Variability of the water temperature in the western Wadden Sea on tidal to centennial time scales

Daily observations of the sea surface temperature in the Marsdiep tidal inlet, which connects the shallow Dutch western Wadden Sea with the deeper North Sea, already started in the summer of 1860, over 140 years ago. Since the year 2000 the sampling frequency has strongly increased because of the use of electronic sensors and data logging by computer. Analysis of these temperature data has revealed variations with time scales from tidal, daily, seasonal, inter-annual, to centennial. The tidal temperature variations are generated by advection of the seasonally varying temperature gradient between Wadden Sea and North Sea, while the daily variations are mainly caused by the daily variation of solar radiation. The seasonal variation in sea surface temperature only lags a few days behind the coastal surface air temperature, contrary to the sea surface temperature in the deeper nearby North Sea, which is delayed with about 1 month. The North Atlantic Oscillation index has been used as large-scale proxy for the atmospheric forcing of the Wadden Sea temperature. Only for the winter and spring a significant correlation is found between temperature and the winter index. However, this correlation is so strong that also the annual mean temperature is correlated significantly with the North Atlantic Oscillation. At longer time scales, from decadal to centennial, also large temperature variations are observed, of the order of 1.5 °C. However, these are not related to long-term changes of the North Atlantic oscillation. These long-term temperature changes involve a cooling of about 1.5 °C in the first 30 years of the record and a similar warming in the last 25 years. In between, these long-term changes were smaller and more irregular. Similar conclusions can also be applied to individual seasons as well as to the date of the onset of spring.     

Subsurface Water Masses in the Central North Pacific Transition Region: The Repeat Section along the 18° Meridian

A repeat hydrographic section has been maintained over two decades along the 180° meridian across the subarctic-subtropical transition region. The section is naturally divided into at least three distinct zones. In the Subarctic Zone north of 46°N, the permanent halocline dominates the density stratification, supporting a subsurface temperature minimum (STM). The Subarctic Frontal Zone (SFZ) between 42°–46°N is the region where the subarctic halocline outcrops. To the south is the Subtropical Zone, where the permanent thermocline dominates the density stratification, containing a pycnostad of North Pacific Central Mode Water (CMW). The STM water colder than 4°C in the Subarctic Zone is originated in the winter mixed layer of the Bering Sea. The temporal variation of its core temperature lags 12–16 months behind the variations of both the winter sea surface temperature (SST) and the summer STM temperature in the Bering Sea, suggesting that the thermal anomalies imposed on the STM water by wintertime air-sea interaction in the Bering Sea spread over the western subarctic gyre, reaching the 180° meridian within a year or so. The CMW in this section originates in the winter mixed layer near the northern edge of the Subtropical Zone between 160°E and 180°. The CMW properties changed abruptly from 1988 to 1989; its temperature and salinity increased and its potential density decreased. It is argued that these changes were caused by the climate regime shift in 1988/1989 characterized by weakening of the Aleutian Low and the westerlies and increase in the SST in the subarctic-subtropical transition region. This revised version was published online in August 2006 with corrections to the Cover Date.     

North Pacific Subtropical Mode Waters Observed in Long XBT Cross Sections along 32.5°N Line

The S/V Shoyo, of the Hydrographic Department, Japan Coast Guard, has conducted high-density expendable bathythermograph (XBT) measurements along the 32.5°N line in the North Pacific every year from 1990 to 1993 as a part of the Japanese-World Ocean Circulation Experiment (WOCE). These XBT data are analyzed here, focusing on year-to-year variations of the inventory and core layer temperature (CLT) of the North Pacific subtropical mode water (NPSTMW). Large year-to-year changes are found in the NPSTMW CLTs estimated in longitudes between 140°E and 160°E. CLT values were found of 17.4°C in 1990, 17.1°C in 1991, 17.3°C in 1992 and 17.6°C in 1993. Inspection of the wintertime westerlies over the formation area and sea surface temperature distribution revealed that this change in CLT can be qualitatively attributed to the strength of atmospheric cooling in the formation area in the previous winter. Although a large year-to-year variation of NPSTMW inventory was also found, it is hard to state any relationship between CLT and atmospheric forcing. There is a possibility that different observational seasons may affect the inventory. It has also been found that the thermocline depth in 1991 was shallower in the sea area east of 180° than in 1992 and 1993. Associated with this change, the North Pacific central mode water (NPCMW), characterized by thermostad with temperatures ranging from 14°C to 11°C, appears in the sea area east of 180° in the 1992 and 1993 cross sections. The 1993 cross section, which ranged from the Japanese coast to the west coast of North America, possessed another thermostad in the surface layer, with a temperature of about 17°C in the eastern part of the cross section, off California. This revised version was published online in August 2006 with corrections to the Cover Date.     

