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In this paper, temporal variability and trends of sea ice in the Kara Sea and their correlations with local atmospheric forcing have been quantified and analyzed based on NSDIC SIC dataset and ECMWF ERA-Interim dataset from 1979 to 2017. The sea ice starts to melt in early May and becomes fully frozen at the end of December. The ice melting process is much slower than freezing process. Since 2005, the lowest coverage has been nearly to be 5%, meaning the extensive ice-free condition in summer. The EOF1 patterns of SIC anomaly coincide well with the spatial patterns of trends of SIC. In winter, the whole domain almost remains unchanged and the declining trends are less than −5%/decade but with two high-value regions between −5 and −15%/decade in northwest and southwest. In summer, the sea ice area, extent and relative concentration have been declining significantly with SIC exceeding −15%/decade in the northern part. The decreasing SIC condition is closely sensitive to air temperature over sea surface with correlation coefficients between 0.5 and 1 in the whole domain. Winter accumulative temperature can significantly determine the ice regime in the following melt-freeze period. Correlation coefficients between winter accumulative temperature and melt-freeze sea ice anomaly index, duration of melt-freeze period can up to be −0.85 and 0.77, respectively. Since 2005, the summer sea ice anomaly index becomes closely related to meridional wind with correlation coefficient approaching 0.72. This sea ice motion becomes more sensitive and easily driven by the meridional strong winds when in lower SIC conditions due to the less internal ice stresses.

The Semi-implicit Cross-scale Hydroscience Integrated System Model (SCHISM), which uses unstructured grids, is set up for the North and Baltic Seas. With a resolution of ∼100 m in the narrow straits connecting the two basins, this model accurately resolves the inter-basin exchange. Validation against observations in the straits shows the model has good skill in simulating the transport and vertical profiles of temperature, salinity and currents. The timing and magnitude of the major inflow event in 2014–2015 is also realistically simulated. The analysis is focused on the two-layer exchange, its dependence on the atmospheric forcing, and dominant physical balances. The two-layer flows in the three connecting straits show different dependencies upon the net transport. The spatial variability of this dependence is also quite pronounced. The three-strait system developed specific dynamics, with time lags and differences between currents in the individual straits during inflow and outflow conditions. Analysis on the impact of resolution indicates that the performance of the model changes depending on whether the narrow parts of the straits are resolved with a resolution of 500 m or 100 m. With this ultra-fine resolution, gravity flows and variability of salinity in deep layers is generally more adequately simulated. This paper identifies the needs for more profound analysis of the coupled dynamics of Baltic and North Seas with a focus on the Danish straits.

Antinioti is a shallow Mediterranean coastal lagoon located on the island of Corfu in West Greece. For several years, the lagoon has been exploited for fish stocks by the local community. Therefore, the lagoon presents regional economic importance. However, studies on the physical, chemical, and biological properties of the lagoon are limited. Our study evaluates the effect of physical and chemical parameters on the zooplankton dynamics of Antinioti lagoon and establishes a reference for the level of biodiversity in terms of zooplankton. This initial biodiversity record will be useful in the case of a natural disaster (i.e. earthquake, tsunami, etc.) for the effective management, protection, and conservation of the lagoon. The lagoon was sampled between October 2020 and March 2021 to evaluate the correlation between physical and chemical parameters and zooplankton. Temperature and Salinity showed a significant positive correlation and BOD 5 a significant negative correlation to zooplankton. The shallow lagoon’s zooplankton community and sustainability are therefore considered to be influenced by the seawater–freshwater fluctuations that are caused by atmospheric forcing (rainfall), tides, and river runoff.

The sensitivity of different atmospheric forcing on the simulation of Sea Surface Temperature (SST) in the Indian Ocean is examined using Regional Ocean Modeling System (ROMS). Model simulations using three different atmospheric forcings from the National Centers for Environmental Prediction (NCEP; 2.5 deg), National Centre for Medium Range Weather Forecasting (NCMRWF; 0.25 deg) and TropFlux (0.5 deg) are analyzed here. Model sensitivity to the atmospheric forcing is studied by analyzing the response of SST and mixed layer depth (MLD) using statistical methods. Results show that the response of NCMRWF and TropFlux forcing was almost similar in capturing the variability of SST in comparison with the corresponding observations. But NCEP was unable to capture SST variability, especially over the central part of the Arabian Sea (AS). It is shown that deeper MLD simulations by NCEP forcing due to the high magnitude of wind resulted in an unrealistic simulation of SST.

