• Title/Summary/Keyword: Polar mean

Search Result 282, Processing Time 0.027 seconds

Review on the impact of Arctic Amplification on winter cold surges over east Asia (북극 온난화 증폭이 겨울철 동아시아 한파 발생에 미치는 영향 고찰)

  • Seong-Joong Kim;Jeong-Hun Kim;Sang-Yoon Jun;Maeng-Ki Kim;Solji Lee
    • The Korean Journal of Quaternary Research
    • /
    • v.33 no.1_2
    • /
    • pp.1-23
    • /
    • 2021
  • In response to the increase in atmospheric carbon dioxide and greenhouse gases, the global mean temperature is rising rapidly. In particular, the warming of the Arctic is two to three times faster than the rest. Associated with the rapid Arctic warming, the sea ice shows decreasing trends in all seasons. The faster Arctic warming is due to ice-albedo feedback by the presence of snow and ice in polar regions, which have higher reflectivity than the ocean, the bare land, or vegetation, higher long-wave heat loss to space than lower latitudes by lower surface temperature in the Arctic than lower latitudes, different stability of atmosphere between the Arctic and lower latitudes, where low stability leads to larger heat losses to atmosphere from surface by larger latent heat fluxes than the Arctic, where high stability, especially in winter, prohibits losing heat to atmosphere, increase in clouds and water vapor in the Arctic atmosphere that subsequently act as green house gases, and finally due to the increase in sensible heat fluxes from low latitudes to the Arctic via lower troposphere. In contrast to the rapid Arctic warming, in midlatitudes, especially in eastern Asia and eastern North America, cold air outbreaks occur more frequently and last longer in recent decades. Two pathways have been suggested to link the Arctic warming to cold air outbreaks over midlatitudes. The first is through troposphere in synoptic-scales by enhancing the Siberian high via a development of Rossby wave trains initiated from the Arctic, especially the Barents-Kara Seas. The second is via stratosphere by activating planetary waves to stratosphere and beyond, that leads to warming in the Arctic stratosphere and increase in geopotential height that subsequently weakens the polar vortex and results in cold air outbreaks in midlatitudes for several months. There exists lags between the Arctic warming and cold events in midlatitudes. Thus, understanding chain reactions from the Arctic warming to midlatitude cooling could help improve a predictability of seasonal winter weather in midlatitudes. This study reviews the results on the Arctic warming and its connection to midlatitudes and examines the trends in surface temperature and the Arctic sea ice.

A Study on Biomechanical Noise Reduction Technique Using Length Information (길이 정보를 이용한 생체 잡음 제거 기술에 관한 연구)

  • Gang, Sin-Gil;Yun, Yong-San;Park, Jae-Hui
    • Transactions of the Korean Society of Mechanical Engineers A
    • /
    • v.24 no.7 s.178
    • /
    • pp.1643-1649
    • /
    • 2000
  • When markers attached to body segment are captured by camera, they generally have many noises due to intrinsic biomechanical characteristics. In this study, one technique to reduce these noises is suggested, which constructs a local coordinates of the markers using time-mean lengths of the measured markers and calculates a linear transformation matrix of the interesting body using least square error technique. This matrix is decomposed into two matrices of rotation and flexibility. Suggested method does well for 3 markers or more, and shows consistent results without regard to choice of reference axis.

Comparisons of Ocean Currents Observed from Drifters and TP/ERS in the East Sea

  • Lee, Dong-Kyu;Niiler, Pearn P.;Suk, Moon-Sik
    • Ocean and Polar Research
    • /
    • v.23 no.2
    • /
    • pp.133-139
    • /
    • 2001
  • Ocean currents estimated from sea height anomalies derived from inter-calibrated TP/ERS are compared with daily mean currents measured with satellite-tracked drifters. The correlation coefficient between the geostrophic current from TP/ERS and surface current at 15 m depth from drifter tracks was found to be about 0.5. Due to the limitation of satellite ground tracks, small scale eddies less than 80 km are poorly resolved from TP/ERS. One of the interesting results of this study is that coastal currents along the eastern coast of Korea were well reproduced from sea height anomalies when the coastal currents were developed in association with eddies near the South Korean coast. The eddy kinetic energy (EKE) estimated from drifters, TP/ERS, and a numerical model are also compared. The EKE estimated from drifters was about 22 % higher than EKE calculated from TP/ERS. The pattern of low EKE level in the northern basin and high EKE level in the southern East Sea is shown in the EKE estimates derived from both the drifters and TP/ERS.

