南海海—气通量交换研究进展

1998年的“南海季风试验(SCSMEX)”已经过去10年了,SCSMEX启动的南海海—气通量试验研究也有10个年头。在SCSMEX和国家自然科学基金面上项目“南海季风爆发期近海面层通量观测和湍流结构的观测研究”支持下,10年来在西沙实施了3次(1998年、2000年、2002年)海—气通量观测试验,开展了试验资料分析研究,重点是西南季风爆发前后海—气通量交换过程研究,辐射通量、感热通量、潜热通量、动量通量随天气条件的变化研究,海—气通量日变化,通量交换系数以及通量变化对低层大气、上层海洋的影响研究。对10年来南海通量研究作一回顾,对未来的通量观测研究计划特别是2008“亚洲季风年”西沙通量观测提出一些建议。

东海海—气界面二氧化碳通量的季节变化与控制因素研究进展

通过对东海海—气界面二氧化碳(CO2)交换有关研究的总结,剖析了东海表层海水CO2分压(pCO2)的区域分布特征,探讨了海—气界面CO2通量(FCO2)的季节变化规律,诠释了影响海—气界面CO2转移的主要因素。结果表明,东海表层海水pCO2的区域分布具有明显的季节变化,可将其分为冬季、夏季、过渡季节(春季、秋季)3个时段。冬季西部近岸海域由于水体垂直交换强烈,造成表层水体pCO2较高,而中、东部陆架海域由于浮游生物的光合作用使得pCO2较低。夏季近岸河口海域由于陆源输入的影响导致pCO2较高,中、东部陆架海域受温跃层、长江冲淡水、浮游植物的综合作用pCO2较低。春季、秋季为过渡时段,表层海水pCO2分布变化剧烈,受控因素较为复杂。东海全年表现为大气CO2的净汇,其中冬、春、夏为碳汇,其海—气界面FCO2分别为(-6.68±6.93),(-4.94±0.80),(-3.67±1.09)mmol/(m2·d)。秋季表现为碳源,通量约为(1.50±8.37)mmol/(m2·d)。东海全年平均通量约为-3.16 mmol/(m2·d),共可吸收CO2约为6.92×106t C/a。不同季节海—气界面FCO2的年际变化凸显了人为因素的影响,近海富营养化加剧,三峡工程的运行都可能是造成东海冬季碳汇量减少、秋季碳源/汇格局转变的原因。

Sea Surface Temperature Simulation of Tropical and North Pacific Basins Using a Hybrid Coordinate Ocean Model (HYCOM)

A Hybrid Coordinate Ocean Model （HYCOM） is used to simulate the sea surface temperature of the Tropical and North Pacific. Based on the different combinations of two air-Sea flux data sets （COADS and ECMWF） and two bulk parameter formulas （non-constant and constant）, four numerical experiments are carried out. The following conclusions can be deduced from the numerical results. （1） The numerical results using non-constant bulk parameter formula are much better than those using constant one. In the Pacific area from 40°N to 20°S, the annual average SST obtained from the experiment using non-constant bulk parameter formula is 0.21 ℃ higher than that from the satellite-based SST climatology （the pathfinder data）. However, the difference is 0.63 ℃ for the experiment when the using constant one. （2） HYCOM successfully simulates the monthly variation of climatological SST in tropical and north Pacific basins and monthly spatial variation of Western Pacific Warm Pool. Especially in the Pacific area from 40°N to 20°S, the difference of the seasonal averaged SST between pathfinder data and the result of experiment 2 （using COADS data set and non-constant bulk parameter formula） is only about 0.02 ℃. （3）The simulation results using different Air-Sea flux data are different and the difference is very large in some regions. In the northwest of the model region, the annual average SST obtained from experiment 2 （using COADS data set） is 1℃ higher than that obtained from experiment 4 （using ECMWF data set）. Contrarily, the result of experiment 4 is 1 ℃ larger than that of experiment 2 in the southeast of the model region. The largest difference is about 4 ℃ occurred near the area of 58°N, 140°E and the Bohai sea.