Global satellite sea surface temperature (SST) measurements and NCEP/NCAR reanalysis wind data for the period of 1982–2009 have been used to study the seasonal and interannual variability of the main climatic oceanic frontal zones (OFZ; subpolar, subtropical and equatorial) associated with the large-scale atmospheric forcing. The seasonal variability of the OFZ is manifested in variations of their intensity (magnitude of the meridional gradient of SST) and latitudinal position of the cores (defined as areas of maximum SST gradient). The maximum intensity of the subpolar OFZ is observed in summer of the corresponding hemisphere, while subtropical OFZ are intensified synchronously in both hemispheres during boreal winter. Subtropical OFZ cores in both hemispheres shift synchronously to the south/north during the winter/summer of the Northern hemisphere, which is caused by the seasonal meridional migration of the areas of the maximum convergence of Ekman transport. All subpolar and subtropical OFZ reveal a pronounced quasi-decadal (7–10 years) variability, manifested in the variations of their intensity and latitudinal position of the zones’ cores. Strengthening of the SST gradient is accompanied by a displacement of the zones’ cores to the north in both hemispheres for subpolar OFZ, while subtropical OFZ cores migrate to the poles in this situation. Positive correlations between the maximum magnitude of the meridional gradient of zonally averaged SST and meridional shear of zonal wind (which is an estimate of the Ekman convergence intensity) were found for all subpolar and subtropical OFZ. Variability of the latitudinal position of subpolar OFZ cores is associated with the Ekman advection variability due to zonal wind variations (strengthening of zonal wind results in a shift of subpolar OFZ cores to the south/north in the Northern/Southern hemispheres). A period of the variability of the North Pacific equatorial OFZ is 4–5 years and is determined by the variability of the ENSO system. During the El Nino events, the sharp decrease of the intensity of the equatorial OFZ take place.

Extreme sea levels in the Baltic Sea are usually analyzed from tide-gauge data covering more or less extended periods. More comprehensive spatial or systematic analyses are less frequently available. Data from a high-resolution tide-surge model driven by high-resolution reanalyzed atmospheric fields reconstructing Baltic Sea sea levels from 1948 to 2011 on an hourly basis are analyzed. Meteorologically induced sea levels are characterized by pronounced annual to decadal fluctuations and a typical seasonal distribution comparable to the variability in regional wind climate. No substantial long-term trends over the considered period could be detected. Wind set-up represents the most dominant factor, however, short term variations in the filling levels of the basin and seiches contributed substantially to some of the observed peak water levels in the past. For the tide-gauge Wismar at the German Baltic Sea coast, it is exemplarily demonstrated that storm surges during periods with and without high filling levels occurred at about equal shares. When high filling levels were present, lower wind speeds were generally needed to sustain comparable peak water levels. Seiches also contributed to some of the observed extremes usually with a preferred phase shift. For Wismar, in about one third of the cases contribution from seiches at peak water level was found to exceed 10 cm.

Climate change and increased coastal urbanization are causing low-lying coastlines to become increasingly susceptible to the threat of extreme water levels and coastal flooding. Robust decision-making on adaptation in the coastal zone, based on reliable ocean-modelling tools, is therefore crucially contingent on accurate assessments of current and future storm surge hazards. This accuracy relies considerably on the quality of the wind forcing used in the ocean models. In this paper, we use a high-resolution, regional 3D ocean model (HBM) covering the North Sea and Baltic Sea to simulate extreme water levels during three extreme storm surge events with different dynamics and patterns, in order to assess their impacts along Denmark’s coastlines, which are of varying levels of complexity. We demonstrate that the model is able to reproduce the observed extreme high-water levels accurately, indicating that the system is well suited for producing simulations of present and future projections of extreme storm surges with high resulting impacts and damage potentials. Additionally, we quantify the level at which acknowledged deficiencies in the otherwise most suitable atmospheric forcing data set influence the results of the storm surge simulations. We found that reducing the temporal resolution of the forcing data – that is, replacing two out of every six time stamps with linearly interpolated values – is preferable to using the original forcing data set when recurring noise is present in these time stamps. As a result, for given storm surge events, and depending on the stage reached in the storm’s evolution, mean absolute errors can be reduced by 4.5 cm. This emphasizes the importance of considering such model fluctuations when coupling high-resolution atmosphere and ocean models.

