Total energy equation method for calculating hurricane intensity

Summary Surface pressure reduction in hurricanes is calculated by applying the total energy equation (TEE) to ideal isentropic upflow in a vertical tube. The pressure reduction at the base of the tube, called the intensity, is calculated for three upflow processes: reversible upflow of air approaching equilibrium with the sea at the sea level pressure outside the tube; irreversible upflow of air approaching equilibrium with the sea at the sea-level pressure outside the tube; and upflow of air approaching equilibrium with the sea at the reduced surface pressure inside the tube. The sensitivity of intensity to the type of upflow process and to the sea surface temperature is investigated. Intensities calculated with the TEE are shown to be consistent with observations and to be close to intensities calculated with more complex methods. The TEE method is simple and can help understand the basic mechanism responsible for surface pressure reduction and for energy production. The method is used to show that approximately 20% of the heat taken from the sea during a hurricane is converted to mechanical energy. Received December 4, 2000/Revised March 29, 2001     

DIURNAL VARIATION OF SST IN RELATION TO SEASON AND WEATHER PHENOMENA IN THE BOHAI REGION

This study investigated the relationships between sea surface temperature(SST) and weather phenomena in different seasons in the Bohai region(China). Five categories of weather phenomena were screened(i.e., fine, cloudy,foggy, rainy and windy conditions) and their relationships with the difference between air temperature and SST observed at Oil Platform A during 2003-2010 were analyzed statistically. The effects of the difference between air temperature and SST in different weather phenomena were examined using the flux method of the atmospheric boundary layer and a formula for the difference between air temperature and SST. The results revealed diurnal variation of the difference between air temperature and SST of-1.0 to +1.0 ℃, i.e., air temperature above the sea surface is subtracted from the SST in corresponding weather phenomena in different seasons in the Bohai region. Moreover,according to the formula for the difference between air temperature and SST, wind and shortwave radiation are the most important factors in terms of the effects of SST on weather processes. In conclusion, the effects of SST on weather phenomena are manifest via the exchange of momentum and energy from sea to air. When the air temperature above the sea surface is lower than the SST, the SST helps develop mesoscale convection systems within the synoptic system through moisture and sensible heat fluxes. When the air temperature above the sea surface is greater than the SST,synoptic systems transfer energy into the sea through heat flux, which affects SST variation. Moreover, a mesoscale convection system will weaken if the synoptic system passes over a colder underlying surface.     

Available potential energy of the daily coastal circulation at Zadar (Croatia)

Summary The aim of this study is the evaluation of the sea breeze speed on the basis of its energy. Energetics of the sea breeze can be studied by means of the available potential energy (APE). Part of this energy is transformed into the kinetic energy of the sea breeze. Some similarity exists between the large scale processes of the circulation and the small coastal air circulation due to the fact that both circulations are triggered by the same physics, i.e., solenoidal activity of the baroclinic atmosphere. To evaluate the sea breeze speed, APE was calculated by use of the Lorenz’s equation (1955), and which is possible if the coastal circulation is considered to be a closed system in a hydrostatic equilibrium. For calculations and verifications hourly sea-surface temperatures, near-ground air temperatures and wind speed measurements, as well as the radio-sounding measurements at 12 UTC were used at the Zadar station (ϕ = 44° 08′ N, λ = 15° 13′ E), which is situated in the central part of the eastern Adriatic coast. Two days with an undisturbed sea breeze circulation were extracted using the methods for minimizing other atmospheric influences. Calculated hourly near ground sea breeze speeds obtained in this way were higher than the measured ones. With the assumption that some of the APE is transformed into the kinetic energy it is possible to obtain characteristic speed of the developed sea breeze with small discrepancies to the near-ground measurements. If 6.6% of the mean daily near ground APE was taken to be transformed to the mean daily kinetic sea breeze energy on the 29th and 4.2% on the 30th September 2002, the best agreement was obtained with the mean daily measured near ground sea breeze speed. This range of values can be attributed to inability to extract precise values for the lapse-rate needed in the APE sea breeze calculations. Results show similarities to the general circulation of the atmosphere, since about 10% of the APE is transformed to the kinetic energy of the sea breeze. On the other hand calculated wind speed at the lower branch of the borderline coastal circulation was not dependent on the integral value of the APE over the land, but on its value at the near-ground level.     