冬季和夏季长江口及其邻近海域一氧化碳的分布、海-气通量和微生物消耗的研究

海洋是大气中一氧化碳(CO)的重要来源,河口区域在调节气候活性气体收支方面发挥着重要作用。本文旨在研究长江口作为典型河口在全球海洋CO生物地球化学循环中的地位,并进一步了解河口区域海水和大气中CO浓度的变化情况。本文基于2021年冬季和夏季在长江口及其邻近海域的现场调查,对该海域CO分布、海-气通量和微生物消耗速率进行了研究。结果表明,冬季和夏季调查海域大气中CO的体积分数平均值分别为(530.39±120.40)×10^(-9)和(416.91±102.01)×10^(-9),大气中CO含量受人类活动影响较大;受光照强度和陆源输入有机物的影响,夏季表层海水中CO的浓度平均值[(4.52±2.13)nmol/L]显著高于冬季[(1.30±0.79)nmol/L];相应地,夏季海—气通量平均值[0.95μmol/(m^(2)·d)]亦显著高于冬季[0.10μmol/(m^(2)·d)]。冬季的微生物消耗速率常数(kbio)的平均值[(0.46±0.31)/h]明显高于夏季[(0.26±0.07)/h],其空间分布差异不大。本文的研究结果有助于深入认识河口区域在全球海洋CO生物地球化学循环中的地位。

Assessment of surface drag coefficient parametrizations based on observations and simulations using the Weather Research and Forecasting model

The drag coefficient is important in meteorological studies of the boundary layer because it describes the air-sea momentum flux. Eight drag coefficient schemes were assessed. These parametrizations were compared taking into account data from in situ and laboratory observations.The drag coefficients determined using three schemes were consistent with the level-off phenomenon, supported by the results of laboratory studies. The drag coefficient determined using one scheme decreased at wind speeds higher than approximately 30 m s-1, in agreement with indirect measurements under typhoon conditions. In contrast, the drag coefficients determined using the other four schemes increased with wind speed, even under high wind regimes. Sensitivity tests were performed using simulations of two super typhoons in the Weather Research and Forecasting model. While the typhoon tracks were negligibly sensitive to the parametrization used, the typhoon intensities （the maximum lO-m wind speed and the minimum sea level pressure）, sizes, and structure, were very sensitive to it.

Analysis of atmospheric turbulence in the upper layers of sea fog

Atmospheric turbulence plays a vital role in the formation and dissipation of fog. However,studies of such turbulence are typically limited to observations with ultrasonic anemometers less than 100 m above ground. Thus,the turbulence characteristics of upper fog layers are poorly known. In this paper,we present 4-layers of data,measured by ultrasonic anemometers on a wind tower about 400 m above the sea surface; we use these data to characterize atmospheric turbulence atop a heavy sea fog. Large differences in turbulence during the sea fog episode were recorded. Results showed that the kinetic energy,momentum flux,and sensible heat flux of turbulence increased rapidly during the onset of fog. After onset,high turbulence was observed within the uppermost fog layer. As long as this turbulence did not exceed a critical threshold,it was crucial to enhancing the cooling rate,and maintaining the fog. Vertical momentum flux and sensible heat flux generated by this turbulence weakened wind speed and decreased air temperature during the fog. Towards the end of the fog episode,the vertical distribution of sensible heat flux reversed,contributing to a downward momentum flux in all upper layers. Spatial and temporal scales of the turbulence eddy were greater before and after the fog,than during the fog episode. Turbulence energy was greatest in upper levels,around 430 m and 450 m above mean sea level(AMSL),than in lower levels of the fog(390 m and 410 m AMSL); turbulence energy peaked along the mean wind direction. Our results show that the status of turbulence was complicated within the fog; turbulence caused fluxes of momentum and sensible heat atop the fog layer,affecting the underlying fog by decreasing or increasing average wind speed,as well as promoting or demoting air temperature stratification.

Interannual salinity variability of the Northern Yellow Sea Cold Water Mass

This paper discusses the interannual variability of the Northern Yellow Sea Cold Water Mass(NYSCWM) and the factors that influence it,based on survey data from the 1976–2006 national standard section and the Korea Oceanographic Data Center,monthly E-P flux data from the European Centre for Medium-Range Weather Forecasts,and meridional wind speed data from the International Comprehensive Ocean-Atmosphere Data Set. The results show that:1) the mean salinity of the NYSCWM center has a slightly decreasing trend,which is not consistent with the high salinity center; 2) both the southern salinity front and the halocline of the NYSCWM display a weakening trend,which indicates that the difference between the NYSCWM and coastal water decreases; 3) the Yellow Sea Warm Current intrusion,the E-P flux of the northern Yellow Sea,and the strength of the winter monsoon will affect the NYSCWM salinity during the following summer.

