• 한국농림기상학회지
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• 제25권4호
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• pp.415-426
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• 2023

본 연구는 수치모델 바람 자료를 통해서, 중국 비래해충 발원지의 기압별 분포와 바람장미도를 확인하여 풍향과 풍속을 분석하였다. 사용한 수치모델은 Land-Atmosphere Modeling Package (LAMP) - WRF 자료이며, 시공간 해상도는 1시간 간격의 약 20 km 수평해상도 자료이다. 2021년도에 벼멸구와 애멸구가 동시에 관찰된 예찰일인 7월 16일을 대상으로 하였다. 예찰일을 포함하는 7월 8일부터 7월 17일까지 발원지와 우리나라에 850 hPa부터 925 hPa에 이르는 하층대기에 제트 기류가 발생하는지를 살펴보기 위하여 LAMP 바람의 동서, 남북, 연직 성분 자료를 이용하여 풍속을 분석하였다. 바람의 연직 분포결과 비래해충 발생 시기가 될 때 바람이 비래해충 유입에 유리하게 바뀌는 것이 확인되었다. 바람장미도의 분석 결과, 우리나라와 가까운 지점에서 바람의 약 30% 이상이 제트 기류였고, 다섯 지점의 제트 기류의 풍향은 상층보다 하층에서 대부분 우리나라와 일본으로 향하고 있었으며, HYSPLIT의 역궤적 추적을 통해서도 하층 제트가 비래해충의 국내 유입에 영향을 준 것으로 분석이 되었다. 이 연구는 원하는 지점에서의 하층 제트의 풍속과 풍향을 비래해충 발생 시기와 비발생 시기를 비교 분석한 것으로, 국내로 유입되는 비래해충의 시기와 바람 통로에 대한 수평 및 연직적 연관 분석에 도움을 줄 것이다. 국내 144개 시군 농업기술센터에서 운영 중인 공중 포충망 설치 지역에 대한 검토와 평가에도 활용될 수 있을 것이다.

• 대기
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• 제19권1호
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• pp.37-51
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• 2009

Kinematic characteristics of a heavy rainfall event occurred in Changma front are analyzed using synoptic weather charts, satellite imagery and NCEP(National Centers for Environmental Prediction) / NCAR(National Centers for Atmospheric Research) reanalysis data. The heavy rainfall is accompanied with mesoscale rain clouds developing over the Southwest region of Korea during the period from 0300 LST to 2100 LST 25 June 2006. The surface cyclone in the Changma front is generated and developed rapidly when it meets following vertical conditions: The maximum value of relative vorticity is appeared at 700 hPa and is extended gradually near the surface. It is thought that the vertical structure of relative vorticity is closely related with the descent of strong wind zone exceeding $10ms^{-1}$. The jet core at 200 hPa is shifted southward and extended downward and the low-level jet stream associated with upper-level jet stream appeared at 850 hPa. Kinematic features of heavy rainfall system at cyclone-generating point are as follows: In the generating stage of cyclone, the relative vorticity below 850 hPa increased and the convergence below 850 hPa and the divergence at 400 hPa are intensified by southward movement of jet core at 200 hPa. The heavy rainfall system seems to locate to the south of the exit region of upper-level jet streak; In the developing stage of cyclone, the relative vorticity below 850 hPa and the convergence near surface are further strengthened and upward vertical velocity between 850 hPa and 200 hPa is increased.

