PROGRESS OF MARINE METEOROLOGY STUDIES
ACROSS THE NEW CENTURY ①
WANG Dongxiao1,2, QIN Zenghao 3 and SHI Ping 1
1. LED, South China Sea Institute of Oceanology, Guangzhou 510301, China
2. Guangzhou Institute of Tropical & Oceanic Meteorology, Guangzhou 510080, China
3. Shanghai Inst. of Typhoon, Shanghai 200030, China
In this paper the progresses of marine meteorology studies achieved in China in the four year period from 1998 to 2002 were summarized upon six directions, i. e., air-sea flux, marine meteorology in high latitude, marine disasters, connection between ocean and weather/climate in China, remote sensing application and new methodology in marine meteorology. Compared to the previous ones, these studies adopted much more first-hand data sets and more scientific issues were involved. As an exciting remark, there are so many contributions done by the young scientists.
Key words: marine meteorology in China, field observation, marine disaster, remote sensing application
Marine meteorology has developed greatly in the past four years in China. Several in-situ experiments related with marine meteorology got much successful progresses carried by Chinese scientists, for example, the South China Sea Monsoon Experiment (SCSMEX), the South China Heavy Rain Experiment, Chinese First Investigation of Arctic, and the Comprehensive Survey of Nansha Islands and so on. These experiments enrich the data bank needed by marine meteorology research, and the results based on observational data are coming forth along with the experiments. In our review, a great proportion of papers belong to this class, which based on observational data.
In order to document the progresses of marine meteorology studies in China in the past four years conveniently, we divided these contents into six aspects actively in this paper. First aspect is observation and parameterization of air-sea flux. The main advances are air-sea flux observation in the South China Sea (SCS), the tropical Pacific and other oceanic regions, and improved parameterization of air-sea flux. Second aspect is sea ice, polar and high latitude marine meteorology. This includes the interannual and interdecadal variability of sea-ice in Arctic and Antarctic areas, sea-ice process and mechanism analysis in China seas and sea ice model validation. Third aspect is the marine meteorological disasters. The main points are climate dynamics associated to tropical cyclones in Northwest Pacific, tropical cyclones influencing China, the observation and simulation of typhoon storm surges and the prevention and reduction of marine disasters. Fourth aspect is the influence of sea surface temperature (SST) anomaly on weather and climate over China. The highlights are the relationship between weather and climate over China and SST in tropics, predictability signification of prophase SST, and so on. Fifth aspect is the interpretation to development of remote sensing research of marine meteorology. The key is the contribution of Chinese scholars to remote sensing of SST, sea surface wind field, and ocean wave. Sixth aspects is the content that reports the data analysis achievement of sea temperature analysis, data assimilation and its application.
II. OBSERVATION AND PARAMETERIZATION OF AIR-SEA FLUXES
Atmosphere circulation variability is driven directly by heat fluxes of the earth surface, so it is very important to describe heat fluxes of the earth surface exactly in atmospheric models. Sea surface is the widest underlying part to the earth, so much more attentions are paid to sea surface heat fluxes. In some key areas, such as the western Pacific warm pool, the eastern Pacific cool tongue, ITCZ and the trade wind zone, exact estimation of sea surface heat fluxes over these areas is very important. The changes of fluxes over these areas are regarded as the reasons of the ENSO evolution, of which the strongest climate signal in the earth.