A numerical world ocean general circulation model

This paper describes a numerical model of the world ocean based on the fully primitive equations. A “Standard” ocean state is introduced into the equations of the model and the perturbed thermodynamic variables are used in the modle’s calculations. Both a free upper surface and a bottom topography are included in the model and a sigma coordinate is used to normalize the model’s vertical component. The model has four unevenly-spaced layers and 4 × 5 horizontal resolution based on C-grid system. The finite-difference scheme of the model is designed to conserve the gross available energy in order to avoid fictitious energy generation or decay.The model has been tested in response to the annual mean surface wind stress, sea level air pressure and sea level air temperature as a preliminary step to its further improvement and its coupling with a global atmospheric general circulation model. Some of results, including currents, temperature and sea surface elevation simulated by the model are presented.     

中-美联合海气考察期间热带西太平洋的海面热量平衡

根据1986年1—2月中美海气考察船所获得的气象资料和其它海洋气象报告,本文计算了热带西太平洋海面的热量平衡,指出该区域海面供给大气的热量大于它从大气接受到的能量。是一个重要的热源区。同时指出,海洋向大气输送热量最显著的地区是出现在西太平洋西部的热带地区,即在 10°N、130—150°E附近。此外,在该海域内,确定海面热量平衡特性的两个最重要的因素应属潜热通量和太阳辐射通量。      

Time-dependent response of a zonally averaged ocean–atmosphere–sea ice model to Milankovitch forcing

An ocean–atmosphere–sea ice model is developed to explore the time-dependent response of climate to Milankovitch forcing for the time interval 5–3 Myr BP. The ocean component is a zonally averaged model of the circulation in five basins (Arctic, Atlantic, Indian, Pacific, and Southern Oceans). The atmospheric component is a one-dimensional (latitudinal) energy balance model, and the sea-ice component is a thermodynamic model. Two numerical experiments are conducted. The first experiment does not include sea ice and the Arctic Ocean; the second experiment does. Results from the two experiments are used to investigate (1) the response of annual mean surface air and ocean temperatures to Milankovitch forcing, and (2) the role of sea ice in this response. In both experiments, the response of air temperature is dominated by obliquity cycles at most latitudes. On the other hand, the response of ocean temperature varies with latitude and depth. Deep water formed between 45°N and 65°N in the Atlantic Ocean mainly responds to precession. In contrast, deep water formed south of 60°S responds to obliquity when sea ice is not included. Sea ice acts as a time-integrator of summer insolation changes such that annual mean sea-ice conditions mainly respond to obliquity. Thus, in the presence of sea ice, air temperature changes over the sea ice are amplified, and temperature changes in deep water of southern origin are suppressed since water below sea ice is kept near the freezing point.     

A Note on Wind Speed and sea State Dependence of the Heat Exchange Coefficient

Both mean and wave-induced motions generate turbulence in the air flow above sea waves. Assuming a local balance between production of turbulent kinetic energy and its dissipation, an explicit relation for the heat exchange coefficient CH is obtained. It is shown that CH follows a square-root dependence on the drag coefficient CD. However, the proportionality coefficient appears to depend on the sea state, expressed in terms of the coupling parameter. Dependence on the sea state suppresses the CD1/2 wind-speed dependence, and results in a marginal increase of CH with increase in the wind speed.     

Air–sea interaction and formation of the Asian summer monsoon onset vortex over the Bay of Bengal