Indian Ocean SST Biases in a Flexible Regional Ocean Atmosphere Land System(FROALS) Model

The authors examine the Indian Ocean sea surface temperature(SST) biases simulated by a Flexible Regional Ocean Atmosphere Land System(FROALS) model.The regional coupled model exhibits pronounced cold SST biases in a large portion of the Indian Ocean warm pool.Negative biases in the net surface heat fluxes are evident in the model,leading to the cold biases of the SST.Further analysis indicates that the negative biases in the net surface heat fluxes are mainly contributed by the biases of sensible heat and latent heat flux.Near-surface meteorological variables that could contribute to the SST biases are also examined.It is found that the biases of sensible heat and latent heat flux are caused by the colder and dryer near-surface air in the model.

Air-sea fluxes of heat and momentum over the Yellow Sea during cold air outbreaks

The impact of sea surface waves on air-sea fluxes of heat and momentum over the Yellow Sea caused by cold fronts during cold air outbreak(CAO)events is investigated through numerical experiments with a FVCOM-SWAVE(Finite-Volume Coastal Ocean Model-Surface WAVE)wave-current coupled model.Two typical types of cold fronts,i.e.,those respectively from the north and from the west,are simulated and compared to each other and with monthly mean.During cold seasons,currents in the Yellow Sea are weaker than that during warm seasons.As a result,waves show a more prominent impact.The numerical simulations suggested that both the heat and momentum fluxes are significantly enhanced during CAO events;and they could be a few times larger than the monthly average of a five-year mean.The enhancement is highly sensitive to the features of CAOs.Specifically,it depends on the cold front orientation,intensity and evolution.One mechanism that strengthens the two fluxes is via sea waves.For the CAOs that are studied,an increase in sea wave height by 50%can double the maximal momentum flux,and cause an increase in heat flux by 10-160 W/m^2.

SURFACE OBSERVATIONS IN THE TROPICAL CYCLONE ENVIRONMENT OVER THE SOUTH CHINA SEA

In this paper, the observational data from Marine and Meteorological Observation Platform （MMOP） at Bohe, Maoming and buoys located in Shanwei and Maoming are used to study the characteristics of air-sea temperature and specific humidity difference and the relationship between wind and wave with the tropical cyclones over the South China Sea （SCS）. The heat and momentum fluxes from eddy covariance measurement （EC） are compared with these fluxes calculated by the COARE 3.0 algorithm for Typhoon Koppu. The results show that at the developing and weakening stages of Koppu, both these differences between the sea surface and the near-surface atmosphere from the MMOP are negative, and data from the buoys also indicate that the differences are negative between the sea surface and near-surface atmosphere on the right rear portion of tropical cyclones （TCs） Molave and Chanthu. However, the differences are positive on the left fi＇ont portion of Molave and Chanthu. These positive differences suggest that the heat flux is transferred from the ocean to the atmosphere, thus intensifying and maintaining the two TCs. The negative differences indicate that the ocean removes heat fluxes from the atmosphere, thus weakening the TCs. The wind-wave curves of TCs Molave and Chanthu show that significant wave height increases linearly with 2-min wind speed at 10-m height when the wind speed is less than 25 m/s, but when the wind speed is greater than 25 m/s, the significant wave height increases slightly with the wind speed. By comparing the observed sensible heat, latent heat, and friction velocity from EC with these variables from COARE 3.0 algorithm, a great bias between the observed and calculated sensible heat and latent heat fluxes is revealed, and the observed friction velocity is found to be almost the same as the calculated friction velocity.

