Jai-Ho Oh

A teleconnection pattern in upper-level meridional wind over the North African and Eurasian continent in summer

One-point correlation analysis on upper-level meridional wind identified the existence of ateleconnection pattern in July, which emerges from North Africa to East Asia along the westerlyjet in the middle latitudes. We examined the spatial and temporal structures of this teleconnectionpattern, and found the unique characteristics rather different from the patterns in otherelements such as geopotential height, streamfunction and vorticity. We also investigated therelationship between this teleconnection and precipitation, and suggested that the teleconnectionis a possible linkage of the EASM to the Indian monsoon, and even to subtropical heatinganomalies over Atlantic.

Response of global warming on regional climate change over Korea: An experiment with the MM5 model

[1]xa0This study is to investigate changes in regional surface climate arising from global warming with MM5 downscaling simulation for the period 1971–2100. The main focus is on the drought conditions over Korea. Palmer Drought Severity Index (PDSI) is utilized as a measure of drought severity. The important findings show the increase of surface air temperature by 6°C and precipitation by 25% over Korea at the end of the 21st century. The increasing trend of temperature is associated with an increasing trend of evapotranspiration and precipitation. Climatological precipitation amount appropriate for existing conditions is larger than the precipitation amounts. Hence, it actually produces deficit in precipitation. This exhibits a negative PDSI. As a result droughts are expected to be severe and frequent. Better resolved topography in MM5 induces large changes in local precipitation compared with temperature. Consequently peaks of negative PDSI anomalies appear over southern parts of Korea, where a large reduction in precipitation is noticed in addition to warming.

Interpretation of the Transient Variations in the Time Series of Precipitation Amounts in Seoul, Korea. Part I: Diurnal Variation

Abstract Characteristics of temporal variations of precipitation for Seoul, Korea, have been examined using a 220-yr record. Precipitation records from modern rain gauges were used for 1908–96 together with the traditional Korean rain gauge precipitations for 1777–1907. The precipitation time series was partitioned into three precipitation regimes: wet period 1 (WP1; 1783–1883), the dry period (DP; 1884–1910), and wet period 2 (WP2; 1911–96). The basic features of the records were examined, and the diurnal variations derived from hourly precipitation were investigated. There were similarities between the statistical characteristics of the time series for WP1 and WP2, but the DP showed many statistical characteristics different from WP1 and WP2. Diurnal cycles derived from the hourly precipitation rates in Seoul are generally consistent with previous observations in maritime areas, but some differences are apparent between the two WPs and the DP in the mean diurnal cycle and its seasonal variation. The WPs...

Probabilistic interpretation of regression-based downscaled seasonal ensemble predictions with the estimation of uncertainty

[1]xa0A regression-based method of statistical downscaling from global multimodel ensemble (MME) forecasts has been developed. This method is appropriate for seasonal forecasts at stations with the use of model outputs as predictors; it refers to a technique that is known as “model output statistics” (MOS). Downscaled forecasts are formulated in terms of tercile probabilities based on the probabilistic interpretation of the forecast uncertainty. The novelty of the method is in the estimation of uncertainties originating from both regression and ensemble spread of model forecasts within the framework of the regression analysis. The method has been tested on the prediction of wintertime temperature and precipitation for 60 Korean stations by downscaling from the MME forecasts of 850 hPa temperature, sea level pressure, and 500 hPa geopotential height. Different sources of uncertainty associated with regression and ensemble spread have been evaluated and their contributions compared. It is shown that although the uncertainty associated with the deviation from the linear model is usually the largest, a comparable contribution to the uncertainty can come from the ensemble spread. Verification assessments of the method show that downscaled probabilistic MME forecasts essentially outperform the forecasts interpolated from the raw model predicted anomalies for both temperature and precipitation.

A parameterization of the evaporation of rainfall

Abstract In this study we develop theoretical expressions for the rainfall rate, P(z), and the total evaporation rate from cloud base to a level z below cloud base, E(z). The resultant parameterization for the total evaporation is given by E(z) = CPα(0)Ψ(z), where P(0) is the rainfall rate at cloud base, α and C are undetermined parameters, and Ψ(z) is a function of z. The latter is determined for the cases of constant relative humidity and constant absolute humidity below cloud base which correspond approximately to stratiform and cumuloform clouds, respectively. The parameters α and C are determined from radar observations of the rain failing from continental convective cells in central South Africa. The resultant values are α = 0.606 and C = 2.63 × 10−2 for P(0) and E(z) in millimeters per hour. Subsequent analyses of other radar observations utilizing the method developed in this study are needed to obtain corresponding evaporation parameterizations for cumuloform precipitation in other climatic regim...