Researches on air-sea fluxes of momentum, heat and moisture over the SCS develop rapidly in recent years. Now the local observation in the SCS is well developing. The SCSMEX and the scientific investigation in Nansha Islands in the Ninth Five-Year Plan, offer trustworthy data for studies on air-sea fluxes of momentum, heat and moisture in the SCS. Xu and Qu (2000) calculated the turbulent flux transfer during different weather conditions in winter 1997. The results show that all the momentum fluxes from atmosphere to ocean and sensible and latent heat fluxes from ocean to atmosphere during rainfall period are obviously greater than those during other weather periods. Wu et al. (2001) studied air-sea heat exchange under typhoon over the SCS. The main contribution to fluxes is from latent heat flux. When El Niño occurred, SST in the SCS became warmer, whereas air-sea heat exchange became weaker. Gao et al. (2000) calculated aerodynamic roughness length and neutral drag coefficient both on the smooth sea surface and rough sea surface over Nansha Islands in Sep. 1994. The relationship of aerodynamic roughness lengths, drag coefficients and bulk exchange coefficients with wind speed were also analyzed. Yan et al. (2000), detected turbulence structure and flux transfer at sea surface during the onset of the SCS monsoon in 1998. Intensities of turbulence are estimated. An expression of friction velocity was provided.
To certain degree, performance of modeling and prediction depends on the parameterization skill of air-sea fluxes in oceanic and atmospheric models. The study of influence of mesoscale enhancement on subgrid-scale sea surface fluxes of large-scale model by Zhang et al. (2001) indicated that the parameterization method of the mesoscale enhancement of sea surface fluxes must take the grid scale in the model into account. Zhao and Zheng (2000) noticed some problems in the computation of moisture and heat fluxes over surface for atmospheric models. They suggested a new flux-profile relationship formula, which is more reasonable theoretically, in which the effect of moisture on Monin-Obukhov parameter is considered, and a scalar roughness for virtual potential temperature is also introduced. Zhou et al. (2000) designed a coupled method in climate model to deal with air-sea fluxes exchange and successfully tested it by using the Global–Ocean–Atmosphere–Land system model developed at the State Key Laboratory of Atmospheric Sciences and Geophysical Fluid Dynamics (LASG) in Beijing.
Air-sea exchange is a critical process of air-sea interaction. Qian and Zhou (2001) analyzed temporal variations and geographical distributions of air-sea sensible and latent fluxes over the Pacific by using products from the Goddard Earth Observing System and four-dimensional Data Assimilation System. The results show that heat flux over the northwestern Pacific varies obviously with seasons, the value of sensible heat fluxes is often very small except over the ocean area north of 20°N and there is no highest value region at all. Regarding the impacts of SST diurnal cycle on the intraseasonal variation of surface heat flux over the western Pacific warm pool, Li et al. (2001) developed a parameterization scheme of diurnal cycle of SST. The compared examination are performed by integrations to National Center for Atmospheric Research (NCAR) Community Climate Model (CCM3), forced by observed weekly SSTs with and without diurnal cycle of SST, respectively.
III. MARINE METEOROLOGY IN POLAR AND HIGH LATITUDES
Sea ice, as an important component of the global climate system, affects atmospheric and oceanic circulations directly by interaction with airflows and currents. There exists notable correlation in different space scales and timescales between sea ice and atmosphere, sea ice and ocean, implying the importance of the ice-air-sea interaction in affecting climate on local areas, semi-global and even global scales. In polar region and high latitudes, ices and ocean, as the underlying surface of the atmosphere, play a dominant role in energy budget and hydrological cycle of the climate system. The high albedo of sea ice, decreasing the absorption energy of climate system, is the main cause resulting in polar region cooling.
Sea ice in China offshore has a significant interannual variability. The relationship between Bohai Sea, northern Yellow Sea ice and the climate change were investigated (Bai et al., 2001). The results suggest that the continuous diminishing sea ice in Bohai Sea in 1990s is coherent with the global warming trend. The interannual variation of the Bohai Sea and northern Yellow Sea ice status is relevant to El Niño phenomenon and the solar activity.