NUMERICAL EXPERIMENTS ON THE IMPACTS OF SEA SPRAY ON TROPICAL CYCLONES

The latest version of sea spray flux parameterization scheme developed by Andreas is coupled with the PSU/NCAR model MM5 in this paper. A western Pacific tropical cyclone named Nabi in 2005 is simulated using this coupled air-sea spray modeling system to study the impacts of sea spray evaporation on the evolution of tropical cyclones. The results demonstrate that sea spray can lead to a significant increase of heat fluxes in the air-sea interface, especially the latent heat flux, the maximum of which can increase by up to about 35% - 80% The latent heat flux seems to be more important than the sensible heat flux for the evolution of tropical cyclones. Regardless of whether sea spray fluxes have been considered, the model can always simulate the track of Nabi well, which seems to indicate that sea spray has little impact on the movement of tropical cyclones. However, with sea spray fluxes taken into account in the model, the intensity of a simulated tropical cyclone can have significant increase. Due to the enhancement of water vapor and heat from the sea surface to the air caused by sea spray, the warm core structure is better-defined, the minimum sea level pressure decreases and the vertical speed is stronger around the eye in the experiments, which is propitious to the development and evolution of tropical cyclones.

Relations between Low-Frequency Modes of Climate Variability and Air-Sea Heat Flux at the Mediterranean Interface

The main objective of this work is to examine statistical causality relationships between low-frequency modes of climate variability and winter （December to February） anomaly of net heat flux at the Mediterranean air-sea interface. The introduction of the concept of Granger causality allowed us to examine the influence of these climates indices on the net heat flux anomaly and to select Mediterranean surface regions that really influenced by each index. Results show that the winter anomaly of the net heat flux in the Algerian basin south and the gulf of Lion is mainly caused by the Arctic Oscillation. El Nifio-Southern Oscillation influences much more the Algerian basin north and the northern lonian Sea. The Quasi-Biennial Oscillation affects only the Alboran and the Tyrrhenian Seas. But the Adriatic and Levantine basin are impacted by any climate index. They also show that these climate indices can increase explained variance in winter variations of air-sea net heat flux by 10% to 15%, with a lag of three seasons. These relationships are less persistent and spatially limited.

Air-Sea Exchange of Volatile Organic Compounds: A New Model with Microlayer Effects

The authors propose a new "three-layer" conceptual model for the air-sea exchange of organic gases, which includes a dynamic surface microlayer with photochemical and biological processes. A parameterization of this three-layer model is presented, which was used to calculate the air-sea fluxes of acetone over the Pacific Ocean. The air-sea fluxes of acetone calculated by the three-layer model are in the same direction but possess half the magnitude of the fluxes calculated by the traditional two-layer model in the absence of photochemical and biological processes. However, photochemical and biological processes impacting acetone in the microlayer can greatly vary the calculated fluxes in the three-layer model, even reversing their direction under favorable conditions. Our model may help explain the discrepancies between measured and calculated acetone fluxes in previous studies. More measurements are needed to validate our conceptual model and provide constraints on the model parameters.

南海碳源汇的区域与季节变化特征及控制因素研究进展

南海碳循环是全球碳循环的重要组成部分。厘清南海CO2通量问题,对阐明全球碳循环过程,完善全球碳循环数据库具有重要意义。对南海4个典型特征区域(北部陆架、北部陆坡及海盆、吕宋海峡西侧海域和中南部海盆)的海表CO2分压、CO2通量和控制因素的研究进展进行了归纳总结。结果显示,南海北部陆架海表CO2分压区域差异显著,珠江冲淡水上游低盐区为强碳源,海表CO2分压常年处于超饱和状态,最高值达405.3~810.6 Pa,下游离岸开阔海域(盐度大于33.7)冬季海表CO2分压低至35.2~37.0 Pa,为弱的碳汇。南海北部陆坡、海盆受温度调控,暖季是碳源,冷季是碳汇,夏季海表CO2分压最高达45.0 Pa,冬季海表CO2分压最低为34.7 Pa。吕宋海峡西侧海域碳源/汇受温度、季风和水团等因素影响较大,春季海表CO2分压与大气CO2分压接近于平衡状态,冬季升高至38.4~47.5 Pa,高于大气CO2分压。中南部海盆表现为大气CO2弱或中等强度的源,海表CO2分压年均值为41.0 Pa。总体上,南海大部分海域在全年尺度上表现为弱的碳源,每年向大气释放(18±10)Tg C的CO2。虽然南海碳循环研究已取得了一定进展,但仍缺少长期的现场观测与数据积累。今后应进一步加强海—气CO2分压时间序列研究和海—气CO2交换通量的遥感研究。