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2003 Vol. 20, No. 4

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Parameterization of the Non-Local Thermodynamic Equilibrium Source Function with Chemical Production by an Equivalent Two-Level Model
2003, 20(4): 487-495. doi: 10.1007/BF02915493
The classic two-level or equivalent two-level model that includes only the statistical equilibriumof radiative and thermal processes of excitation and quenching between two vibrational energy levelsis extended by adding chemical production to the rate equations. The modifications to the non-localthermodynamic equilibrium source function and cooling rate are parameterized by φc, which characterizesthe ratio of chemical production to collisional quenching. For applications of broadband emission of O3 at9.6 μm, the non-LTE effect of chemical production on the cooling rate and limb emission is proportionalto the ratio of O to O3. For a typical [O]/[O3], the maximum enhancements of limb radiance and coolingrate are about 15%-30% and 0.03-0.05 K day-1, respectively, both occurring near the mesopause regions.This suggests that the broadband limb radiance above ~80 km is sensitive to O3 density but not sensitiveto the direct cooling rate along the line-of-sight, which makes O3 retrieval feasible but the direct coolingrate retrieval difficult by using the O3 9.6 μm band limb emission.
Relationship between Sea Level Pressures of the Winter Tropical Western Pacific and the Subsequent Asian Summer Monsoon
WU Bingyi, WANG Dongxiao, HUANG Ronghui
2003, 20(4): 496-510. doi: 10.1007/BF02915494
Using monthly mean National Center for Environmental Prediction/National Center for AtmosphericResearch (NCEP/NCAR) reanalysis data for the period 1958-1996, based on a new circulation index inthe tropical western Pacific region, this paper investigates extreme winter circulation conditions in thenorthwestern Pacific and their evolution. The results show that the extreme winter circulation anomalyin the northwestern Pacific exhibits a strong association with those appearing in the high latitudes of theNorthern Hemisphere including the northern Asian continent, part of the Barents Sea, and the northeasternPacific. As the season progresses, an anticyclonic (cyclonic) circulation anomaly appearing in the north-western Pacific gradually moves northeastwards and extends westwards. Its axis in the west-east directionis also stretched. Therefore, easterly (westerly) anomalies in the southern part of the anticyclonic (cyclonic)circulation anomaly continuously expand westwards to the peninsula of India. Therefore, the South Asiansummer monsoon would be weaker (stronger). Simultaneously, another interesting phenomenon is theevolution of SLP anomalies. As the season progresses (from winter to the following summer), SLP anoma-lies originating from the tropical western Pacific gradually move towards, and finally occupy the Asiancontinent, and further influence the thermal depression over the Asian continent in the following summer.
Seasonal Characteristics of Precipitation in 1998 over East Asia as Derived from TRMM PR
FU Yunfei, LIN Yihua, Guosheng LIU, WANG Qiang
2003, 20(4): 511-529. doi: 10.1007/BF02915495
Precipitation radar data derived from the Tropical Rainfall Measuring Mission (TRMM) satelliteare used to study precipitation characteristics in 1998 over East Asia (10°-38°N, 100°-145°E), especiallyover mid-latitude land (continental land) and ocean (East China Sea and South China Sea). Results arecompared with precipitations in the tropics. Yearly statistics show dominant stratiform rain events overEast Asia (about 83.7% by area fraction) contributing to 50% of the total precipitation. Deep convectiverains contribute 48% to the total precipitation with a 13.7% area fraction. The statistics also show theunimportance of warm convective rain in East Asia, contributing 1.5% to the total precipitation with a2.7% area fraction. On a seasonal scale, the results indicate that the rainfall ratio of stratiform rain todeep convective rain is proportional to their rainfall pixel ratio. Seasonal precipitation patterns comparewell between Global Precipitation Climatology Project rainfall and TRMM PR measurements except insummer. Studies indicate a clear opposite shift of rainfall amount and events between deep convective andstratiform rains in the meridional in East Asia, which corresponds to the alternative activities of summermonsoon and winter monsoon in the region. The vertical structures of precipitation also exhibit strongseasonal variability in precipitation Contoured Rainrate by Altitude Diagrams (CRADs) and mean profilesin the mid-latitudes of East Asia. However, these structures in the South China Sea are of a tropical typeexcept in winter. The analysis of CRADs reveals a wide range of surface rainfall rates for most deepconvective rains, especially in the continental land, and light rain rate for most stratiform rains in EastAsia, regardless of over land or ocean.
