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Atmospheric cloud radiative effect (ACRE) is a critical heat source in the atmosphere, with pronounced regional distributions. Here, we investigate seasonal and interannual characteristics of ACRE over South China (SC) and neighbouring ocean regions using 2001–2020 satellite and reanalysis data. Annual mean net ACRE shows a warming role over most of SC, its eastern ocean (ESCO), and the South China Sea and western North Pacific (SWNP), with domain‐mean values of 6.0, 14.9, and 32.8 W m−2, respectively. Over SC, the shortwave ACRE warming dominates annual mean net ACRE, and considerable low‐middle clouds with small particle size and large water content reflect shortwave radiation and enhance shortwave absorption, especially in spring. Notably, winter longwave ACRE over SC, with a cooling role, strongly offsets its summer counterpart's warming role. In contrast, longwave ACRE mainly accounts for net ACRE over ESCO and SWNP, especially the latter where high clouds prevail. The Asian summer monsoon enhances summer high clouds and longwave (net) ACRE. Cloud types and complex vertical distribution associated with continental environments and the Tibetan Plateau's topography forcing enable seasonal behaviours of ACRE over SC to be different from the other two regions. Longwave ACRE dominates the interannual variation of net ACRE, with a larger interannual variability over SWNP, while a larger annual variability of shortwave ACRE occurs over SC. There are no significant interannual trends of ACRE except for annual and spring mean longwave (net) ACRE over SC. Moreover, the interannual variation of longwave (net) ACRE relates well to 500‐hPa vertical velocity, indicating the strong influence of large‐scale circulation on regional ACRE. [ABSTRACT FROM AUTHOR]

This study monitored spatiotemporal variation in aboveground biomass of a paddock (1.1 ha) in a sown tropical grass pasture under cattle grazing over a 22‐year period (1995–2016) by nondestructively estimating biomasses of 182 fixed locations (0.5 × 0.5 m each) in the paddock at about monthly intervals during the annual stocking season (May to October or November). The mean aboveground biomass of the paddock varied seasonally and interannually between 33 and 605 g DM/m2 and was explained by a regression model including positive effects of mean air temperature, N fertilizer rate and total precipitation during the preceding 60 days (R2 = 0.311, P < 0.001). The coefficient of variation of aboveground biomass, as an indicator of spatial (within‐paddock) variability, varied seasonally and interannually between 0.16 and 0.94, and was described by a model incorporating a positive effect of cumulative stocking density during the preceding 40 days and negative effects of mean air temperature, total precipitation during the preceding 20 days and N fertilizer rate during the preceding 60 days (R2 = 0.277, P < 0.001). The spatial distribution pattern of aboveground biomass in the paddock was persistent (P < 0.05) or not persistent over the study period, almost without being reversed. In detail, patterns in the mid stocking season tended to maintain mutual similarity in the entire range of the intervals between the measurements (364–7,694 days), whereas those at the beginning and near end of the stocking season lost mutual similarity as the interval increased. There was no indubitable evidence that the changes in botanical composition destabilized the spatial distribution pattern of aboveground biomass. The results indicate the need for assessing how the long‐term stability of the within‐paddock distribution pattern of aboveground biomass affects agronomic and ecological performance of the grazing system. [ABSTRACT FROM AUTHOR]