Several scientists addressed spatial and temporal evolution of sea ice in Arctic and Antarctic. The monthly and annual characteristics of the SST of the tropical western Pacific and Indian Ocean have been analyzed using COADS, together with their relation to ENSO and the Antarctic sea ice. It suggests that SST in the tropical western Pacific and Indian Ocean and Antarctic sea ice area has a close relation, and the outstanding correlation is that there is a 16-month SST lag for the Antarctic sea ice area (Chen and Qing, 2000). There exists an obvious interannual oscillation of sea ice in Arctic and Antarctic (Zhao et al. 2000). The Antarctic sea ice shows coherent characteristics of interannual variation in summer, whereas quite strong regional characteristics in autumn, winter and spring. The interannual anomalies of Arctic sea ice occur in different areas in cold seasons and warm seasons, respectively. Using 1953-1990 sea ice data sets, Wu et al. (1999) pointed that the variation of sea ice areas in Kara Sea, Barents Sea in winter may exert an influence on SST variability in the North Pacific in the following periods. Sea ice variability in Barents, Greenland, Baffin Bay, Davis Strait and Bering Sea in winter and spring is both interannual and interdecadal (Wu et al. 2000). The spring and winter sea ice in the Kara and Barents Seas presents out of phase with change in sea ice in the Bering Sea. Sea ice of Greenland, Kara and Barents Seas possesses significant 12 years period and 10 years variability, respectively. Wu et al. (2001) simulated the impact of the Arctic sea ice thickness and area on climate change of the East Asian regions using LASG two-level GCM. The results show that the variation of sea ice thickness can motivate propagation of planetary wave that span Eurasia, and also affect convection in the low latitude regions.
The relationship between Arctic sea ice and precipitation in North China areas was studied. It is disclosed the strong signal phenomenon of Arctic sea ice that appeared before climate variance on seasonal scales in China regions and the Northern Hemisphere. As such, the dynamics features of impact of the Arctic sea ice strong signal area on the drought in North China in summer are also analyzed (Bai 2000). As an important part of underlying surface, cryosphere is in the process of continuous interaction with atmosphere. It is shown that the Arctic sea-ice strong signal region is highly correlated with the summer precipitation in North China. The mechanism how the Arctic sea-ice would affect North hemisphere summer circulation and the flood-drought in North China is put forward, namely how the Arctic strong signal region may affect the abnormal precipitation of North China is put forward.
Numerical modeling is a powerful tool to insight the dynamics associated to sea ice. Liu et al. (2000) improved the ice-ocean thermal coupled scheme, applied in a global ice-ocean coupled model. One-dimension sea ice thermal model can reflect better the sea ice variation trend in vertical direction, but it can't embody the sea ice condensation increasing velocity better (Zhang et al. 2000).
IV. MARINE METEOROLOGICAL DISASTERS
The marine meteorological disasters are generally included by tropical cyclones (typhoon), marine gale, marine fog, marine severe convective storm, storm surge, sea ice, sea waves, tsunami and so on. They mainly threaten sea surface and coastal belt; some of them endanger the safety of the economy and demos life property from seashore to inland large region. All of them generally have the background of marine environmental calamity caused by severe weather system. Because of difficulties of in-situ measurement, the mechanism of marine meteorological disaster has not been studied fully and this makes marine meteorological disasters an austere challenge in reducing and preventing the general disasters.
The Northwest Pacific is the most frequent and strongest region of global tropical storm activity and China is one of the most serious countries affected by typhoon along the seashore of Northwest Pacific. 80-100 tropical cyclones occur every year globally and they have a great impact on human life. The loss caused by tropical cyclones is the severest and accounts for the 64 percent of the death caused by all natural disasters. According to the statistics, 15-20 thousand persons died in the calamity of tropical cyclones and the global economical loss adds up to 60-70 hundred million dollars annually.