  • PDF

The Warm Eddy in the East Korean Bight

  • Shin, Chang-Woong;Kim, Cheol-Soo;Byun, Sang-Kyung
    • Ocean and Polar Research
    • /
    • v.23 no.1
    • /
    • pp.1-10
    • /
    • 2001
  • Sea surface temperature derived from infrared images of NOAA satellites showed a warm eddy in the East Korean Bight(EKB) or Donghan Man during the winter 1997${\sim}$2000. To describe the warm eddy in the EKB, hydrographic data collected in 1934 and 1936 were also analyzed. The center of the warm eddy was located at about $39^{\circ}N$ and $129^{\circ}E$. The temperature and salinity of the eddy was about $4.0^{\circ}C$ and 34.0 psu, respectively, at 100m depth. The eddy rotated anticyclonically with a geostrophic current speed of about 20 cm/s. The mean state calculated from the data of 1922${\sim}$1960 showed the existence of a warm eddy over the EKB in winter. The eddy persists until late spring, and disappears from the previous location in summertime, only to be seen again in autumn.

  • PDF

Precipitation Anomalies Around King Sejong Station, Antarctica Associated with E1Niño/Southern Oscillation

  • Kwon, Tae-Yong;Lee, Bang-Yong
    • Ocean and Polar Research
    • /
    • v.24 no.1
    • /
    • pp.19-31
    • /
    • 2002
  • Precipitation variability around King Sejong Station related with E1 $Ni\~{n}o$/Southern Oscillation (ENSO) is evaluated using the gauge-based monthly data of its neighboring stations. Though three Ant-arctic Stations of King Sejong (Korea), Frei (Chile), and Artigas (Uruguay) are all closely located within 10 km, their precipitation data show mostly insignificant positive or rather negative correlations among them in the annual, seasonal and monthly precipitation. This result indicates that there are locally large variations in the distribution of precipitation around King Sejong Station. The monthly data of Frei Station for 31 years (1970-2000) are analyzed for examining the ENSO signal in precipitation because of its longer precipitation record compared to other two stations. From the analysis of seasonal precipitation, it is seen that there is a tendency of less precipitation than the average during E1 $Ni\~{n}o$ events. This dryness is more distinct in fall to spring seasons, in which the precipitation decreases down to about 30% of seasonal mean precipitation. However, the precipitation signal related with La $Ni\~{n}a$ events is not significant. From the analysis of monthly precipitation, it is found that there is a strong negative correlation during 1980s and in the late 1990s, and a weak positive correlation in the early 1990s between normalized monthly precipitation at Frei Station and Sea Surface Temperature (SST) anomalies in the $Ni\~{n}o$ 3.4 region. However, this relation may be not applied over the region around King Sejong Station, but at only one station, Frei.

Tower-based Flux Measurement Using the Eddy Covariance Method at Ieodo Ocean Research Station (이어도해양과학기지에서의 에디 공분산 방법을 이용한 플럭스 관측)

  • Lee, Hee-Choon;Lee, Bang-Yong;Kim, Joon;Shim, Jae-Seol
    • Ocean and Polar Research
    • /
    • v.26 no.2
    • /
    • pp.145-154
    • /
    • 2004
  • Surface energy and $CO_2$ fluxes have been measured over an ocean at Ieodo Ocean Research Station of KORDI since May 2003. Eddy covariance technique, which is a direct flux measurement, is used to quantitatively understand the interaction between the ocean surface and the atmospheric boundary layer. Although fluxes were continuously measured during the period from May 2003 to February 2004, the quality control of these data yielded <20% of data retrieval. The atmospheric stability did not show any distinct dirunal patterns and remained near-neutral to stable from May to June but mostly unstable during fall and winter in 2003. Sensible heat flux showed a good correlation with the difference between the sea water temperature and the air temperature. The maximum fluxes of sensible heat and latent heat were $120Wm^{-2}$ and $350Wm^{-2}$ respectively, with an averaged Bowen ratio of 0.2. The ocean around the tower absorbed $CO_2$ from the atmosphere and the uptake rates showed seasonal variations. Based our preliminary results, the daytime $CO_2$ flux was steady with an average of $-0.1 mgCO_2m^{-2}s^{-1}$ in summer and increased in winter. The nighttime $CO_2$ uptake was greater and fluctuating, reaching up to $-0.1 mgCO_2m^{-2}s^{-1}$ but these data require further examination due to weak turbulent mixing at nighttime. The magnitude of $CO_2$ flux was positively correlated with the half hourly changes in horizontal mean wind speed. Due to the paucity of quality data, further data collection is needed for more detailed analyses and interpretation.