In the mesosphere and lower thermosphere (MLT) region, residual circulations driven by gravity wave breaking and dissipation significantly impact constituent distribution and the height and temperature of the mesopause. The distribution of CO2 can be used as a proxy for the residual circulations. Sounding of the Atmosphere using Broadband Emission Radiometry (SABER) CO2 volume mixing ratio (VMR) and temperature measurements from 2003 to 2020 are used to study the monthly climatology of MLT residual circulations and the mesopause height. Our analyses show that (a) mesopause height strongly correlates with the CO2 VMR vertical gradient during solstices; (b) mesopause height has a discontinuity at midlatitude in the summer hemisphere, with a lower mesopause height at mid‐to‐high latitudes as a result of adiabatic cooling driven by strong adiabatic upwelling; (c) the residual circulations have strong seasonal variations at mid‐to‐high latitudes, but they are more uniform at low latitudes; and (d) the interannual variability of the residual circulations and mesopause height is larger in the Southern Hemisphere (SH; 4–5 km) than in the Northern Hemisphere (NH; 0.5–1 km). Key Points: Monthly climatology of the mesopause height, and MLT CO2 gradients as signatures of the residual circulations are derived from SABER dataBoth the regions of maximum vertical CO2 gradients and mesopause height show strong seasonal variations at mid‐to‐high latitudesInterannual variations of the height of maximum vertical CO2 gradients and mesopause height are larger in the SH than in the NH [ABSTRACT FROM AUTHOR]

A more objective assessment of the freshwater scarcity risk at a watershed basis scale contributes to the achievement of the Sustainable Development Goals (SDGs), in which water plays a key role in issues like safe and affordable drinking water, water-related disasters, forest management, biodiversity and ecosystems. Within the SDGs, water scarcity is assessed primarily by using the ratio of withdrawal to availability (WTA). This index has been developed to evaluate the average annual conditions on a broad scale, such as country or large basin. However, there are insufficient cases for assessing specific and detailed risk conditions by using this original WTA concept, due to seasonal and interannual variations of the river discharge and withdrawal volumes. For example, infrastructure (e.g. large dams) and its operation, can drastically change the available water and demand volumes at temporal scales finer than annual. Because recently many daily and monthly records of river discharge and water use have become publicly available, it is possible to conduct water scarcity risk assessments on a monthly basis. By employing these datasets, in this study, we propose to compare volumes of available water and demand by using a Sectoral and Statistical Demand to Availability (SS-DTA) index. The novelty of this index is marked not only by the use of monthly volumes of available and required water but also by how environmental water requirements are included and the statistical relevance of the evaluation. Usually, to determine the available water resources, existing methods deduct from the river discharge the volumes that are required to preserve the surrounding ecosystems. Our proposed method considers the environmental flow requirements as one of the water-demand sectors allowing a simultaneous evaluation of water use that is not possible with existing methods. We applied this method to three representative river basins, two located in Japan (the Tone and the Arakawa River basins) and the Brantas River basin in Indonesia. The results showed the variations of water scarcity risk level through the river operation in each river basin. In the Tone River basin, it was succeeded in a drought year to decrease its risk level from 1 to 0, and to transport sufficient volume of water to the Arakawa River basin through an artificial channel to meet the demands at the same time. In the Brantas River basin, the river operation changed the SS-DTA score from 3 to 2, which means the water scarcity risk level was alleviated, while the main impact of the operation was found in high-water season to decrease the flood risk. Because the number, type, and priority of water demands can be adjusted based on the local situation and all the timeseries data of each demand sector are visualized in parallel, the result includes not only the whole risk level of the river basin but also the practical and specific degree of the risk with demand sector information.

In this study, we use the long-term satellite data to investigate seasonal and interannual variation of low-cloud fraction (LCF) and the associated controlling factors over the eastern and western North Pacific. On the seasonal time scale, the enhanced LCF over the eastern North Pacific in summer is actively coupled with strong estimated inversion strength (EIS) and 700-hPa relative humidity, and the LCF over the western North Pacific in winter is large and mainly caused by increased sensible heat flux and tropospheric low-level cold advection. On the interannual time scale, the increased LCF over the eastern North Pacific in summer is associated with increased EIS and decreased sea surface temperatures, in which the El Niño plays an important role; the enhanced LCF over the western North Pacific in spring and winter has a positive correlation with enhanced sensible heat flux (SHF) and tropospheric low-level cold advection, which can be partly explained by the subpolar frontal zone (SPFZ) intensity.