In spring over the southern Bay of Bengal (BOB), a vortex commonly develops, followed by the Asian summer monsoon onset. An analysis of relevant data and a case study reveals that the BOB monsoon onset vortex is formed as a consequence of air–sea interaction over BOB, which is modulated by Tibetan Plateau forcing and the land–sea thermal contrast over the South Asian area during the spring season. Tibetan Plateau forcing in spring generates a prevailing cold northwesterly over India in the lower troposphere. Strong surface sensible heating is then released, forming a prominent surface cyclone with a strong southwesterly along the coastal ocean in northwestern BOB. This southwesterly induces a local offshore current and upwelling, resulting in cold sea surface temperatures (SSTs). The southwesterly, together with the near-equatorial westerly, also results in a surface anticyclone with descending air over most of BOB and a cyclone with ascending air over the southern part of BOB. In the eastern part of central BOB, where sky is clear, surface wind is weak, and ocean mixed layer is shallow, intense solar radiation and low energy loss due to weak surface latent and sensible heat fluxes act onto a thin ocean layer, resulting in the development of a unique BOB warm pool in spring. Near the surface, water vapor is transferred from northern BOB and other regions to southeastern BOB, where surface sensible heating is relatively high. The atmospheric available potential energy is generated and converted to kinetic energy, thereby resulting in vortex formation. The vortex then intensifies and moves northward, where SST is higher and surface sensible heating is stronger. Meanwhile, the zonal-mean kinetic energy is converted to eddy kinetic energy in the area east of the vortex, and the vortex turns eastward. Eventually, southwesterly sweeps over eastern BOB and merges with the subtropical westerly, leading to the onset of the Asian summer monsoon.     

On hurricane energy

Warm seawater is the energy source for hurricanes. Interfacial sea-to-air heat transfer without spray ranges from 100?W?m^?2 in light wind to 1,000?W?m^?2 in hurricane force wind. Spray can increase sea-to-air heat transfer by two orders of magnitude and result in heat transfers of up to 100,000?W?m^?2. Drops of spray falling back in the sea can be 2–4?°C colder than the drops leaving the sea, thus transferring a large quantity of heat from sea to air. The heat of evaporation is taken from the sensible heat of the remainder of the drop; evaporating approximately 0.3?% of a drop is sufficient to reduce its temperature to the wet bulb temperature of the air. The heat required to evaporate hurricane precipitation is roughly equal to the heat removed from the sea indicating that sea cooling is due to heat removal from above and not to the mixing of cold water from below. The paper shows how case studies of ideal thermodynamic processes can help explain hurricane intensity.     

山东半岛一次冷流暴雪过程的中尺度模拟与云微物理特征分析

本文以NCEP-FNL资料作为初始场和边界场,采用WRF中尺度模式对2010年12月29-30日发生在山东半岛的一次冷流暴雪过程进行数值模拟,并利用高时空分辨率模拟结果分析此次过程的中尺度特征和云微物理特征.模拟与分析结果表明,此次暴雪过程发生在较强的海气温差背景下,渤海海表对冷空气的增温增湿作用显著,通过湍流交换等作用向低层大气输送大量感热、潜热和水汽;水汽由渤海中部海域输送到山东半岛东北部地区,其上空水汽辐合层比较浅薄,集中在800 hPa以下,相对湿度饱和层和比湿高值维持的时间与强降雪时段一致;中尺度海岸锋的生消过程对冷流暴雪过程形成有着重要作用,水平方向上呈现为偏北风和偏西风的强辐合带,局地环流中的上升运动触发不稳定能量释放,直接决定暴雪的落区和强度,这是产生浅对流降雪的主要物理机制;云中水凝物粒子的高度在600 hPa以下,最大值出现在850～900 hPa之间与浅对流结构相对应;各水凝物粒子含量相差较大,以雪和霰最多.     

Climatic teleconnections with the equatorial pacific and the role of ocean/atmosphere coupling

Starting from the occurrence of a zonal Walker circulation supplementing the meridional Hadley cell, the concept of ultralong waves with diagonal upper troughs extending far into the Tropics is stressed. The model of equatorial upwelling with air‐sea coupling is critically discussed and a modification proposed. An intensification of the subtropical jet at the peak of the 1972 El Niño (as suggested by Rowntree's model calculations) has been verified.

Empirical studies deal with the large interannual and interdecadal variations of the energy fluxes at the air‐sea interface; time variations of the oceanic evaporation and sensible heat flux are greater than expected. Using spectrum analysis, the occurrence of a 5‐year periodicity in equatorial rainfall of the Pacific and Indonesia is demonstrated, together with a marked phase shift along the NE coast of New Guinea.     