Remote Sensing Parameterization of Land Surface Heat Fluxes over Arid and Semi-arid Areas
MA Yaoming, WANG Jiemin, HUANG Ronghui, WEI Guoan, Massimo MENENTI, SU Zhongbo, HU Zeyong, GAO Feng, WEN Jun
2003, 20(4): 530-539. doi: 10.1007/BF02915496
Dealing with the regional land surfaces heat fluxes over inhomogeneous land surfaces in arid and semi-arid areas is an important but not an easy issue. In this study, one parameterization method based onsatellite remote sensing and field observations is proposed and tested for deriving the regional land surfaceheat fluxes over inhomogeneous landscapes. As a case study, the method is applied to the Dunhuangexperimental area and the HEIFE (Heihe River Field Experiment, 1988-1994) area. The Dunhuang areais selected as a basic experimental area for the Chinese National Key Programme for Developing BasicSciences: Research on the Formation Mechanism and Prediction Theory of Severe Climate Disaster inChina (G1998040900, 1999-2003). The four scenes of Landsat TM data used in this study are 3 June 2000,22 August 2000, and 29 01- 2001 for the Dunhuang area and 9 07- 1991 for the HEIFE area. Theregional distributions of land surface variables, vegetation variables, and heat fluxes over inhomogeneouslandscapes in arid and semi-arid areas are obtained in this study.
The Relation between Atmospheric Intraseasonal Oscillation and Summer Severe Flood and Drought in the Changjiang-Huaihe River Basin
YANG Hui, LI Chongyin
2003, 20(4): 540-553. doi: 10.1007/BF02915497
The intraseasonal oscillation (ISO) is studied during the severe flood and drought years of theChangjiang-Huaihe River Basin with the NCEP/NCAR reanalysis data and the precipitation data inChina. The results show that the upper-level (200 hPa) ISO pattern for severe flood (drought) is charac-terized by an anticyclonic (cyclonic) circulation over the southern Tibetan Plateau and a cyclonic (anti-cyclonic) circulation over the northern Tibetan Plateau. The lower-level (850 hPa) ISO pattern is char-acterized by an anticyclonic (cyclonic) circulation over the area south of the Changjiang River, the SouthChina Sea, and the Western Pacific, and a cyclonic (anticyclonic) circulation from the area north of theChangjiang River to Japan. These low-level ISO circulation patterns are the first modes of the ISO windfield according to the vector EOF expansion with stronger amplitude of the EOF1 time coefficient in se-vere flood years than in severe drought years. The analyses also reveal that at 500 hPa and 200 hPa,the atmospheric ISO activity over the Changjiang-Huaihe River basin, North China, and the middle-highlatitudes north of China is stronger for severe flood than for severe drought. The ISO meridional windover the middle-high latitude regions can propagate southwards and meet with the northward propagatingISO meridional wind from lower latitude regions over the Changjiang-Huaihe River Basin during severeflood years, but not during severe drought years.
A Laboratory Model for the Flow in Urban Street Canyons Induced by Bottom Heating?