Tropical vegetation has been suggested to be vulnerable to future climate change. At the regional scale, few studies have focused on the fluctuations of vegetation activity of tropical forests in Southeast Asia, which is an important area of tropical vegetation. Here, we investigated the spatio-temporal variability of vegetation photosynthetic activity in Southeast Asia using three independent satellite-derived Normalized Difference Vegetation Index (NDVI) products (Global Inventory Modeling and Mapping Studies group using data from Advanced Very High Resolution Radiometer (GIMMS AVHRR) NDVI3 g, Système Pour l’Observation de la Terre VEGETATION (SPOT-VGT), and MODerate resolution Imaging Spectroradiometer (MODIS)). We also used the recently developed Sun-Induced chlorophyll Fluorescence (SIF) from the Greenhouse gases Observing SATellite (GOSAT), a proxy of actual photosynthesis, as a complement to NDVI. In forests with pronounced wet-dry seasonal cycle (the north and south regions of Southeast Asia), we found consistent relationships between NDVI and climate factors (precipitation, temperature and solar radiation). At the seasonal scale, all of the datasets showed that the NDVI continuously decreased during the dry season, particularly in deciduous forests (DF). Similarly, SIF in the north region also displayed a decreasing trend during the dry season, although the magnitude of the decrease was relatively small compared to that of the NDVI. This result is in contrast to that reported for the Amazon forest where a significant increase in vegetation greenness during the dry season has been observed. During the wet season, different seasonal variations were observed between SIF and the NDVI in the north region. For both evergreen forests (EF) and DF, the maximum SIF was observed in the months with the maximum precipitation, while the maximum NDVI value was observed at the end of the wet season. At the interannual scale, NDVI decrease nonlinearly along drought severity in dry seasons. During wet seasons, the greenness is insensitive to droughts but more related to radiation. Our results demonstrate that forests in Southeast Asia are water-limited during the dry season, indicating a vulnerability to future increase in the intensity of El Nino events and to temperature-driven increases in evapotranspiration. [ABSTRACT FROM AUTHOR]

Model output from a Pacific basin-wide three-dimensional physical-biogeochemical model during the period of 1991 to 2008 was used to investigate the impact of Kuroshio water on the source water of the southeastern Taiwan Strait. Based on the characteristic salinities of both Kuroshio water and the South China Sea water, a Kuroshio impact index (KII) was designed to measure the degree of impact. The KII correlates significantly with the northeast-southwest component of wind stress, but the former lags the latter by approximately two months. The correlation coefficient between them increases from 0.267 4 to 0.852 9, with a lag time increasing from 0 to 63 days. The impact of Kuroshio Water is greater in winter and spring than in summer and autumn. At the interannual time scale, El Niño and La Niña events play an important role in impacting the KII. During El Niño events, more Kuroshio water contributes to the source water of the southeastern Taiwan Strait. Conversely, during La Niña events, less Kuroshio water contributes to the source water. [ABSTRACT FROM AUTHOR]

Spatial and temporal (seasonal and interannual) variation in microphytoplankton was investigated at two tropical coral reef sites off Mauritius (Belle Mare [BM] and Flic-en-Flac [FEF]), from 2010 to 2012. Each site was divided into three zones: coast, lagoon and reef. Microphytoplankton, nutrient and chlorophyllasamples were collected, and physico-chemical parameters were measuredin situ. A total of 56 microphytoplankton genera were identified (43 diatoms, 8 dinoflagellates and 5 cyanobacteria). Total microphytoplankton density exhibited spatial and temporal variation, being higher at BM and near the coast, and mostly high in summer. Nutrient concentrations were highest near the coast as a result of run-off events and anthropogenic inputs, especially during heavy rainfall, and this resulted in elevated total microphytoplankton density. There were no clear diversity patterns at the two sites or within the different zones. At both sites,Navicula, CocconeisandFragilariawere the dominant diatoms, andGymnodinium, AlexandriumandProtoperidiniumwere the dominant dinoflagellates. There was a shift in dominance fromNaviculain summer toFragilariain winter. This seasonal shift may reflect how these species respond differently to environmental change, which could have implications for primary production at spatial and temporal scales. [ABSTRACT FROM AUTHOR]