Variability of the Southern Hemisphere Subtropical Jet Stream in the Second Half of the 20th Century and Early 21st Century

Latitudinal position and wind speed of the Southern Hemisphere subtropical jet stream have been investigated on the basis of ERA-Interim, JRA-55, and NCEP–NCAR reanalysis data for 1948–2013. The analysis covers different time intervals in summer and winter seasons, as well as different spatial domains. It has been shown that the variability of the southern jet stream parameters in both winter and summer seasons is predominantly characterized by wind-speed weakening on the jet-stream axis and its poleward shift. The winter seasons of 2000–2013 identified a shift in the jet-stream axis toward the equator in the Atlantic (60°–0° W) and African (0°–60° E) sectors; the wind-speed increase in the Atlantic sector was statistically significant. The wind speed on the jet-stream axis in both winter and summer is closely related to the temperature difference in the upper tropospheric layer of 200–400 hPa between the latitudinal zones of 0°–30° S and 30°–60° S. A significant negative correlation (r = ?0.78) between wind speed and temperature difference has been revealed for the winter season in the upper tropospheric layer between the latitudinal zones of 30°–60° S and 60°–90° S, which can be explained by the Southern Annular Mode variability in this season. No such relationship has been found for the summer season.     

The vertical structure of the atmospheric boundary layer over the central Arctic Ocean

The tropopause height and the atmospheric boundarylayer （PBL） height as well as the variation of inversion layer above the floating ice surface are presented using GPS （global position system ） radiosonde sounding data and relevant data obtained by Chinas fourth arctic scientific expedition team over the central Arctic Ocean （86°-88°N, 144°-170°W） during the summer of 2010. The tropopause height is from 9.8 to 10.5 km, with a temperature range between -52.2 and -54.10C in the central Arctic Ocean. Two zones of maximum wind （over 12 m/s） are found in the wind profile, namely, low- and upper-level jets, located in the middle troposphere and the tropopause, respectively. The wind direction has a marked variation point in the two jets from the southeast to the southwest. The average PBL height determined by two methods is 341 and 453 m respectively. These two methods can both be used when the inversion layer is very low, but the results vary significantly when the inversion layer is very high. A significant logarithmic relationship exists between the PBL height and the inversion intensity, with a correlation coefficient of 0.66, indicating that the more intense the temperature inversion is, the lower the boundary layer will be. The observation results obviously differ from those of the third arctic expedition zone （800-85° N）. The PBL height and the inversion layer thickness are much lower than those at 870-88° N, but the inversion temperature is more intense, meaning a strong ice- atmosphere interaction in the sea near the North Pole. The PBL structure is related to the weather system and the sea ice concentration, which affects the observation station.     

Mixed layer variability in Northern Arabian Sea as detected by an Argo float

Seasonal evolution of surface mixed layer in the Northern Arabian Sea (NAS) between 17° N–20.5° N and 59° E-69° E was observed by using Argo float daily data for about 9 months, from April 2002 through December 2002. Results showed that during April - May mixed layer shoaled due to light winds, clear sky and intense solar insolation. Sea surface temperature (SST) rose by 2.3 °C and ocean gained an average of 99.8 Wm⁻². Mixed layer reached maximum depth of about 71 m during June - September owing to strong winds and cloudy skies. Ocean gained abnormally low ∼18 Wm⁻² and SST dropped by 3.4 °C. During the inter monsoon period, October, mixed layer shoaled and maintained a depth of 20 to 30 m. November - December was accompanied by moderate winds, dropping of SST by 1.5 °C and ocean lost an average of 52.5 Wm⁻². Mixed layer deepened gradually reaching a maximum of 62 m in December. Analysis of surface fluxes and winds suggested that winds and fluxes are the dominating factors causing deepening of mixed layer during summer and winter monsoon periods respectively. Relatively high correlation between MLD, net heat flux and wind speed revealed that short term variability of MLD coincided well with short term variability of surface forcing.     