LIU Huizhi, LIANG Bin, ZHU Fengrong, ZHANG Boyin, SANG Jianguo
2003, 20(4): 554-564. doi: 10.1007/BF02915498
Water tank experiments are carried out to investigate the convection flow induced by bottom heatingand the effects of the ambient wind on the flow in non-symmetrical urban street canyons based on thePIV (Particle Image Visualization) technique. Fluid experiments show that with calm ambient wind,the flows in the street canyon are completely driven by thermal force, and the convection can reach theupper atmosphere of the street canyon. Horizontal and vertical motions also appear above the roofs ofthe buildings. These are the conditions which favor the exchange of momentum and air mass between thestreet canyon and its environment. More than two vortices are induced by the convection, and the complexcirculation pattern will vary with time in a wider street canyon. However, in a narrow street canyon, justone vortex appears. With a light ambient wind, the bottom heating and the associated convection resultin just one main vortex. As the ambient wind speed increases, the vortex becomes more organized and itscenter shifts closer to the leeward building.
Impact of Aircraft NOx Emission on NOx and Ozone over China
2003, 20(4): 565-574. doi: 10.1007/BF02915499
A three-dimensional global chemistry transport model (OSLO CTM2) is used to investigate theimpact of subsonic aircraft NOx emission on NOx and ozone over China in terms of a year 2000 scenario ofsubsonic aircraft NOx emission. The results show that subsonic aircraft NOx emission significantly affectsnorthern China, which makes NOx at 250 hPa increase by about 50 pptv with the highest percentage of60% in 01-, and leading to an ozone increase of 8 ppbv with 5% relative change in 04-. The NOxincrease is mainly attributed to the transport process, but ozone increase is produced by the chemicalprocess. The NOx increases by less than 10 pptv by virtue of subsonic aircraft NOx emission over China,and ozone changes less than 0.4 ppbv. When subsonic aircraft NOx emission over China is doubled, itsinfluence is still relatively small.
The 3-Hour-Interval Prediction of Ground-Level Temperature in South Korea Using Dynamic Linear Models
Keon-Tae SOHN, Deuk-Kyun RHA, Young-Kyung SEO
2003, 20(4): 575-582. doi: 10.1007/BF02915500
The 3-hour-interval prediction of ground-level temperature from +00 h out to +45 h in South Korea(38 stations) is performed using the DLM (dynamic linear model) in order to eliminate the systematicerror of numerical model forecasts. Numerical model forecasts and observations are used as input values ofthe DLM. According to the comparison of the DLM forecasts to the KFM (Kalman filter model) forecastswith RMSE and bias, the DLM is useful to improve the accuracy of prediction.
Simulation of Effects of Land Use Change on Climate in China by a Regional Climate Model
GAO Xuejie, LUO Yong, LIN Wantao, ZHAO Zongci, Filippo GIORGI
2003, 20(4): 583-592. doi: 10.1007/BF02915501
Climate effects of land use change in China as simulated by a regional climate model (RegCM2)are investigated. The model is nested in one-way mode within a global coupled atmosphere-ocean model(CSIRO R21L9 AOGCM). Two multi-year simulations, one with current land use and the other withpotential vegetation cover, are conducted. Statistically significant changes of precipitation, surface airtemperature, and daily maximum and daily minimum temperature are analyzed based on the differencebetween the two simulations. The simulated effects of land use change over China include a decrease ofmean annual precipitation over Northwest China, a region with a prevalence of arid and semi-arid areas;an increase of mean annual surface air temperature over some areas; and a decrease of temperature alongcoastal areas. Summer mean daily maximum temperature increases in many locations, while winter meandaily minimum temperature decreases in East China and increases in Northwest China. The upper soilmoisture decreases significantly across China. The results indicate that the same land use change 05-cause different climate effects in different regions depending on the surrounding environment and climatecharacteristics.