Tropospheric ozone observations over China from 2005 to 2010 at three pressure levels (484, 681 and 825 hPa) from the Tropospheric Emission Spectrometer on board the NASA Aura satellite have been analyzed. Fourier Transform analysis revealed the trends and seasonality of regionally-averaged, monthly-mean ozone concentrations over western, northern and southern China. Significant increases in ozone levels are found over all three regions at 464 hPa and the rate of increase is fastest over northern China, reaching 0.89±0.059 nL/(L a). At 681 hPa, ozone shows increases over northern and western China, at a rate of 0.57± 0.065 nL/(L a) and 0.41±0.041 nL/(L a) respectively, but is constant over southern China. At 825 hPa, ozone increases at a rate of 0.36±0.074 nL/(L a) over northern China, while decreasing over southern China at a rate of −0.21±0.061 nL/(L a). Over the three regions, ozone levels are generally higher in summer and lower in winter. Over southern China at all three pressure levels and northern China at the 825 hPa level, ozone shows double peaks occurring in spring and autumn as a result of the combined effects of atmospheric chemistry and global transport. This work provides a useful observational dataset and tools for future analysis of changes in tropospheric ozone over China. [ABSTRACT FROM AUTHOR]

Spatiotemporal characteristics of interannual temperature variations in the Tsushima Strait are investigated on the basis of historical hydrographic data applying the same procedures as Senjyu et al. (2006). Empirical orthogonal function (EOF) analysis revealed that the most energetic mode of variation (the EOF first mode), which accounts for about 31.5% of the total variance, is the in-phase temperature change for the entire strait. The wintertime temperature variation described by the first mode is associated with the wintertime heat flux in the northern East China Sea, while they are poorly correlated in other seasons. The large standard deviation in the time coefficient of the first mode in August suggests a relationship with the horizontal heat advection in summer in the northern East China Sea. On the other hand, the EOF second mode, which explains about 12.6% of the total variance, is associated with the stratification and baroclinicity in the strait. The time coefficient of the EOF second mode negatively correlates with the baroclinic volume transport through the strait in summer. Comparison of temporal variations among the leading EOF modes for temperature and salinity shows no significant correlations. This indicates that the principal modes of variation in temperature and salinity vary independently within an interannual timescale. [ABSTRACT FROM AUTHOR]

Abstract: In extra-Andean Patagonia, wet meadows contrast with the prevailing arid steppes, and present a gradient of water availability from the periphery to the center. The objectives of this paper are to describe the spatial and temporal variation of aerial net primary production (ANPP) of Patagonian meadows, and to obtain a model for the relationship between the normalized difference vegetation index (NDVI) and ANPP. We determined ANPP in four regionally scattered meadows during 3–5 years and in three positions of the gradient of water availability. In one meadow, we correlated ANPP with NDVI during 2 years. Annual ANPP was 2–3 times larger in the center than in the periphery, and also varied 2–3 fold among the four meadows. The interannual variation of ANPP was high and similar across meadows and zones. ANPP was closely correlated with NDVI through a linear model. Within the growing season, the central zone had a more extended period of high NDVI into the summer than the peripheral and the intermediate zones. We conclude that (1) the local variation of ANPP across the gradient of water availability is strong and must be taken into account for management, and (2) the highly variable ANPP may be monitored by remote sensing. [Copyright &y& Elsevier]

Phytoplankton seasonal and interannual variability in the Guadiana upper estuary was analyzed during 1996-2005, a period that encompassed a climatic controlled reduction in river flow that was superimposed on the construction of a dam. Phytoplankton seasonal patterns revealed an alternation between a persistent light limitation and episodic nutrient limitation. Phytoplankton succession, with early spring diatom blooms and summer-early fall cyanobacterial blooms, was apparently driven by changes in nutrients, water temperature, and turbulence, clearly demonstrating the role of river flow and climate variability. Light intensity in the mixed layer was a prevalent driver of phytoplankton interannual variability, and the increased turbidity caused by the Alqueva dam construction was linked to pronounced decreases in chlorophyll a concentration, particularly at the start and end of the phytoplankton growing period. Decreases in annual maximum and average abundances of diatoms, green algae, and cyanobacteria were also detected. Furthermore, chlorophyll a decreases after dam filling and a decrease in turbidity may point to a shift from light limitation towards a more nutrient-limited mode in the near future. [ABSTRACT FROM AUTHOR]