华北地区夏季降雨量与南海海温长期变化的关系

比较了华北地区7个站与17个站1951-1997年夏季（6，7，8月）降雨量与气候随时间的变化特征，并对其成因作了探讨。结果表明，用北京、天津、邢台、烟台、郑州、太原和济南等7个站可代表该地区夏季降雨量与气候的多尺度变化特征，过去47a该地区依次经历了湿凉、湿热、湿凉、干热、湿热几个时期，降雨量的长期变化与南海前冬（1-2月）海温成负相关。前冬南海海温偏高，意味着初夏南海地区大气对流低频振动偏弱，南海夏季风爆发较晚，西南季风较弱，夏季西太平洋副高位置偏南，华北地区大气低层北风加强，华北地区夏季少雨，前冬南海海温偏低时情况则相反，考虑冬季（1-2月）南海南温和7-8月西太平洋副高脊线位置（纬度）的影响用均生函数建模，试验结果与用子波变换重构方法考虑华北地区夏季降雨量的变化趋势比较，二者相吻合，预测试验结果与过去3a的实况基本一致。     

New type of pycnostad in the western subtropical-subarctic transition region of the North Pacific: Transition Region Mode Water

A new type of pycnostad has been identified in the western subtropical-subarctic transition region of the North Pacific, based on the intensive hydrographic survey carried out in July, 2002. The potential density, temperature and salinity of the pycnostad were found to be 26.5–26.7 σ _θ , 5°–7°C and 33.5–33.9 psu respectively. The pycnostad is denser, colder and fresher than those of the North Pacific Central Mode Water and different from those of other known mode waters in the North Pacific. The thickness of the pycnostad is comparable to that of other mode waters, spreading over an area of at least 650 × 500 km around 43°N and 160°E in the western transition region. Hence, we refer to the pycnostad as Transition Region Mode Water (TRMW). Oxygen data, geostrophic current speed and climatology of mixed layer depth in the winter suggest that the TRMW is formed regularly in the deep winter mixed layer near the region where it was observed. Analysis of surface heat flux also supports the idea and suggests that there is significant interannual variability in the property of the TRMW. The TRMW is consistently distributed between the Subarctic Boundary and the Subarctic Front. It is also characterized by a wide T-S range with similar density, which is the characteristic of such a transition region between subtropical and subarctic water masses, which forms a density-compensating temperature and salinity front. The frontal nature also tends to cause isopycnal intrusions within the pycnostad of the TRMW.     

Property differences in the central northeastern Pacific between April 1976 and July 1977

Hydrographic data taken at 25 equally spaced stations along 35°N in April 1976 and again in July 1977 are compared for the longitude range 139–163° W and the depth range 0–1,000 m. A continuous subsurface layer is found, centered at 100 m and extending more than 2,000 km in the east-west direction, in which the temperature and salinity were significantly lower and the density and concentrations of oxygen and three nutrients were higher in the summer of 1977 than in the spring of 1976. In the upper 50 m the temperature and salinity were higher and the density and concentrations of oxygen and nutrients were lower in the summer of 1977 than in the spring of 1976. These relationships are concluded to be due to an annual variation by association with other existing data sets in the same region. The annual variation of hydrographic properties in the upper 200 m can be qualitatively explained by an annual variation in the north-south component of the permanent circulation, which is caused by an annual variation in the large-scale north-south pressure gradient (related to the northward temperature gradient). The observations are consistent with a northward current near the surface and a southward current near 100 m which are both faster in summer than in winter (and spring).     

Seasonal variability of the mixed layer in the central Bay of Bengal and associated changes in nutrients and chlorophyll