Aerosol optical and radiative properties, measured with the ground based sun-sky radiometer (under AERONET), were explored at Kanpur in the central and Gandhi College (Ballia) in the Eastern Indo-Gangetic Plain (IGP) in Northern India during January to July 2019 (non-lockdown) and 2020 (lockdown). This year 2020 is marked an overall reduction of 15.79% and 3.39% in aerosol optical depth (AOD) than year 2019 at Kanpur and Gandhi College respectively. Lockdown 1 (23rd March to 14th April 2020) showed a reduction of 52.52% and 42.22% in AOD compared to pre-lockdown condition at Kanpur and Gandhi College respectively. Higher values of angstrom exponent measured at Eastern region (1.13 ± 0.17) than central region (0.97 ± 0.26) indicating the dominance of fine particles at Gandhi College. There was an overall reduction of 1.31% in single scattering albedo (SSA) at Kanpur while 4.34% reduction was observed at Gandhi College in year 2020 than 2019. The resultant atmospheric forcing and heating rate shows 11.86% reduction at Kanpur while 35.27% increase at Gandhi College during the lockdown period in 2020 compared to 2019. However, these values were found to decrease by 23.48% and 15.07% at Kanpur and Gandhi College respectively during the strict lockdown period compared to year 2019.

NCEP/NCAR reanalysis data for the period of 1948–2017 were used to study the multidecadal variability of the hydrometeorological parameters (thermal, dynamic and humidity) in the Caspian Sea region. Polynomial approximations of the time series of the annual mean values indicated the non-linear nature and periodicity of the long-term variability of considered parameters. Three temporal intervals of duration 10–25 years with multidirectional trends of parameters changes are detected, which is considered as a manifestation of multidecadal variability. The North-Eastern wind regime prevails over the sea basin, with the major portion of heat advection into the region provided by zonal (Eastern) transport. Phases of air warming/cooling coincide with a weakening/strengthening of the Eastern wind transport. The time lag between the shift of dynamic and thermal (as well as humidity) regimes is about 6–8 years suggesting a leading role of the large-scale atmospheric forcing variations in the regional variability of thermal and humidity parameters. Specific humidity is positively correlated with air temperature and decreases/increases during periods of cooling/warming. In contrast, relative humidity and precipitation rate variations are negatively correlated with air temperature trends. Intensification of Eastern transport and associated cooling over the Caspian Sea coincide with a situation when the North Atlantic Oscillation (NAO) index decreases to negative values, and the East Atlantic-West Russian pattern (EAWR) index is significantly positive. On the contrary, weakening of the Eastern transport and warming occur during a period of sharp strengthening of the NAO, coinciding with strongly negative values of the EAWR index.

A numerical simulation using the Regional Ocean Modeling System (ROMS) indicates that there was significant interannual-to-interpentadal variability of along-shelf transport and water properties over the Middle Atlantic Bight (MAB) from 2004 to 2013. To examine the relative contribution from local atmospheric forcing versus remote oceanic open boundary forcing to such low-frequency variability, we implement a suite of process oriented numerical experiments. Results show that the interannual variability is dominated by remote forcing from the open boundaries of the region rather than by local atmospheric forcing. The penetration of the Labrador Current into the region contributes to a significant increase of along-shelf transport in the winters of 2009 and 2010. By contrast, the anti-cyclonic mesoscale eddies associated with the Gulf Stream decrease the background along-shelf jet and, in certain cases, even reverse the along-shelf transport. In addition, the along-shelf transport appears to possess an interpentadal variation, i.e., weaker during 2004–2008 but stronger during 2009–2013, which is found caused by the migration of the Gulf Stream.