Fifteen years of merged altimetric data were used to acquire the seasonal to interanual variations of eddy kinetic energy (EKE) in the South China Sea (SCS). The results show that climatological mean EKE in the SCS ranges from 50 cm2/s2 to 1,400 cm2/s2, with high values in the regions southeast of Vietnam and southwest of Taiwan Island. The amplitude of the annual harmonic of the EKE is characterized by high values to the southeast of Vietnam where the maximum exceeds 800 cm2/s2. The EKE in the northern SCS reaches its maximum in August-February, while it peaks in September–December in the southern SCS. Besides the seasonal variation, the EKE also shows strong interannual variation, which has a negative (positive) anomaly in boreal winter during El Niño (La Niña) events. The interannual variation of local wind stress curl associated with El Niño-Southern Oscillation events may be the cause of the interannual variation of the EKE in the SCS. [ABSTRACT FROM AUTHOR]

Abstract: Airglow intensities and rotational temperatures of the OH(6-2) and O2 b(0-1) bands acquired at El Leoncito (32°S, 69°W) provide good annual coverage in 1998–2002, 2006, and 2007, with between 192 and 311 nights of observation per year. These data can therefore be used to derive the seasonal variations during each of these seven years, in airglow brightness and temperatures at altitudes of 87 and 95km. From 1998 to 2001, seasonal variations are similar enough so that they can be well represented by a mean climatology, for each parameter. On the other hand, these climatologies do not agree with what is usually observed at other sites, maybe due to the particular orographic conditions at El Leoncito. With respect to the last three fully documented years (2002, 2006, and 2007), the similarity from year to year deteriorates, and there are greater differences in the seasonal behaviour, more or less in all the parameters. The differences include, e.g., maxima occurring earlier or later than “normal”, by one or two months. All this may suggest the build-up of a new regime of intraseasonal variability, with a possible relationship to corresponding changes in wave activity. [Copyright &y& Elsevier]

Temperature and salinity data from 2003 through 2006 from Argo profiling floats have been analyzed to examine the formation and circulation of the North Pacific Subtropical Mode Water (STMW) and the interannual variation of its properties over the entire distribution region. STMW is formed in late winter in the zonally-elongated recirculation gyre south of the Kuroshio and its extension, which extends north of ∼28°N, from 135°E to near the date line. The recirculation gyre consists of several anticyclonic circulations, in each of which thick STMW with a characteristic temperature is formed. After spring, the thick STMW tends to be continually trapped in the respective circulations, remaining in the formation region. From this stagnant pool of thick STMW, some portion seeps little by little into the southern region, where southwestward subsurface currents advect relatively thin STMW as far as 20°N to the south and just east of Taiwan to the west. The STMW formed in the recirculation gyre becomes colder, less saline, and denser to the east, with an abrupt change of properties across 140°E and a gradual change east of 140°E. The STMW formed east of 140°E exhibits coherent interannual variations, increasing its temperature by ∼1°C from 2003 through 2006 and also increasing its salinity by ∼0.05 from 2003 through 2005. These property changes are clearly detected in the southern region as far downstream as just east of Taiwan, with reasonable time lags. [ABSTRACT FROM AUTHOR]