• Journal of Advanced Marine Engineering and Technology
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• 제18권1호
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• pp.81-91
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• 1994

Combustion noise involved with chemical heat release and turbulent process in turbopropulsion systems, gasturbine, industrial furnaces and internal engines is indeed noisy. The experimental study reported in this paper is made to identify a dominant combustion noise in jet flames. Gaseous propane and kerosene fuel have been used with air as the oxidizer in a different jet combustion systems. Combustion and aerodynamic noise are studied through far field sound pressure measurements in an anechoic chamber. And also mean temperature and velocities and turbulent intensities of both isothermal and reacting flow fields were measured. It is shown that axial mean velocity of reacting flow fields is higher about 1 to 3m/sec than that of cold flow in a gaseous combustor. As the gaseous fuel flow rate increases, the acoustic power increases. But the sound pressure level for the spray flame decreases with increasing equivalence ratio. The influence of temperature in the combustion fields due to chemical heat release has been observed to be a dominant noise source in the spray flame. The spectra of combustion noise in gaseous propane and kerosene jet flame show a predominantly low frequency and a broadband nature as compared with the noise characteristics in an isothermal air jet.

• 대한기계학회논문집A
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• 제25권12호
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• pp.2100-2108
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• 2001

The impinging tones by high-speed plane jets are experimentally investigated to study the edgetone characteristics. Experiment used a slit nozzle and a wedge system to generate edgetones. The jet in the experiment is varied from low to high subsonic speed to obtain the effect of the speed on the frequency characteristics of impinging tones. The experimental data obtained previously fur edgetones and platetones by various nozzles are compared with the present edgetone data. And the condition of tone generation, the frequency ranges, the effective source point and the sound pressure level are compared and discussed. It is found that the jet speed has no diect influence on the impinging tone characteristics. Regardless of the jet speed, the effective source point is about a quarter wavelength downstream from the edge tip. With increase in jet speed, the influence of the nozzle configuration is decreased and the operating frequencies show good coincidences by normalized parameters based on the slit thickness.

• Applied Science and Convergence Technology
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• 제26권6호
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• pp.201-207
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• 2017

An electron-excited temperature ($T_{ex}$) is not determined by the Boltzmann plots only with the spectral data of $4p{\rightarrow}4s$ in an Ar-plasma jet operated with a low frequency of several tens of kHz and the low voltage of a few kV, while $T_{ex}$ can be obtained at least with the presence of a high energy-level transition ($5p{\rightarrow}4s$) in the high-voltage operation of 8 kV. The optical intensities of most spectra that are measured according to the voltage and the measuring position of the plasma column increase or decay exponentially at the same rate as that of the intensity variation; therefore, the excitation temperature is estimated by comparing the relative optical-intensity to that of a high voltage. In the low-voltage range of an Ar-jet operation, the electron-excitation temperature is estimated as being from 0.61 eV to 0.67 eV, and the corresponding radical density of the Ar-4p state is in the order of $10^{10}{\sim}10^{11}cm^{-3}$. The variation of the excitation temperature is almost linear in relation to the operation voltage and the position of the plasma plume, meaning that the variation rates of the electron-excitation temperature are 0.03 eV/kV for the voltage and 0.075 eV/cm along the plasma plume.

• 한국해양학회지
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• 제20권2호
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• pp.28-39
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• 1985

저층 jet와 야간 최대 연안표층풍의 유도 mechanism을 텍사스주의 Port Aransas 와 Victoria지역에서 1976년 6월부터 1980년 8월까지 관측된 바람자료를 사용하여 경압모델에 의해 연구되었다. 이모델은 forcing function인 종관 및 중기압 경도, 마찰력과 대기안정도를 고려하여 개발된다. 연구결과는 야간최대 연안표층풍 에 대해 저층 jet가 95%의 출현빈도를 보여준다. 여름철에는 경사지형에 의한 경압 성이 thermal field의 일변화를 초래한다. 이 온도풍이 낮에는 탁월한 남풍의 풍속을 감소시키고 밤에는 증가시킨 다. 야간대기안정도는 마찰력 유리를 유도하므로 야간 저층 jet를 강화한다. 해안에서는 중립안정도가 지배적이고 또 저층 jet로부터 운동 량의 연직전이는 야간 최대연안표층풍을 형성한다. 저층 jet의 출현고도는 역전층과 의 뚜렷한 관계를 보여주지 않으며, 이 모델에 의한 계산결과는 관측치와 잘 일치 한다.