Hydrographic data from National Oceanographic Data Center (NODC) and Responsible National Oceanographic Data Centre (RNODC) were used to study the seasonal variability of the mixed layer in the central Bay of Bengal (8–20°N and 87–91°E), while meteorological data from Comprehensive Ocean Atmosphere Data Set (COADS) were used to explore atmospheric forcing responsible for the variability. The observed changes in the mixed-layer depth (MLD) clearly demarcated a distinct north–south regime with 15°N as the limiting latitude. North of this latitude MLD remained shallow (∼20 m) for most of the year without showing any appreciable seasonality. Lack of seasonality suggests that the low-salinity water, which is perennially present in the northern Bay, controls the stability and MLD. The observed winter freshening is driven by the winter rainfall and associated river discharge, which is advected offshore under the prevailing circulation. The resulting stratification was so strong that even a 4 °C cooling in sea-surface temperature (SST) during winter was unable to initiate convective mixing. In contrast, the southern region showed a strong semi-annual variability with deep MLD during summer and winter and a shallow MLD during spring and fall intermonsoons. The shallow MLD in spring and fall results from primary and secondary heating associated with increased incoming solar radiation and lighter winds during this period. The deep mixed layer during summer results from two processes: the increased wind forcing and the intrusion of high-salinity waters of Arabian Sea origin. The high winds associated with summer monsoon initiate greater wind-driven mixing, while the intrusion of high-salinity waters erodes the halocline and weakens the upper-layer stratification of the water column and aids in vertical mixing. The deep MLD in the south during winter was driven by wind-mixing, when the upper water column was comparatively less stable. The deep MLD between 15 and 17°N during March–May cannot be explained in the context of local atmospheric forcing. We show that this is associated with the propagation of Rossby waves from the eastern Bay. We also show that the nitrate and chlorophyll distribution in the upper ocean during spring intermonsoon is strongly coupled to the MLD, whereas during summer river runoff and cold-core eddies appear to play a major role in regulating the nutrients and chlorophyll.     

Hydrological conditions and circulation off the west coast of the North Island,New Zealand

Temperature and salinity surveys were carried out in the Tasman Sea in winter (August 1973) and summer (February‐March 1974). In both surveys the presence of the Westland Current was indicated by the distribution of surface water properties; in summer it was associated with a subsurface salinity maximum. The current extended further northwards in summer than in winter. In summer, an east‐going geostrophic flow at about latitude 35°S separated on approaching New Zealand; part of the flow passed north around the North Island and part moved slowly eastwards in the deeper off‐shore water to at least latitude 38°S. The West Auckland Current was apparent in the winter, but not in the summer. To the west of Cape Reinga, relatively low values of surface temperature and salinity are probably associated with upwelling between Cape Reinga and the Three Kings Islands. Upwelling was observed along the coast between Kaipara and Manukau Harbour.     

Current changes of the lower troposphere temperature in the Moscow region

Modern climatic changes for 1991–2013 in the lower 4-km layer of the atmosphere in the Moscow region are discussed based on long-term measurements using radiosondes in Dolgoprudny near Moscow and sensors installed on a high mast in Obninsk and on a television tower in Ostankino in Moscow. It is shown that at the end of the 20th century and the beginning of the 21st century the mean-annual air temperature at all heights from 2 to 4000 m increased by an average of 0.1°C per year. In recent years, the warming has slowed. Over the last two decades, long-term changes were multidirectional, depending on the season: warming in May–December, cooling in January–February, and no statistically significant changes in March and April. The probable reason for the temperature decrease in the middle of the cold period is changes in the large-scale atmospheric circulation during recent years (the negative phase of the North Atlantic Oscillation in early 2010s). In recent years, the Moscow region climate continentality has increased because of warming in summer and cooling in winter, despite the secular decreasing trend, which was noted before. Mean daily and annual warming rates in Dolgoprudny were higher than in Obninsk. The probable reason is the northward construction expansion and the strengthening of the Moscow heat island. The highest annual temperature amplitude is recorded at heights of 200–300 m.     

渤海中部海底恒温层温度及泥温相位随深度变化特征

利用渤海中部两点一年中４个季节泥温观测资料，近似确定两测点海底恒温层泥温分别为１１．０℃和１１．７℃。认国泥温随深度变化可视为一垂向波－泥温波，并利用这一概念分析了泥温相位随深度变化特征，８＾＃，Ａ（Ｂ）平台测点泥温波波长分别为ｌ８＝８ｍ和ｌＡ（Ｂ）＝１０ｍ。研究建议，以０．５ｍ处多年泥温平均值作为海底恒温层温度。     