The response of ocean to typhoon process has not been so well monitored due to high expenses. People have another option, that is, to simulate or predict by models. Using a numerical model, Su et al. (2001) quantitatively analyzed the factors that can cause SST change during typhoon process in the Yellow Sea and Bohai Sea. The rate of SST change caused by different factors in the typhoon center and its adjacent points were given as well. Yang (2001) examined the degree of disasters (disaster classification, disaster frequency, occurrence over return period) caused by typhoon landfall along the huge coastal line from the Bay of Bohai Sea to Guangxi, South China, and points the possibility addressing the destruction of strong typhoon using Poisson distribution. Xie et al. (2001) had studied the diagnostic model of typhoon surface wind in the coastal and estuary regions. The large domain wind field and the initial wind field of the mesoscale dynamic diagnostic model were obtained through nesting the typhoon model with that of the NCAR objective analysis. At the same time, through a nudging assimilation scheme combined with real data to rectify the diagnostic wind field, one may obtain sea surface wind fields in these regions. Gao et al. (2001) had tested the 24-hour prediction of sea surface winds in the Bohai Sea with the initial field provided by objective analysis of T106 model grid data and the observation data in the upper air and the ground layer, as well time-variable boundary condition provided by T106 model every 6 hours.
The characteristics of cyclones over sea are of quick development and difficult prediction. Qian et al. (2001) had objectively classified the disaster grade to manifest the destruction degrees. In order to validate the method, evaluation by the independent Suffir-Simpson data of tropical cyclone disasters is also done. Lin and Zhan (2000) had analyzed the impact of SST in the equatorial eastern Pacific on extratropical cyclone, say, East Asia and Northwest Pacific. The corresponding relation is preferential that strong extratropical cyclone is excessive in the El Niño year or following year. But when the subtropical high is slightly higher than normal, the extratropical cyclones are less. Zhang et al. (2000) tested the dynamical reason of abrupt cyclones in winter and found that the occurrence and development of abrupt cyclones are due to the southern invasion of abnormal vortex strength below the stratosphere and downward propagation of perturbation in the troposphere and cold air above.
Storm surge is one of marine dynamical disasters and has great destruction. Several studies demonstrate the important role of an enforced and accurate prediction of disaster to reduce and prevent marine disasters. Yu et al. (2000) developed a numerical model for extratropical storm surge with a spherical coordinate. Simulation shows that the numerical modeling of extratropical surge is practical as long as forcing wind is accurate. The simulation by Wang et al. (2001) shows that the computation domain of the sea will seriously affect the modeled process of storm surge in an enclosed or semi-enclosed sea and a satisfactory result will be obtained only when the calculation field covers the Bohai and Yellow Seas. Using a two-dimensional barotropic shallow water model and nesting computation skill, Zhao et al. (2000) simulated storm surge of 20 consecutive years for Chengbei and the adjacent areas and had done the long-term predication of return period set-up values caused by storm surge. Zhou and Sun (2000) simulated storm surge caused jointly by Typhoon 8114 and astronomical tide using a 2-dimensional numerical model to study the nonlinear interaction between storm surges and astronomical tides in the sea area off the Yangtze River mouth. Li et al. (2000) introduced the disaster outline of southern Fujian Province caused by Typhoon 9914, and analyzed the characteristics of typhoon and storm surge there.
Sea fog is another marine meteorological phenomenon affecting sea activity greatly. Xie et al. (2001) found that various kinds of sea fogs can be formed, such as advection fog, radiation fog and evaporation fog in the Arctic, most of which is covered with ice or is mixed with ice. The reason why there are many kinds of fog types in the Arctic Ocean is the complicated cushion and consequent air-sea interaction caused by sea ice distribution and its unique physical characteristics. Using the East Asian daily 08Z surface synoptic charts from 1980-1997, Li and Wang (2000) had induced and analyzed 4 kinds of synoptic patterns that can form fog in Taiwan strait region (20°-27°N, 115°-125°E). They are cold advection prevailing pattern, warm advection prevailing pattern, homogeneous pressure field pattern and typhoon outer region pattern, respectively.