Abstract: Biweekly composite averages of the standing stock of sea-surface chlorophyll (SSC) were derived from SeaWiFS satellite ocean-color data at 44 benthic sampling stations occupied along the continental slope and rise by the Deep Gulf of Mexico Benthos (DGoMB) program. At the 22 DGoMB sites north of 26°N and west of 91°W in the NW Gulf of Mexico, annual average SSC was 0.19mgm−3, ranging at most locations from annual highs of about 0.3mgm−3 in November–February to lows of about 0.1mgm−3 in May–August. Comparison of three years of SeaWiFS data (January 1998–December 2000) showed little inter-annual variation at these NW Gulf stations. In contrast, at the 22 NE Gulf sites north of 26°N and east of 91°W, SSC averaged 2.8 times higher than in the NW Gulf, showing also strong inter-annual variation. Maxima in the NE region occurred in November–February and also during summers. The summer maxima were associated with Mississippi River water transported offshore to the east and southward by anticyclonic eddies in the NE Gulf. The apparent increases in SSC in June–August at NE Gulf stations reached average monthly concentrations >50% greater than in November–February. Based on a primary productivity model and a vertical flux model, the calculated export of particulate organic carbon (POC flux reaching the seafloor) was estimated as ∼18mgCm−2 day−1 at the 22 NE Gulf stations, and ∼9mgCm−2 day−1 at the 22 NW Gulf stations. These estimates are comparable to fluxes measured by benthic lander by others in the DGoMB program, which may drive the differences in west versus east bathymetric zonation and community structure of macrobenthos that were sampled with large box corers by others in the DGoMB program. [Copyright &y& Elsevier]

Question: How do meteorological variations at seasonal, interannual scales differentially affect the canopy dynamics of four contrasting landscape units within a region? Location: Flooding Pampa, Buenos Aires, Argentina. 5000 km². Central point: 35°15' S, 57°45' W. Methods: We used a 19-year series of the normalized difference vegetation index (NDVI) derived from NOAA-AVHRR PAL (Pathfinder AVHRR Land) images and meteorological data provided by a nearby weather station. The NDVI was used as surrogate of canopy photosynthetic status. The relationship between annually integrated NDVI and meteorological conditions was explored by stepwise multiple regressions for each defined unit. PCA was performed to compare units and growing seasons on a multivariate basis. Results: Mean seasonal NDVI curve was similarly shaped among landscapes. However, the absolute values differed widely. There was high interannual variation so that the mean seasonal pattern was seldom observed in any particular year. Annually integrated NDVI of all landscapes was negatively associated with summer temperature and positively with previous year precipitation. It was also directly related with current year winter precipitation in two landscapes and with summer precipitation in the others. NDVI response to September and March precipitation accounted for some of the differences in interannual variation among landscapes. Conclusions: Our results revealed a strong intra-regional variation of canopy dynamics, closely linked to landscape (vegetation-soil) and water availability (mainly in summer and during the previous year). These links may be used to predict forage production rates for livestock. [ABSTRACT FROM AUTHOR]

During the 1990s many studies on zooplankton in the Japan Sea have been carried out. In this review, I have synthesized the study of horizontal distribution, seasonal and annual variations of zooplankton biomass, and ecological characteristics of major component species in the southern Japan Sea, which area is influenced by the warm Tsushima Current. The zooplankton biomass (annual mean) in the southern Japan Sea was lower than in the subarctic Pacific, including the northern Japan Sea, and similar to biomass levels in Kuroshio waters. Temporal variations in zooplankton biomass showed both seasonal and year-to-year components. Seasonal biomass increases to a maximum in spring with a weak secondary peak in autumn. As for long-term changes, 3–6 year cycles were identified, with the dynamics of the surface warm Tsushima Current and the subsurface cold water playing important roles in determining the yearly zooplankton community structure and biomass. Cold water species in the southern Japan Sea had extensive diel vertical migrations whose range is restricted in summer by the development of a thermocline. Among these species, the herbivores Euphausia pacifica and Metridia pacifica encounter a lower food supply, resulting in lower growth rates. The vertical dispersal of epipelagic carnivorous zooplankton such as Sagitta elegans and Themisto japonica to the deep-sea is probably facilitated by reduced interspecific competition. Their interaction with Japan Sea Proper Water, characterized by near-zero temperatures in the meso- and bathypelagic zones suppresses growth rates of the mesopelagic zooplankton. The lack of micronektonic predators in the mesopelagic zone may allow the persistence of slow growing populations. [Copyright &y& Elsevier]