Ocean temperature climate off North‐East New Zealand

The ocean temperature field off the north‐east coast of New Zealand is studied to quantify the annual cycle and reveal the intra‐ and inter‐annual variability. The data used are repeat expendable bathythermograph (XBT) sections between Auckland and either Suva or Honolulu which have been collected quarterly since 1986. These sections give temperature measurements between the surface and 800 m and Auckland and 30°S from 1986 to August 1999. The mean and annual cycle are compared with those from the NOAA World Ocean Atlas (WOA98). The results are similar; however WOA98 lacks the horizontal resolution to fully discern the East Auckland Current and North Cape Eddy, while the XBT analysis lacks the temporal resolution to discern higher frequency intra‐annual signals. The temperature variability in the mixed layer is dominated by the annual cycle, which accounts for 80–90% of the variance. The amplitude of the annual cycle diminishes rapidly with depth, from 2.8°C at the surface, to c. 0.1°C at 180 m. The phase of the annual cycle is retarded with depth, with peak temperatures occurring in February at the surface and in June/July at 180 m. Removing the annual cycle from the time series reveals the more subtle inter‐ and intra‐annual variability. This variability is of the order of 1°C in the upper 50 m, decreasing to 0.3°C at 400–500 m. The surface layer was cold between 1991 and 1994 (c. 0.7°C cooler than average), and 0.7°C warmer than average in 1999. The deeper ocean shows a different signal, being up to 0.3°C cooler in 1990–92, 0.3°C warmer in 1998, and c. 0.2°C warmer than average in 1999. The inter‐annual mixed layer variability is highly correlated with the Southern Oscillation Index and also with inter‐annual terrestrial air temperature and wind measurements from northern New Zealand. In contrast, at higher intra‐annual frequencies, the mixed layer variability is not correlated with air and wind measurements. At these higher frequencies, the air temperature is better correlated with the sea surface temperature (SST) than with the bulk mixed layer temperature.     

基于SODA资料的太平洋及我国周边海域温差能资源时空特征分析

基于简单海洋数据同化数据集的逐月再分析海温资料,对1971年1月至2010年12月共40年的太平洋及我国周边海域温差能资源的时空特征进行统计分析,得到以下主要结论:（1）温差季节变化特征明显,北半球的20℃等温差线从冬季到夏季可由20°N扩展到40°N,而南半球的温差受季节变化相对较小;温差能有效开采区域集中在30°S~40°N范围内,但纬向分布不均;可近似将气候态平均的20℃等温差线作为全年可开采区域的边界;（2）太平洋绝大部分海域的温差能等价深度呈逐年上升趋势,最大可达近2 m/a;温差能的变异系数具有明显季节变化特征但总体维持在较低水平,有效开采区域之内的变异系数在各季节均低于0.1;（3）我国温差能资源在南海及台湾以东海域最为丰富,其温差维持较高水平,能量密度总体呈逐年上升趋势,能量的稳定性较好且可实现全年有效开采,其最佳利用时间为5-7月,最差利用时间为2-3月;（4）太平洋温差能储量在TW量级,且以2.83 GW/a的趋势递增。     

Structure of temperature variability in the high latitudes of the Northern Hemisphere

The spatial structure of surface air temperature (SAT) anomalies in the extratropical latitudes of the Northern Hemisphere (NH) during the 20th century is studied from the data obtained over the period 1892–1999. The expansion of the mean (over the winter and summer periods) SAT anomalies into empirical orthogonal functions (EOFs) is used for analysis. It is shown that variations in the mean air temperature in the Arctic region (within the latitudes 60°–90°N) during both the winter and summer periods can be described with a high accuracy by two spatial orthogonal modes of variability. For the winter period, these are the EOF related to the leading mode of variability of large-scale atmospheric circulation in the NH, the North Atlantic Oscillation, and the spatially localized (in the Arctic) EOF, which describes the Arctic warming of the mid-20th century. The expansion coefficient of this EOF does not correlate with the indices of atmospheric circulation and is hypothetically related to variations in the area of the Arctic ice cover that are due to long-period variations in the influx of oceanic heat from the Atlantic. On the whole, a significantly weaker relation to the atmospheric circulation is characteristic of the summer period. The first leading variability mode describes a positive temperature trend of the past decades, which is hypothetically related to global warming, while the second leading EOF describes a long-period oscillation. On the whole, the results of analysis suggest a significant effect of natural climatic variability on air-temperature anomalies in the NH high latitudes and possible difficulties in isolating an anthropogenic component of climate changes.     