V. INFLUENCE OF OCEAN ON WEATHER AND CLIMATE OVER CHINA
As early as 1950, Chinese scientists have noticed the relationship between the northwest Pacific SSTA and consequent drought and flood in the Yangtze River. After that, many people dedicated themselves to search for sea areas of previous SSTA, which are closely connected with climate in China, including spring equatorial cool water zone, Arabian Sea, Indian Ocean, the SCS, Kuroshio, the warm pool in West Pacific, the equatorial eastern Pacific etc. Recently, a lot of authors related SST or sea ice with anomalous atmospheric circulation and achieved the atmospheric teleconnection wavetrain, which is connected with SSTA preceding Chinese summer climate anomaly. Thus they disclosed the detailed processes that preceding SSTA affects Chinese climate anomaly by way of affecting atmospheric circulation. It was pointed out that SSTA in the western Pacific warm pool would cause a teleconnection wavetrain and further influence summer rainfall in the middle and lower reaches of Yangtze River. Atmospheric circulation anomaly caused by spread of quasi-constant planet wave will cause atmospheric circulation anomaly in other areas.
There is rather complex relationship between summer precipitation over China and SST in the Pacific. Using 50-year observations data, Ge (2000) diagnosed summer precipitation in China and SST in the Pacific and discovered that both characterize a decadal variability. Sensitivity numerical experiments were carried when sea temperature in the Pacific is of warm background. Chen (2000) examined the summer drought/flood in China under condition of winter-strengthening pattern and winter-weakening pattern of El Niño and La Niña. A physics concept pattern is proposed to interpret the summer rainfall patterns over China, associated with different patterns of El Niño and La Niña in winter. Lin and He (2000) investigated the relationship between the Pacific SSTA pattern and the East Asian atmosphere circulation and rainfall in the middle and lower reaches of Yangtze River. The numerical experiments further confirm that rainfall in the middle and lower reaches of the Yangtze River is not only related to SSTA in the tropics but also to that in the mid-latitude Pacific. Li and Shou (2000) considered that the eastern equatorial Pacific temperature is the factor of summer drought/flood in the Huaihe River. The summer precipitation over the Yangtze and Yellow River Basins is greater than normal when El Niño warming occurs in autumn or winter, whereas, less when ENSO develops in spring or summer. High correlation between preceding and simultaneous SST in the northern Pacific and spring rainfall in northwestern China is detected objectively (Wang et al. 2001). Such forecast significance of the high correlation areas is discussed. Sun et al, 2000 suggested an index of land-sea thermal difference (ILSTD). The index reflects the interannual variation of summer rainfall anomaly over eastern China, especially in Northeast China, and the Huaihe Valley and mid/low reaches of the Yangtze River. In the years of strong ILSTD, rainfall belt mainly locates over the north part of China, and obvious drought emerges in the Huaihe Valleys and mid/low reaches of the Yangtze River. Zhu et al. (2000) investigated the barotropic and baroclinic components of 850hPa u field to look for a possible mechanism of effects of SSTA in the preceding March over (42.5°-52.5°N, 170°E-170°W) on summer rainfall in the East China. Results show that SSTA in March has effects on 850 hPa baroclinic wavetrain of the same season. The baroclinic wavetrain in March can affect the baroclinic wavetrain in summer, which at last can change the summer rainfall in East China.
Chinese scientists also noticed the possible impact on East Asian climate from other ocean, for example, the Atlantic Ocean. Meiyu onset dates (MOD) are significantly related to the atmospheric features in the previous winter. With strong North Atlantic Oscillation, the Meiyu onsets early (Xu and He, 2001). There exists pronounced correlation between the MOD and SST over the North Atlantic in the previous winter-to-spring with positive SST anomalies for early Meiyu onset and negative anomalies for late Meiyu onset.