Association between Tropical Convection and Boreal Wintertime Extratropical Circulation in 1982/83 and 1988/89
Ja-Yeon MOON, Kyung-Ja HA
2003, 20(4): 593-603. doi: 10.1007/BF02915502
Boreal wintertime extratropical circulation is studied in relation to the tropical convection during the1982/83 El Nino and 1988/89 La Nina. The anomaly structure of 1982/83 and 1988/89 over the extratropicsreveals remarkably different features as the longitudinal tropical forcing region changes. The Rossby wavesource (Positive) shows the largest maximum over East Asia in both years due to the persistent heating fromthe western Pacific warm pool area. However, the sink term shows contrasting features over the subtropicsand extratropics between the two years. In the El Nino year, enhanced tropical convection over the easternPacific produces the Rossby wave sink at 10°N and shifted eastward over the North Pacific, while in theLa Nina year, the sink area is shifted westward over the North Pacific. The contrasting features betweenthe two events in mean-eddy interaction appears especially over the downstream area of the East AsianJet. The extension (retraction) of the meanflow eastward (westward) to the east (west) of the datelineis related with the effect of the westward (eastward) E-vector and the strengthening (weakening) of thenegative anomalies of the barotropic growth of kinetic energy. Hence, almost opposite characteristicsbetween the two events can explain the close relationship of tropical convection and the extratropicalinternal variability.
The Decade-Scale Climatic Forecasting in China
LIN Zhenshan, SHI Xiangsheng
2003, 20(4): 604-611. doi: 10.1007/BF02915503
Described is a new technique of decade-scale climatic forecasting, presented by a combination ofwavelet analysis and stochastic dynamics. The technique is also applied to diagnosing and forecasting theduration time of dry and wet climates in the decadal hierarchy of different areas in China. Results showthat in the decadal hierarchy, the north, southwest, and southeast of China are areas where various kindsof frequent climate disasters appear; droughts easily occur in the north and northwest, while floods oftenoccur in South China. Because this modeling technique is based on time series data, it can also be appliedin the modeling and forecasting of such time series as hydrology, earthquakes and ecology.
Initialization and Simulation of a Typhoon Using 4-Dimensional Variational Data Assimilation-Research on Typhoon Herb(1996)
ZHANG Xiaoyan, WANG Bin, JI Zhongzhen, Qingnong XIAO, ZHANG Xin
2003, 20(4): 612-622. doi: 10.1007/BF02915504
The MM5 and its four dimensional variational data assimilation (4D-Var) system are used in thispaper. Based on the National Centers for Environmental Prediction/National Center for AtmosphericResearch (NCEP/NCAR) reanalysis data, the authors generate an optimal initial condition for a typhoonby using the bogus data assimilation (BDA) scheme. BDA is able to recover many of the structuralfeatures of typhoons including a warm-core vertex, the correct center position, and the strong circulation.As a result of BDA using a bogus surface low, dramatic improvement is achieved in the 72 h predictionof typhoon Herb. Through several cases, the initialization by BDA effectively generates the harmoniousinner structure of the typhoon, but which is lacking in the original analysis field. Therefore the intensityforecast is improved greatly. Some improvements are made in the track forecast, but more work still needsto be done.
Generalized Nonlinear Subcritical Symmetric Instability
LU Weisong, SHAO Haiyan
2003, 20(4): 623-630. doi: 10.1007/BF02915505
Starting from nonlinear equations on the f-plane containing frictional dissipation under the Boussinesqapproximation, a new kind of generalized energy is proposed as the Lyapunov function, and averages aretaken as any functions of (x, z) instead of the commonly-used means of bilinear functions of (x, z), therebyresulting in a new criterion of generalized nonlinear symmetric stability. It shows that not only mustthe dissipative coefficient be greater than a certain critical value but the initial disturbance amplitudemust be synchronously smaller than another marginal value as well. It follows that the latter imposesa crucial constraint on the former, thus leading to the fact that when the amplitude is bigger comparedto another critical value, generalized nonlinear subcritical symmetrical instability 05- occur. The newcriterion contributes greatly to the improvement of the previous results of its kind.