Seasonal and inter-annual variability in properties of surface water off Santander,Bay of Biscay, 1991–1995

The annual cycle of temperature, salinity and nutrients of surface waters (up to 100 m depth) was studied from June 1991 to December 1995 in a cross-shelf section over the continental shelf waters off Santander (southern Bay of Biscay). The time series showed that the temperature followed the expected seasonal warming and cooling pattern, which determines a seasonal process of stratification and mixing of the water column. The stratification period occurs annually between May and October in a layer of about 50 m depth from the neritic station beyond to the shelf-break. In the period between November and April the water column remained mixed. During spring and summer low salinity values were found in the surface due to continental runoff and advection from oceanic waters. In late autumn and winter, the salinity pattern was governed by an influx of salty water associated with the poleward current. As in other temperate latitudes, nitrates showed the highest values in winter throughout the water column and the lowest values at the surface during the stratified period. Wind-induced upwelling events were observed mainly in summer, which are characterised by low temperatures (< 12°C), high salinity and nutrient concentrations. The inter-annual variability of temperature showed a warming trend in the upper layers but this sign was not found at 100 m depth. In salinity a decreasing trend was observed throughout the water column, and this feature corresponds to the relaxing of the high salinity anomaly detected in the North Atlantic at the beginning of the 1990s. Both trends were coherent in the cross-shelf section from the coast to the slope.     

Seasonal variations of the upper ocean in the western north pacific observed by an argo float

A seasonal evolution of surface mixed layer in the western North Pacific around 24°N between 143°E and 150°E was observed by using an Argo float for more than 9 months, from December 2001 through August 2002. The result showed that the mixed layer deepened gradually in the first two months. It reached its maximum depth of about 130 m at the end of January, after which the mixed layer varied largely and sometimes the pycnocline below the mixed layer was much weakened until the summer mixed layer formed in late April. The thin surface mixed layer was maintained during the rest of the observation period. Heat budget analysis suggests that the vertical and horizontal temperature advections are the two most dominant terms in the heat balance in the upper layer on time scales from a few days to a month. The vertical motions that are possibly responsible for the vertical temperature advection are discussed.     

东亚夏季气候主要模态的年际变化及其机理

主要研究了东亚(中国和日本)夏季气候(降水和气温)主要模态的年际变化及其机理。研究发现,中国区域夏季降水和气温的大尺度年际变化间有很强的耦合:大范围多(少)雨对应大范围低(高)温。奇异值分解的第一个模态的长期变化主要反映了长江中下游地区降水逐年增加(变湿)的趋势而气温逐年降低(变冷)的趋势。在70年代中期以后,长江中下游地区降水和气温耦合变化的准两年分量明显增强。研究表明,影响长江中下游地区夏季降水和气温年际变化的大尺度环流背景异常十分相似,即主要是两个遥相关型:太平洋-日本(PJ)型和欧亚型遥相关型。与夏季东亚梅雨异常相联系的长江中下游地区降水和气温异常是中高纬度干冷空气和低纬度暖湿空气相互作用的结果。热带西太平洋海表温度异常和相关的对流活动的年际变化通过PJ型对东亚地区夏季降水和气温的年际变化产生十分显着的影响。西太平洋对流活动与北半球大气环流遥相关的相互作用有明显的季节性。PJ型不仅是夏季西太平洋对流活动与北半球夏季热带外地区500hPa高度场年际变化耦合相互作用的最重要模态,而且也是两者各自变化的一个十分重要的模态。1984年夏季北半球500hPa位势高度主振荡型分析表明存在着能量从热带西太平洋向东亚北部的PJ型的振荡传播。低纬度的影响可传播到70°N,同时也存在能量从高纬度向低纬度的传播.即从极地传播到70°N。高纬度和低纬度的影响在70°N附近汇合。     

Sea water temperature variation east of Taiwan

Temperature, wave and wind data over two years off Ho Peng, Shi Ti and Jang Yuan of east Taiwan are analyzed to study their seasonal variations. A model for predicting the mixed layer thickness is developed by use of wave data. The vertical profile of temperature indicates that there are basically three layers; mixed layer, thermocline layer and deep cold layer. The surface mixed layer appears in winter and disappears in summer. While surface water is warmer in summer than in winter, water at a depth of 50 m is warmer in winter than in summer. The seasonal variation in the deep cold layer is weak. The sea surface temperature is generally higher offshore than nearshore. The surface temperature off east Taiwan is almost equal to that in Taiwan Strait in summer, but in winter it is about 4°C warmer off northeast Taiwan than in the northeast of the Taiwan Strait, if compared at the same latitude. This is an effect of the seasonal variation of the Kuroshio. A model is developed for predicting the mixed layer thickness in terms of the input wave energy. The model successfully accounts for the observed features.