Impacts of SSTA in Indian Ocean on weather and climate in China were greatly attracted since the Indian Dipole has been reported. The numerical simulation experiments show that SSTA in Indian Ocean poses a significant influence on the distribution of precipitation anomalies in China during El Niño. Yan and Xiao (2000) indicated that the warmer (colder) SSTA in the equatorial Indian Ocean would result in a wavetrain, which is similar to the teleconnection patterns PNA and EAP in middle and high latitude regions. With the warmer (colder) SSTA forcing, Asian summer monsoon will burst later (earlier) and withdraw earlier (later) than normal, and it will last shorter (longer) and its intensity is weaker (stronger) than normal. Li and Ding (2002) found negative correlation exists between summer rainfall in North China and SSTA in Indian Ocean areas, which is close to east coastal of Africa. The SSTA pattern with warm west and clod east SST in Indian Ocean will make Indo-China drier and reduces precipitation over the northern China, but increases precipitation over the area in Southwest China and South China (Xiao et al. 2000).
Sea areas which affect East Asian weather and climate are various with interannual variability of ocean-atmosphere system. Several studies checked out the relationship between atmosphere circulation in East Asia and SST in the SCS and its vicinity. Gao et al. (2000) classified the features of atmospheric circulation and SST with reference to anomalous occurrence of tropical cyclones in Fujian during 1951-1996. Mao et al. (2000) reported that SST over the SCS, Pacific and Indian Oceans and their variations could all influence the onset of summer monsoon over the SCS. Wang et al. (2001) did experiments for regional atmospheric circulation's response to SST anomalies in SCS. When there are cold SST anomalies in the SCS and the Bay of Bengal and warm anomalies in the western tropical Pacific Ocean, there is anomalous northeasterly over the SCS in February and March. Moreover, there is anomalous anticyclonic circulation (AAC) generated over Philippine in summer. The AAC low frequency variability results in a coherent low activity in the East Asian atmospheric circulation by way of teleconnection. Ren and Qian (2000) found that there are apparent negative correlation between latent heat flux over the northern SCS in the preceding winter and the same summer precipitation in South China and its coastal regions. In spring a strong positive correlation between latent heat flux over the middle SCS and the precipitation in the area from the south of the Yangtze River to South China coastal regions is found. Qian and Chen (2001) searched for the relationship between monsoon intensity and sea level anomalies for the Pearl River mouth around the occurrence of El Niño in the past 45 years. The results show that the wind mean speed is larger than normal in the preceding winter and monthly mean speed is generally higher than normal in the current year of El Niño events, while the monthly mean sea level is lower than normal.
VI. REMOTE SENSING IN MARINE METEOROLOGY
The physical oceanographic phenomena with basin scales have been concerned highly. But the investigated region at present is just only a part of the whole ocean, so all of the knowledge on these events has not revealed well yet. In conventional oceanographic surveys, which were influenced by many factors, especially by limited money, the vast sea area could not be explored entirely at the same time. Therefore, the remote sensing of oceanic meteorology has more powerful superiority to explore such vast area than the conventional survey.
Microwave remote sensing applied in marine meteorology provides accurate retrieval for sea surface wind and ocean wave. He (2000) discussed the possibility to measure ocean current and bottom topography, and provided the method to detect ocean wave, sea surface wind, surface current, bottom topography, and internal wave, by using the microwave scatter principles over sea and SAR missions. Wang Jin and Qi et al. (2001) found the spatial and temporal features of wind and wave fields in the SCS, by using EOF to analysis sea surface wind and wave fields deduced by TOPEX/Poseidon space-based altimeter data. The result showed the relationship between wind field and wave field in the SCS. Xie et al. (2001) found that the remote sensing data have finer resolution and more reasonable values, by using remote sensing (ERS1 and ERS2) data, COADS data and Hellerman & Rosenstin objective analysis data to analyze sea surface stress in the SCS. Therefore they suggested choosing remote sensing data in the study of climatologic feature of distribution of wind stress and its seasonal variability in the SCS, especially in the studies of small and middle scale eddies. Analyzing the remote sensing data by Geosat altimeter between 1987 and 1988, Qi and Shi (1999) indicated distribution of monthly sea surface wind speed and valid wave height in the SCS, and the annual cycle of wind and wave fields along NE-WS direction. In this paper, it is compared with wind and wave based on buoy data. Jiang and Sun (2000) studied the microwave radiate theory primarily, basing on in situ measurement by microwave radiation and data procession. Meanwhile, the relationship was showed among kinds of conditional and radiometer parameter and the microwave spectrum over sea. Fang and Chen (2001) developed a marine geographical information system (MGIS) for predicting global extreme sea surface wind speeds. It can be used to model the global wind system, estimate its extreme values and visualize the predicted results. The significance of global extreme wind speed estimate and the importance of using MGIS in the analysis process are discussed. A statistical model for estimating global extreme sea surface wind speed is proposed.