Modeling of urban heat island and its impacts on thermal circulations in the Beijing–Tianjin–Hebei region,China

Through regulating the land–atmosphere energy balance, urbanization plays an important role in modifying local circulations and cross-border transport of air pollutants. The Beijing–Tianjin–Hebei (BTH) metropolitan area in northern China is frequently influenced by complex atmospheric thermal circulations due to its special topography and geographic position. In this study, the Weather Research and Forecasting (WRF) model combined with remote sensing is used to explore the urbanization impacts on local circulations in the BTH region. The urban heat island (UHI) effect generated around Beijing and Tianjin shows complex interactions with local thermal circulations. Due to the combined effects of UHI and topography, the UHI circulation around Beijing and valley breeze at the southern slopes of Yan Mountain are coupled together to reinforce each other. At the coastal cities, the increased land/sea temperature gradient considerably accelerates the sea breeze along Bohai Bay and moves the sea breeze front further inland to reach as far as Beijing. This study may lay a foundation for the better understanding of air pollutant dispersion on complex terrain.

     

On the contribution of spray droplets to evaporation

The effect of spray droplets in the marine surface layer on evaporation is considered. Independent evidence from energy constraints, from visibility and from sea salt content of air is used. The estimation shows that, except perhaps for hurricane wind strength, the increase of total evaporation from evaporating droplets is negligible. This is in agreement with recent experimental evidence.     

黄渤海一次持续性大雾过程特征和成因分析

利用日本MTSAT1R卫星数据、常规地面和高空观测数据、NCEP FNL客观再分析资料和NEARGOOS（NorthEast Asian Regional Global Ocean Observing System）的海表温度（SST）数据,分析了2010年5月31日至6月5日发生在黄渤海及周边地区的一次持续性海雾天气的形成、维持、消散特征及其物理机制。结果表明：大雾形成前低层水汽非常充沛,入海变性冷高压的稳定维持为这次持续性海雾过程提供了有利的背景条件,海雾在夜间辐射冷却作用下形成;大雾期间黄渤海     

The Impact of Sediment-Laden Snow and Sea Ice in the Arctic on Climate

Sea ice formed over shallow Arctic shelves often entrains sediments resuspended from the sea floor. Some of this sediment-laden ice advects offshore into the Transpolar Drift Stream and the Beaufort Gyre of the Arctic Basin. Through the processes of seasonal melting at the top surface, and the freezing of clean ice on the bottom surface, these sediments tend, over time, to concentrate at the top of the ice where they can affect the surface albedo, and thus the absorbed solar radiation, when the ice is snow free. Similarly, wind-blown dust can reduce the albedo of snow. The question that is posed by this study is what is the impact of these sediments on the seasonal variation of sea ice, and how does it then affect climate? Experiments were conducted with a coupled energy balance climate-thermodynamic sea ice model to examine the impact of including sediments in the sea ice alone and in the sea ice and overlying snow. The focus of these experiments was the impact of the radiative and not the thermal properties of the sediments. The results suggest that if sea ice contains a significant amount of sediments which are covered by clean snow, there is only a small impact on the climate system. However, if the snow also contains significant sediments the impact on sea ice thickness and surface air temperature is much more significant.     

Impacts of the Autumn Arctic Sea Ice on the Intraseasonal Reversal of the Winter Siberian High

During 1979–2015, the intensity of the Siberian high(SH) in November and December–January(DJ) is frequently shown to have an out-of-phase relationship, which is accompanied by opposite surface air temperature and circulation anomalies.Further analyses indicate that the autumn Arctic sea ice is important for the phase reversal of the SH. There is a significantly positive(negative) correlation between the November(DJ) SH and the September sea ice area(SIA) anomalies. It is suggested that the reduction of autumn SIA induces anomalous upward surface turbulent heat flux(SHF), which can persist into November, especially over the Barents Sea. Consequently, the enhanced eddy energy and wave activity flux are transported to mid and high latitudes. This will then benefit the development of the storm track in northeastern Europe. Conversely, when downward SHF anomalies prevail in DJ, the decreased heat flux and suppressed eddy energy hinder the growth of the storm track during DJ over the Barents Sea and Europe. Through the eddy–mean flow interaction, the strengthened(weakened)storm track activities induce decreased(increased) Ural blockings and accelerated(decelerated) westerlies, which makes the cold air from the Arctic inhibited(transported) over the Siberian area. Therefore, a weaker(stronger) SH in November(DJ) occurs downstream. Moreover, anomalously large snowfall may intensify the SH in DJ rather than in November. The ensemble-mean results from the CMIP5 historical simulations further confirm these connections. The different responses to Arctic sea ice anomalies in early and middle winter set this study apart from earlier ones.     