A Laboratory Modeling of the Velocity Field in the Convective Boundary Layer with the Particle Image Velocimetry Technique
LI Pingyang, JIANG Weimei, SUN Jianning, YUAN Renmin
2003, 20(4): 631-637. doi: 10.1007/BF02915506
Based on the research of the convective boundary layer (CBL) temperature field in a convectivetank, this paper studies the characteristics of the CBL velocity field in the convective tank. Aluminiumpowder (400 order s) is used as a tracer particle in the application of the particle image velocimetry (PIV)technique. The experiment demonstrates: the velocity distribution in the mixed layer clearly possessesthe characteristics of CBL thermals; the velocity distribution in the top zone of the mixed layer showsentrainment layer characteristics; the vertical distribution of turbulent characteristic variables is reasonable,which is similar to field observations and other tank results; the error analysis demonstrates the validityof aluminium powder, which implies the reliability of the results.
Sensitivity Experiments of an Eastward-Moving Southwest Vortex to Initial Perturbations
2003, 20(4): 638-649. doi: 10.1007/BF02915507
Whether the initial conditious contain pronounced mesoscale signals is important to the simulation ofthe southwest vortex. An eastward-moving southwest vortex is simulated using the PSU/NCAR MM5. Amodest degree of success is achieved, but the most serious failure is that the formation and displacement ofthe simulated vortex in its early phase are about fourteen hours later than the observed vortex. Consideringthe relatively sparse data on the mesoscale vortex and in an attempt to understaud the cause of the forecastfailure, an adjoint model is used to examine the sensitivity of the southwest vortex to perturbations of initialconditions. The adjoint sensitivity indicates how small perturbations of model variables at the initial timein the model domain can influence the vortex. A large sensitivity for zonal wind is located under 400 hPa, alarge sensitivity for meridional wind is located under 500 hPa, a large sensitivity for temperature is locatedbetween 500 and 900 hPa, and almost all of the large sensitivity areas are located in the southwesternarea. Based on the adjoint sensitivity results, perturbations are added to initial conditions to improvethe simulation of the southwest vortex. The results show that the initial conditions with perturbatiouscan successfully simulate the formation and displacement of the vortex; the wind perturbations added tothe initial conditions appear to be a cyclone circulation under the middle level of the atmosphere in thesouthwestern area with an anticyclone circulation to its southwest; a water vapor perturbation added toinitial conditions can strengthen the vortex and the speed of its displacement.
Validation of Sea Level Data in the East Asian Marginal Seas:Comparison between TOPEX/POSEIDON Altimeter and In-Situ Tide Gauges
Yong-Hoon YOUN, Im Sang OH, Ki-Hyun KIM, Young-Hyang PARK, Jong Woo KIM
2003, 20(4): 650-660. doi: 10.1007/BF02915508
In an effort to assess the reliability of satellite altimeter systems, the authors conduct a comparativeanalysis of sea level data that were collected from the TOPEX/POSEIDON (T/P) altimeter and 10 tidegauges (TG) near the satellite passing ground tracks. The analysis is made using datasets collected frommarginal sea regions surrounding the Korean Peninsula at T/P cycles of 2 to 230, which correspond toOctober 1992 to December 1998. Proper treatment of tidal errors is a very critical step in data processingbecause the study area has very strong tide. When the T/P data are processed, the procedures of Parkand Gamberoni (1995) are adapted to reduce errors associated with the tide. When the T/P data areprocessed in this way, the alias periods of M2, S2, and K1 constituents are found to be 62.1, 58.7, and 173days repectively. The compatibility of the T/P and TG datasets are examined at various filtering periods.The results indicate that the low-frequency signals of the T/P data can be interpreted more safely withlonger filtering periods (such as up to the maximum selected value of 200 days). When RMS errors forthe 200-day low-pass filter period are compared with all 10 tidal stations, the values span the range of2.8 to 6.7 cm. The results of a correlation analysis for this filtering period also show a strong agreementbetween the T/P and TG datasets across all stations investigated (e.g., p-values consistently less than0.001 ). Hence according to the analysis, the conclusion is made that the analysis of surface sea level usingsatellite altimeter data can be made safely with reasonably extended filtering periods such as 200 days.