Sea surface wind vector can be measured by imaging radar onboard space aircrafts. The SAR images in April 1994, taken from imaging radar on aircraft over the SCS, were analyzed by Wang and Pan (2000). The wind direction is taken from SAR image spectrum by using SIR-C data. And the wind speed is retrieved from the C-band radar backscatter by using CMOD4 model.
SST derived from the infrared remote sensing observation not only provides thermal situation of ocean, but also implies information of oceanic currents. Xu (2001) revealed the oceanic phenomena over the South Chin Sea, by using the NOAA AVHRR images cover the South China Sea in the period of 1989-1993 and in situ measurement CTD data over the northeastern SCS in March 1992. The distribution of SSTs derived from satellite images are almost coincided with the in situ measurement. The retrieved method of orbiting meteorological and operational satellite product SST and its accuracy verified was represented by Wang (2001) using the data based on ship in each month of four seasons in 1996 to verify the accuracy of SST. The mean difference is –0.6℃, the root-mean-square difference is 1.5℃. The difference between the PESST and in-situ data in East China Sea (Gao et al., 2001) showed that the PESST data are coincided with in-situ measurement. 67.6% of all analyzed data difference is inferior to or equal to 0.5℃, and the root-mean-square difference is 0.61.
Remote sensing analysis of dynamic oceanic processing: Liu et al. analyzed the tides deduced from TOPEX/Poseidon altimeter data over the SCS by using the comparing difference method. The synthetic geostrophic current fields are derived from the mean sea level and sea level height anomalous. It's found that the surface geostrophic current in the SCS is cyclonic generally. The westerly surface current in autumn and winter is enhanced obviously. He et al. found that the trajectories of four Agros drifting buoys over the SCS fit the trends of oceanic basin's circulation in each season, and become middle scale in west of Philippine, outer sea of Vietnam, and central part of the SCS, respectively. These middle scale vortexes are validated accurately by the sea level height anomalous from TOPEX remote sensing at the same time. Ji et al. (2002) suggested one method to examine the middle scale vortexes from remote sensing images over sea. The results showed that the mature vortexes, which have obvious feature in shape, are inspected.
VII. NEW METHODOLOGY IN MARINE METEOROLOGY
Any step of methodology progress in marine meteorology will lead to successful advances about experimental and operational application. Recently oceanic prediction attracts much attention with revolution in data collect and great improvements about data assimilation in atmospheric and oceanic models.
Theoretical studies on data assimilation in marine meteorology provided a reasonable fundament for us to adopt the new techniques in this field. As a sample, the derivations of the First Order Adjoint (FOA) and Second Order Adjoint (SOA) models of the shallow water equations are given in detail by Han et al. (2000), where they obtained the Hesse matrix of the SOA, which improves a previous SOA theory. In order to provide more accurate initial field for numerical predict of SST, the adjoint method was applied by Han (2000b) to assimilate sea temperature observations into one-dimensional model. By a method of discrete adjoint operator in data assimilation for prediction of the vertical distribution of temperature, He et al. (2000) got an accurate initial temperature field for numerical prediction. Wang et al. (2000) carried out an objective analysis method, which can be used to improve oceanic observation scheme optimally depending on variational data assimilation.