The Operational Procedure on Estimating Typhoon Center Intensity using Meteorological Satellite Images in KMA

  • Park, Jeong-Hyun;Park, Jong-Seo;Kim, Baek-Min;Suh, Ae-Sook
    • Proceedings of the KSRS Conference
    • /
    • v.1
    • /
    • pp.278-281
    • /
    • 2006
  • Korea Meteorological Administration(KMA) has issued the tropical storm(typhoon) warning or advisories when it was developed to tropical storm from tropical depression and a typhoon is expected to influence the Korean peninsula and adjacent seas. Typhoon information includes current typhoon position and intensity. KMA has used the Dvorak Technique to analyze the center of typhoon and it's intensity by using available geostationary satellites' images such as GMS, GOES-9 and MTSAT-1R since 2001. The Dvorak technique is so subjective that the analysis results could be variable according to analysts. To reduce the subjective errors, QuikSCAT seawind data have been used with various analysis data including sea surface temperature from geostationary meteorological satellites, polar orbit satellites, and other observation data. On the other hand, there is an advantage of using the Subjective Dvorak Technique(SDT). SDT can get information about intensity and center of typhoon by using only infrared images of geostationary meteorology satellites. However, there has been a limitation to use the SDT on operational purpose because of lack of observation and information from polar orbit satellites such as SSM/I. Therefore, KMA has established Advanced Objective Dvorak Technique(AODT) system developed by UW/CIMSS(University of Wisconsin-Madison/Cooperative Institude for Meteorological Satellite Studies) to improve current typhoon analysis technique, and the performance has been tested since 2005. We have developed statistical relationships to correct AODT CI numbers according to the SDT CI numbers that have been presumed as truths of typhoons occurred in northwestern pacific ocean by using linear, nonlinear regressions, and neural network principal component analysis. In conclusion, the neural network nonlinear principal component analysis has fitted best to the SDT, and shown Root Mean Square Error(RMSE) 0.42 and coefficient of determination($R^2$) 0.91 by using MTSAT-1R satellite images of 2005. KMA has operated typhoon intensity analysis using SDT and AODT since 2006 and keep trying to correct CI numbers.

  • PDF

Assessment of Stratospheric Prediction Skill of the GloSea5 Hindcast Experiment (GloSea5 모형의 성층권 예측성 검증)

  • Jung, Myungil;Son, Seok-Woo;Lim, Yuna;Song, Kanghyun;Won, DukJin;Kang, Hyun-Suk
    • Atmosphere
    • /
    • v.26 no.1
    • /
    • pp.203-214
    • /
    • 2016
  • This study explores the 6-month lead prediction skill of stratospheric temperature and circulations in the Global Seasonal forecasting model version 5 (GloSea5) hindcast experiment over the period of 1996~2009. Both the tropical and extratropical circulations are considered by analyzing the Quasi-Biennial Oscillation (QBO) and Northern Hemisphere Polar Vortex (NHPV). Their prediction skills are quantitatively evaluated by computing the Anomaly Correlation Coefficient (ACC) and Mean Squared Skill Score (MSSS), and compared with those of El Nino-Southern Oscillation (ENSO) and Arctic Oscillation (AO). Stratospheric temperature is generally better predicted than tropospheric temperature. Such improved prediction skill, however, rapidly disappears in a month, and a reliable prediction skill is observed only in the tropics, indicating a higher prediction skill in the tropics than in the extratropics. Consistent with this finding, QBO is well predicted more than 6 months in advance. Its prediction skill is significant in all seasons although a relatively low prediction skill appears in the spring when QBO phase transition often takes place. This seasonality is qualitatively similar to the spring barrier of ENSO prediction skill. In contrast, NHPV exhibits no prediction skill beyond one month as in AO prediction skill. In terms of MSSS, both QBO and NHPV are better predicted than their counterparts in the troposphere, i.e., ENSO and AO, indicating that the GloSea5 has a higher prediction skill in the stratosphere than in the troposphere.