IDentification Key Based AAA Mechanism in Mobile IP Networks

Mobile IP proposed by IETF supports continuous services for a mobile node (MN) based on its capability to roam around foreign domains. Recently the significance of the security for MN has been recognized. When it roams around a foreign domain, the authentication, authorization, and accounting (AAA) for the MN must be done at the foreign domain. For this reason, the IETF suggests that the existence of some servers capable of performing AAA services could help. In this paper, we propose a new mobile initiated handoff mechanism using an IDentification Key (IDK) that supports authentication and authorization for the MN, and reduces delay and the risk in authentication. The performance evaluation results show that the use of IDK for an MN in AAA model reduces the latency up to 40% while maintaining the similar level of security to the previous works.

Eastern Asian hydrometeorology simulation using the Regional Climate System Model

Abstract We present the hydrometeorology of eastern Asia during April 1995 simulated by the Regional Climate System Model. The amount and location of simulated monthly precipitation agrees well with observations. Soil water content variation was closely correlated with precipitation. Land-surface evaporation and the surface energy budget were strongly controlled by soil moisture content. A sensitivity test with reduced initial soil moisture content suggested that near-surface soil moisture spins up quickly after heavy precipitation events. However, variations in the initial soil moisture field may alter details of the simulated precipitation which can introduce further complexity in climate simulations.

Summer monsoon rainfall variability over North East regions of India and its association with Eurasian snow, Atlantic Sea Surface temperature and Arctic Oscillation

This observational study during the 29-year period from 1979 to 2007 evaluates the potential role of Eurasian snow in modulating the North East-Indian Summer Monsoon Rainfall with a lead time of almost 6xa0months. This link is manifested by the changes in high-latitude atmospheric winter snow variability over Eurasia associated with Arctic Oscillation (AO). Excessive wintertime Eurasian snow leads to an anomalous cooling of the overlying atmosphere and is associated with the negative mode of AO, inducing a meridional wave-train descending over the tropical north Atlantic and is associated with cooling of this region. Once the cold anomalies are established over the tropical Atlantic, it persists up to the following summer leading to an anomalous zonal wave-train further inducing a descending branch over NE-India resulting in weak summer monsoon rainfall.

Can the Southern annular mode influence the Korean summer monsoon rainfall

We demonstrate that a large-scale longitudinally symmetric global phenomenon in the Southern Hemisphere sub-polar region can transmit its influence over a remote local region of the Northern Hemisphere traveling more than 100° of latitudes (from ~70°S to ~40°N). This is illustrated by examining the relationship between the Southern Annular Mode (SAM) and the Korean Monsoon Rainfall (KMR) based on the data period 1983-2013. Results reveal that the May-June SAM (MJSAM) has a significant in-phase relationship with the subsequent KMR. A positive MJSAM is favorable for the summer monsoon rainfall over the Korean peninsula. The impact is relayed through the central Pacific Ocean. When a negative phase of MJSAM occurs, it gives rise to an anomalous meridional circulation in a longitudinally locked air-sea coupled system over the central Pacific that propagates from sub-polar to equatorial latitudes and is associated with the central Pacific warming. The ascending motion over the central Pacific descends over the Korean peninsula during peak-boreal summer resulting in weakening of monsoon rainfall. The opposite features prevail during a positive phase of SAM. Thus, the extreme modes of MJSAM could possibly serve as a predictor for ensuing Korean summer monsoon rainfall.

Possible teleconnections between East and South Asian summer monsoon precipitation in projected future climate change

The present paper examined the teleconnections between two huge Asian summer monsoon components (South and East Asia) during three time slices in future: near-(2010–2039), mid-(2040–2069) and far-(2070–2100) futures under the RCP4.5 and RCP8.5 scenarios. For this purpose, a high-resolution atmospheric general circulation model is used and integrated at 40xa0km horizontal resolution. To get more insight into the relationships between the two Asian monsoon components, we have studied the spatial displaying correlation coefficients (CCs) pattern of precipitation over the entire Asian monsoon region with that of South Asia and three regions of East Asia (North China, Korea–Japan and Southern China) separately during the same three time slices. The possible factors responsible for these teleconnections are explored by using mean sea level pressure (MSLP) and wind fields at 850xa0hPa. The CC pattern of precipitation over South Asia shows an in-phase relationship with North China and an out-of-phase relationship with Korea–Japan, while precipitation variations over Korea–Japan and Southern China exhibit an out-of-phase relationship with South Asia. The CCs analysis between the two Asian blocks during different time slices shows the strongest CCs during the near and far future with the RCP8.5 scenario. The CC pattern of precipitation over Korea–Japan and Southern China with the wind (at 850xa0hPa)xa0and MSLP fields indicate that the major parts of the moisture over Korea–Japan gets transported from the west Pacific along the western limb of NPSH, while the moisture over Southern China comes from the Bay of Bengal and South China Seas for good monsoon activity.