Prospects of marine prediction seem exciting due to much applications of data assimilation in marine meteorology. Prediction of annual occurrence of tropical cyclones using the products of a hybrid air-sea coupled model was done by Li et al. (2000) by applying a four-dimensional variational assimilation system regarding optimization of the initial field for the predicting integration. Thus, the prediction accuracy of interannual SSTA in the tropics was improved. Duan et al. (2000) applied the four-dimensional variational data assimilation system of the Zebiak-Cane model to predict ENSO. Comparing with the observational result, the forecasting results derived from this assimilation system in which the fields of January 1997 are reproduced, agree well with it. In assimilation experiment of blending TPOEX altimeter data in the SCS, Wang et al. (2001) compared the control run result without assimilation and that with the assimilating run. They found out that blending TOPEX altimeter data could modify reasonably the large-scale circulation in the SCS, such as the dynamic process relevant to the impact on the northeastern SCS caused by intrusion of Kuroshio. Lu (2001) applied a variational optimal technique on assimilating both meteorological and oceanographic (surface and currents) observations into an oceanic Ekman Layer model, through which the unknown condition (such as, the wind stress drag coefficient) and the unknown vertical eddy viscosity are deduced simultaneously by this method. Chen (2001) used Princeton Ocean Model to assimilate observation data (including AXBT and MCSST derived from satellites) in the SCS in May 1995. Result showed that the simulated temperature and current field were improved much. In order to improve prediction of tidal information in the continental shelf, Han et al. (2001) used a variational assimilation method in the Yellow Sea and East China Sea by incorporat ing the data from tide stations with/without TOPEX/Poseidon altimeter data.
In the past four years we saw that several new techniques for sea temperature analysis and forecasting were proposed in China, which have an insight for further application in marine meteorology. Wei et al. (2001) provide a method to detect the embedded frequencies in chaotic system to analyze ocean data. They detected the embedded periods of the equatorial daily SST time series and the nine points running mean monthly air temperature of Qingdao, using the frequencies spectrum and the probability of points in a reconstructed phase space. Application of a localized nonlinear direct forecasting method to detect ocean chaos and noise (Wei et al. 2000) gave evidence that this method is better than a kind of general spectral analysis in detecting chaos and noise in SST time series. In regressive filter objective analysis of SST fields, undergone by Wang et al. (2000), the regressive filter is used to deal with scale-varying and heterogeneous SST data. By adjusting several key parameters, they obtain the SST fields at a fine resolution. Using a nature oscillator equation, Cao et al. (2000) obtained an inversed time-lag nature-oscillator equation, which can describe the quasi-nonlinear feature of SST evolution in the eastern tropical Pacific. Jiang and Wu (2001) detected TOGA-TAO SST data of the 53 buoy moored in the tropical Pacific in winter 1994 to know whether there exist the ocean chaotic characteristics in the tropical Pacific. It is found that the underlying system of the eastern and western Pacific is always chaotic, but the reason for the chaos present in the two regions may be different. Ren and Zhou (2001) applied an analogue model, which is suitable for doing similarity forecast for a time series, to Nino3 SST anomaly, an important index for ENSO monitoring. The maximum leading period of effective prediction is 8 months, and the similarity forecast has quite good ability for the turn-point events.
Known from the above, a large number of papers have been published in the past four years by Chinese oceanographic and meteorological community in marine meteorology studies. These great efforts were made over several aspects, for example, air-sea flux, marine meteorology in high latitudes, marine disasters, connection between ocean and weather/climate in China, relevant remote sensing application, as well as new methodology in this field. We should aim at the international development tendency of meteorology, and probe into the predominance development domain of marine meteorology of China in the latter period.
Acknowledgement: The authors would like to thank our colleagues Mr./Ms. GU Dejun, LIU Chunxia, LI Chunhui, BI Xueyan, CHEN Ju, LIU Qinyan, and LI Haiyang for their kind help.
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