Extreme Enhancements in GPS TEC on 8 and 10 November 2004

  • Chung, Jong-Kyun;Jee, Gun-Hwa;Kim, Eo-Jin;Kim, Yong-Ha;Cho, Jung-Ho
    • Bulletin of the Korean Space Science Society
    • /
    • 2010.04a
    • /
    • pp.30.2-30.2
    • /
    • 2010
  • It is a mistaken impression that the midlatitude ionosphere was a very stable region with well-known morphology and physical mechanism. However, the large disturbances of midlatitude ionospheric contents in response to global thermospheric changes during geomagnetic storms are reported in recent studies using global GPS TEC map and space-born thermospheric UV images, and its importance get higher with the increasing application areas of space navigation systems and radio communication which are mostly used in the midlatitudes. Positive and negative storm phases are used to describe increase and decrease of ionospheric electron density. Negative storms result generally from the enhanced loss rate of electron density according to the neutral composition changes which are initiated by Joule heating in high-latitudes during geomagnetic storms. In contrast, positive ionospheric storms have not been well understood because of rare measurements to explain the mechanisms. The large enhancements of ground-based GPS TEC in Korea were observed on 8 and 10 November 2004. The positive ionospheric storm was continued except for dawn on 8 November, and its maximum value is ~65 TECU of ~3 times compared with the monthly mean TEC values. The other positive phase on 10 November begin to occur in day sector and lasted for more than 6 hours. The O/N2 ratios from GUVI/TIMED satellite show ~1.2 in northern hemisphere and ~0.3 in southern hemisphere of the northeast Asian sector on 8 and 10 November. We suggest the asymmetric features of O/N2 ratios in the Northeast Asian sector may play an important role in the measured GPS TEC enhancements in Korea because global thermospheric wind circulation can globally change the chemical composition during geomagnetic storms.

  • PDF

Acoustic Target Strength Characteristics of Two Species of Multiple Jellyfishes, Aurelia aurita and Cyanea nozakii, in the Southern Coast of Korea (남해 연안에 분포하는 해파리(Aurelia aurita, Cyanea nozakii)의 복수 개체에 의한 음향 표적강도 특성)

  • Kang, Don-Hyug;Kim, Jung-Hun;Lim, Seon-Ho
    • Ocean and Polar Research
    • /
    • v.32 no.2
    • /
    • pp.113-122
    • /
    • 2010
  • Understanding the abundance and distribution of massive jellyfish is necessary to forecast where or when their blooms will happen. The acoustic technique is one of the most useful methods of obtaining information if the acoustic characteristics of the targets are known. This study was conducted to determine the acoustic target strength (TS, dB) of two jellyfish species, Aurelia aurita and Cyanea nozakii, in the southern coast of Korea. For the ex situ measurements, 120, 200, and 420 kHz split beam transducers were used, and jellyfish with various bell lengths were arranged to prepare multiple jellyfish. Under 2 vertical individuals, the mean TS for multiple A. aurita at 120, 200, and 420 kHz was -72.7, -71.7, and -68.2 dB, respectively. In the case of 5 vertical individuals, the mean TS of the species was -71.3, -68.2, and -62.0 dB. Finally, the mean TS of C. nozakii at 120, 200, and 200 kHz was -62.0, -60.3, and -58.2 dB under 2 individuals and -58.1, -57.4, and -54.0 dB under 4 individuals, respectively. For both species, higher numbers of jellyfish resulted in a higher TS. In addition, higher frequencies were associated with a higher TS for the same jellyfish. These TS results for two species can be used as essential data for the acoustic detection of jellyfish in an open ocean or coastal area.