a sensitivity test in which the solar zenith angle is fixed at 7 am to suppress this diurnal circulation. The implication for climate diagnosis or modeling of such upstream coastal sea precipitation maxima is that the diurnal variations of both the local- and the large-scale circulations must be taken into consideration. Full title: Diurnal circulations and their multi-scale interaction leading to rainfall over the South China Sea upstream of the Philippines during intraseasonal monsoon westerly wind bursts
- 작성자Park et al.
- 작성일2024.07.09
- 조회수8
- 2011
High-PM10 concentration episodes in Seoul, Korea: Background sources and related meteorological conditions

Abstract: This study examines the origin of and favorable meteorological conditions for high concentrations of particulate matter with a diameter <10 μm (PM10) in Seoul, Korea, in conjunction with systematic PM10 pathways. High-PM10 episodes, defined as days in which the 24-h mean PM10 exceeds 100 μg m−3, occurred 254 times during the period 2001–2008. Based on back trajectory and clustering analyses, the background sources of the high-PM10 in Seoul are categorized as external (176 episodes) and internal sources (78 episodes). The primary external sources include the industrial areas in inland China and the Gobi desert. The ratio of external to internal sources varies strongly according to the season, with highs in winter and spring and lows in summer. A composite analysis of meteorological factors for high-PM10 episodes with respect to the two sources (i.e., external and internal) suggests that an anomalous high pressure over Korea accompanied by an anomalous low pressure over the source regions favors both upper-level transport from the external source regions and the local accumulation of atmospheric PM10 in Seoul. The origins of high-PM10 episodes and their associated meteorological conditions found in this study can provide theoretical underpinnings for dust control strategies. Highlights: ► We examine the origin and the meteorologies of high-PM10 episodes in Seoul, Korea. ► The episodes by external sources are more frequent than those by internal sources. ► Wind and pressure fields determine both the occurrence and the type of episodes.
- 작성자Lee et al.
- 작성일2024.07.09
- 조회수9
- 2011