Fish assemblages on two inshore rocky subtidal sites on the west coast of Scotland, were studied using diver visual surveys on a monthly basis between September 1995 and December 1999. A total of 17 689 fishes and 26 species were recorded from the two sites, Saulmore Point (056°27′ N; 005°24′ W) near Oban and Davy''s Rock (055°46′ N; 004°53′ W) on the Isle of Great Cumbrae. The gobiidThorogobius eppiphiatus , dominated the Saulmore Point site; six fish species accounted for >93% of total abundance at that site. At Davy''s Rock four species contributed at least 93% of total fish abundance, and the dominant species was the labrid Ctenolabrus rupestris. Total abundance of the dominant species displayed a clear seasonal trend, and this was significantly related to recorded daily average seawater temperature. A maximum abundance of 4·9 fishes m−2 was recorded in November 1998 at Davy''s Rock and 2·5 fishes m−2 at Saulmore Point in October 1998. Multivariate analysis indicated a degree of variation in assemblage structure between winter and summer at both sites. A number of species showed some degree of interannual variation, in particular the gobiidGobiusculus flavescens whose abundance increased by over 300 times over a 5 month period in 1998. Correlation analysis showed that variation in annual winter seawater temperature could act as an indicator of interannual variation in abundance of some of the dominant species utilizing rocky subtidal habitats. Copyright 2002 The Fisheries Society of the British Isles. Published by Elsevier Science Ltd. All rights reserved. [Copyright &y& Elsevier]

In this paper, the authors define the spring monsoon in South China, and study the climatology and the interannual variation through analysis of the precipitation and the related atmospheric circulation, as revealed by the NCEP/ NCAR reanalysis data. The results indicate that the spring monsoon season in South China occurs climatologically in April and May, which is supported by both seasonal and interannual variation of the atmospheric circulation and precipitation. The related atmospheric circulation is different from that during the East Asian summer or winter monsoon season. The interannual variation of the spring monsoon rainfall in South China relates primarily to the anomalous circulation over the North Pacific, which is linked with the westerly jet over North Asia and with the polar vortex. It is also connected with sea surface temperature anomalies in the Pacific. Changes in the Asian tropical atmospheric circulation has little influence on the spring monsoon in South China according to this research. [ABSTRACT FROM AUTHOR]

Quarterly data of CTD at the PN line in the East China Sea during 1988–94 were analyzed to examine the variations of water properties and density structure in relation to the Kuroshio. The Kuroshio flows over the continental slope at the PN line. Water properties in the surface layer less than 100 db change greatly and show a clear seasonal cycle, while those in the subsurface layer are much less variable. The small isobaric variations in the subsurface layer are almost due to the vertical movement of isopycnals, on which the water properties vary little. The subsurface variations of salinity, temperature and isopycnal depth are classified into four groups occurring in the four regions, divided vertically by the middle of the main pycnocline and horizontally by the offshore edge of the Kuroshio, named Groups 1 (upper Kuroshio), 2 (upper offshore region), 3 (lower Kuroshio), and 4 (lower offshore region). The difference in averaged isopycnal depth between Groups 1 and 2 (3 and 4) is highly correlated with the vertical shear of the Kuroshio velocity in the upper (lower) pycnocline. The isopycnal depth of Groups 1 and 3 has little annual cycle (with large intraseasonal variations in Group 3), while that of Groups 2 and 4 shows a clear seasonal variation with the minimum in fall. As a result, the Kuroshio velocity is smallest in fall almost every year, although the amplitude of seasonal variation and the season of maximum velocity are different from year to year. Interannual variations of isopycnal depth are characterized by a large amplitude of Group 2 and an opposite phase between Groups 3 and 4, so that the variations of difference in isopycnal depth between Groups 1 and 2 and Groups 3 and 4, i.e., the upper and lower shear of the Kuroshio velocity, are comparably significant. [ABSTRACT FROM AUTHOR]