• 한국수자원학회:학술대회논문집
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• 한국수자원학회 2005년도 학술발표회 논문집
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• pp.9-18
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• 2005

In order to systematically and visually understand well-known but qualitative and rotatively complicated relationships between synoptic fields in the BAIU season and heavy rainfall events in Japan, these synoptic fields were classified using the Self-Organizing Map (SOM) algorithm. This algorithm can convert complex nonlinear features into simple two-dimensional relationships, and was followed by the application of the clustering techniques of the U-matrix and the K-means. It was assumed that the meteorological field patterns be simply expressed by the spatial distribution of wind components at the 850 hPa level and Precipitable Water (PW) in the southwestern area including Kyushu in Japan. Consequently, the synoptic fields could be divided into eight kinds of patterns (clusters). One of the clusters has the notable spatial feature represented by high PW accompanied by strong wind components known as Low-Level Jet (LLJ). The features of this cluster indicate a typical meteorological field pattern that frequently causes disastrous heavy rainfall in Kyushu in the rainy season. From these results, the SOM technique may be an effective tool for the classification of complicated non-linear synoptic fields.

• 통합자연과학논문집
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• 제8권3호
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• pp.221-232
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• 2015

In this study, the vertical characteristics of wind were analyzed using the horizontal wind, vertical wind, and vertical wind shear, which are generated from a wind profiler during concentrated heavy rain, and the quantitative characteristics of concentrated heavy rain were analyzed using CAPE, SWEAT, and SRH, among the stability indexes. The analysis of the horizontal wind showed that 9 cases out of 10 had a low level jet of 25 kts at altitudes lower than 1.5 km, and that the precipitation varied according to the altitude and distribution of the low-level jet. The analysis of the vertical wind showed that it ascended up to about 3 km before precipitation. The analysis of the vertical wind shear showed that it increased up to a 1 km altitude before precipitation and had a strong value near 3 km during heavy rains. In the stability index analysis, CAPE, which represents thermal buoyancy, and SRH, which represents dynamic vorticity, were used for the interpretation of the period of heavy rain. As SWEAT contains dynamic upper level wind and thermal energy, it had a high correlation coefficient with concentrated-heavy-rain analysis. Through the case studies conducted on August 12-13, 2012, it was confirmed that the interpretation of the prediction of the period of heavy rain was possible when using the intensive observation data from a wind profiler and the stability index.

• 한국환경과학회지
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• 제11권2호
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• pp.111-120
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• 2002

Asian dust(or yellow sand) occurs mainly in spring and occasionally in winter in east Asia, when the weather conditions are under an upper trough/cut-off low and surface high/low pressure system during blocking episode days associated with the stationary patterns of the upper level jet stream. The transport mechanism for Asian dust during the blocking episode days in spring 2001 was analyzed using the TOMS aerosol index and meteorological mesoscale model 5(MM5). Based on the E vector, an extension of an Eliassen-Palm flux, the blocking episode days were found to be associated with the development of an upper cut-off low and surface cyclones. Concurrently, the occurrence of dust storms was also determined by strong cold advection at the rear of a jet streak, which exhibited a maximum wind speed within the upper jet stream. As such, the transport mechanism for Asian dust from China was due to advection of the isentropic potential vorticity(IPV) and isentropic surfaces associated with tropopause folding. The transport heights for Asian dust during the blocking episode days were found to be associated with the distribution of the isentropes below the IPV At the same time, lee waves propagated by topography affected the downward motion and blocking of Asian dust in China. The Asian dust transported from the dust source regions was deposited by fallout and rain-out with a reinforcing frontogenesis within a surface cyclone, as determined from satellite images using TOMS and GMS5. Accordingly, these results emphasize the importance of forecasting jet streaks, the IPV, and isentropes with geopotential heights in east Asia.

• 한국지구과학회:학술대회논문집
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• 한국지구과학회 2004년도 춘계학술발표회 논문집
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• pp.39-40
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• 2004