1990年初夏西太平洋暖水池区海面热量收支特征分析

根据TOGA计划,1990年初夏,中美两国科学工作者对18°N—10°S、120—165°E的热带西太平洋海区进行了科学考察,本文用这次考察的资料(包括总辐射、净辐射、海温、气温、气压、湿度、露点、风、云和海浪),计算了睛天和阴雨天、两个剖面(165°E经向剖面和赤道纬向剖面)以及整个考察区域的(昼夜)净辐射强度、感热和潜热通量、净热量通量和动量通量的日平均和日总量,并对热带西太平洋西部和东部进行了比较,发现西部比东部获得更多的太阳辐射能,这是热带西太平洋暖水池形成的直接原因之一。      

一个冰气相互作用数值模拟结果的可能统计解释

基于一个全球海-冰-气耦合模式的数值模拟结果,选取冬季格陵兰海海表面温度(SST)、海冰密集度、海表面感热通量等物理量以及3个相关区域海平面气压分别作经验正交函数展开,取第一模时间系数作相关分析。结果表明,上一年海冰密集度偏大(小)与来年的SST偏低(高)相联系,但二者同期相关性最大。当海气热通量交换变化超前一年时,其与SST相关性最大。模式最低层大气温度与海洋表面热通量之间的同时相关性最大,冬季模式最低层气温偏高(低)与海洋表面失去的感热、潜热通量偏少(多)相联系。气温、比湿都和冰岛低压区及格陵兰海的海平面气压相关性最强,冰岛低压气压偏低(高)与模式最低层气温和比湿偏高(低)相联系。所以,在海-冰-气年际尺度的相互作用中,主要关系是大气环流调整造成大气中云量和低层气温、湿度变化,进而影响海气界面上的通量交换,造成SST的变化。SST变化决定着海冰范围及海冰密集度的变化,但海冰变化时通过相变潜热的释放或吸收反过来对SST变化有较明显影响。     

Turbulence structure of sea breeze front and its implication in air pollution transport — Application of k-ɛ turbulence model —

A k- turbulence model was applied to a numerical simulation of sea breeze. The dynamical behaviors of eddy diffusivity, turbulent kinetic energy and its dissipation rate, associated with moving sea breeze front, were predicted and analyzed. Results demonstrated, for example, difference of the turbulence structure between thermal internal boundary layer and inland mixed layer, and the double maxima structures of turbulence-related quantities in their vertical profiles just behind sea breeze front. The properties of the computed sea breeze front agreed qualitatively with those of a gravity current in unstable environment, observed by Simpson et al. (1977). Furthermore, the possibility that air pollutants released in the sea breeze layer might be trapped within small circulating flow at the sea breeze front, and move with it was shown in an advection simulation of hypothetical fluid particles using flows obtained.     

冬春季格陵兰海冰变化与初夏中国气温/降水关系的初步分析

采用英国Hadley中心GISST海冰面积资料，NCEP／NCAR再分析资料以及中国地面降水和气温资料，运用EOF分解，小波分析和合成分析等方法，初步探讨了格陵兰岛两侧附近冬春季海冰面积变化特征及其与初夏6月中国气温和降水的关系，结果表明，格陵兰岛东西两侧海冰面积呈显著反相变化，并且具有明显的年际和年代际周期性振荡，冬春季格陵兰－寻威海海冰与初夏6月中国长江以北气温（降水）正相关（反相关），与长江以南气温（降水）反相关（正相关），而对于戴维斯海峡－拉布拉多海海冰则具有相反的相关型，大尺度500hPa环流合成分析初步表明，冬春季格陵兰附近海冰面积变化伴随着北极极涡环流和北半球阻塞高压的持续异常，海冰变化可能是影响初夏中国气温和降水的因子之一。