A three-dimensional numerical model is used to simulate sea level and velocity variations in the South China Sea for 1992–1995. The model is driven by daily wind and daily sea surface temperature fields derived from the NCEP/NCAR 40-year reanalysis project. The four-year model outputs are analyzed using time-domain Empirical Orthogonal Functions (EOF). Spatial and temporal variations of the first two modes from the simulation compare favorably with those derived from satellite altimetry. Mode 1, which is associated with a southern gyre, shows symmetric seasonal reversal. Mode 2, which contributes to a northern gyre, is responsible for the asymmetric seasonal and interannual variations. In winter, the southern and northern cyclonic gyres combine into a strong basin-wide cyclonic gyre. In summer, a cyclonic northern gyre and an anticyclonic southern gyre form a dipole with a jet leaving the coast of Vietnam. Interannual variations are particularly noticeable during El Niño. The winter gyre is generally weakened and confined to the southern basin, and the summer dipole structure does not form. Vertical motions weaken accordingly with the basin-wide circulation. Variations of the wind stress curl in the first two EOF modes coincide with those of the model-derived sea level and horizontal velocities. The mode 1 wind stress curl, significant in the southern basin, coincides with the reversal of the southern gyre. The mode 2 curl, large in the central basin, is responsible for the asymmetry in the winter and summer gyres. Lack of the mode 2 contribution during El Niño events weakens the circulation. The agreement indicates that changes in the wind stress curl contribute to the seasonal and interannual variations in the South China Sea. [ABSTRACT FROM AUTHOR]

Chemical oxygen demand (COD) at the sea surface in Tokyo Bay was examined using monthly data during 1980–89. The long-term mean and the annual-cycle amplitude of COD are largest in the northwestern region, decrease southward, and are smallest near the entrance of the bay. Based on their spatial properties, Tokyo Bay was divided into northwest, northeast, southwest, and southeast regions, named Regions 1, 2, 3, and 4, respectively. The time mean and the annual-cycle amplitude are large in Regions 1 and 2 but much less in Region 4, and are highly correlated in Region 1 + 2 + 4. The annual-cycle amplitude in Region 3 is larger than that in Region 4, although the time mean is similar. The monthly long-term averages show a clear seasonal change of COD, with a large increase from April to June, the maximum in June, and the minimum in December. After the maximum, COD in Regions 1 and 3 (western side of the bay) decreases monotonically, while that in Regions 2 and 4 (eastern side) has a secondary maximum in August. The phase of annual cycle lags southward from the head to the mouth of the bay with a maximum lag of about one month. Anomalously large COD was observed in the western region of Tokyo Bay mostly in June, but never in the east and from July to April. This is related to a high concentration of chlorophyll a plus phaeo pigment and is likely caused by blooming of phytoplankton. Yearly mean COD was at a maximum in 1984 or 1985 and decreased greatly after that. The annual frequency of the observed anomalous COD was large in 1981, 1983, and 1985, then decreased abruptly, remaining small after 1985, possibly associated with low COD. [ABSTRACT FROM AUTHOR]

In this study, we use the long-term satellite data to investigate seasonal and interannual variation of low-cloud fraction (LCF) and the associated controlling factors over the eastern and western North Pacific. On the seasonal time scale, the enhanced LCF over the eastern North Pacific in summer is actively coupled with strong estimated inversion strength (EIS) and 700-hPa relative humidity, and the LCF over the western North Pacific in winter is large and mainly caused by increased sensible heat flux and tropospheric low-level cold advection. On the interannual time scale, the increased LCF over the eastern North Pacific in summer is associated with increased EIS and decreased sea surface temperatures, in which the El Niño plays an important role; the enhanced LCF over the western North Pacific in spring and winter has a positive correlation with enhanced sensible heat flux (SHF) and tropospheric low-level cold advection, which can be partly explained by the subpolar frontal zone (SPFZ) intensity. [ABSTRACT FROM AUTHOR]