We quantify differences in ocean model simulations derived solely from atmospheric uncertainties and investigate how they relate to overall model errors as inferred from comparisons with data. For this purpose, we use a global configuration of the MITgcm to simulate 4 ocean solutions for 2000–2009 using 4 reanalysis products (JRA-25, MERRA, CFSR and ERA-Interim) as atmospheric forcing. The simulations are compared against observations and against each other for selected variables (temperature, sea-level, sea-ice, streamfunctions, meridional heat and freshwater transports). Forcing-induced differences are comparable in magnitude to model-observation misfits for most near-surface variables in the tropics and sub-tropics, but typically smaller at higher latitudes and polar regions. Forcing-derived differences are expectedly largest near the surface and mostly limited to the upper 1000 m but can also be seen as deep as 4000 m, especially in regions of deep water formation. Errors are not necessarily local in nature and can be advected to different basins. Results indicate that while forcing adjustments might suffice in optimization procedures of near-surface fields and at low-to-mid latitudes, other control parameters are likely needed elsewhere. Forcing-induced differences can be dominated by large spatial scales and specific time scales (e.g. annual), and thus appropriate error covariances in space and time need to be considered in optimization methodologies.

This study investigates the chemical composition of PM 10 aerosols at Varanasi, in the central Indo-Gangetic Plain (IGP) during April to July 2011, with emphasis on examining the contribution of elemental carbon (EC) to the estimates of direct aerosol radiative effect (DARE). PM 10 samples are analysed for carbonaceous aerosols (Organic Carbon, OC and EC) and water-soluble ionic species (WSIS: Cl − , SO 4 2− , NO 3 − , PO 4 2− NH 4 + , Na + , K + , Mg 2+ and Ca 2+ ) and several diagnostic ratios (OC/EC, K + /EC, etc) have been also used for studying the aerosol sources at Varanasi. PM 10 mass concentration varies between 53 and 310 μg m −3 (mean of 168 ± 73 μg m −3 ), which is much higher than the National and International air quality standards. The OC mass concentration varies from 6 μg m −3 to 24 μg m −3 (mean of 12 ± 5 μg m −3 ; 7% of PM 10 mass), whereas EC ranges between 1.0 and 14.3 μg m −3 (4.4 ± 3.9 μg m −3 ; ∼3% of PM 10 mass). The relative low OC/EC of 3.9 ± 2.0 and strong correlation (R 2 = 0.82) between them suggest the dominance of primary carbonaceous aerosols. The contribution of WSIS to PM 10 is found to be ∼12%, out of which ∼57% and 43% are anions and cations, respectively. The composite DARE estimates via SBDART model reveal significant radiative effect and atmospheric heating rates (0.9–2.3 K day −1 ). Although the EC contributes only ∼3% to the PM 10 mass, its contribution to the surface and atmospheric forcing is significantly high (37–63% and 54–77%, respectively), thus playing a major role in climate implications over Varanasi.

Natural and artificial systems containing water resources that have different salinities can be used to generate salinity-gradient energy (SGE). In this paper, the feasibility of implementing SGE in hypersaline coastal lagoons is addressed, taking the coastal lagoon La Carbonera in Yucatan, Mexico, as an exemplary case. A realistic approach to the exploitation conditions and potential that could occur in a SGE plant in these ecosystems is presented. We first analyzed the variability of salinity and temperature in the three characteristic zones of the coastal lagoon and the correlation of these variables with atmospheric forcing. This was done using 1 year records of in situ measurements. Then the theoretical potential for SGE and the intra-annual variability of that potential were assessed considering the three possible harvesting configurations of mixing among fresh, sea, and hypersaline water. Results show that the thermohaline structure may vary significantly for the three locations at different time scales (diurnal to seasonal) depending on the tides, winds, air temperature, atmospheric pressure, and solar radiation. That suggests that the highest annual energy yield would be obtained from alternating throughout the year among the mixing configurations, depending on the specific seasonal thermohaline structure of the lagoon.

The main objective of this study is to investigate the variability of the thermohaline characteristics of the deep-water masses in the Aegean Sea and the possible impact of the regional atmospheric forcing variability by analyzing the available oceanographic and atmospheric datasets for the period of 1960–2012. During this period the variability of the deep water characteristics of the Aegean sub-basins is found to be very large as well as the diversity of the deep water characteristics among the sub-basins. The Central Aegean seems to play the key role in the Aegean deep water formation processes. Due to its small size, the Aegean Sea surface responds rapidly to the meteorological changes and/or the variability of the lateral fluxes and this variability propagates in the thermohaline characteristics of the deep water masses of the basin through deep water formation processes. There are many episodes characterized by a tight coupling of the atmosphere and the ocean during the examined period, with the Eastern Mediterranean Transient (EMT) being the most prominent case. We suggest that deep water formation is triggered mostly by the combination of preconditioning during early winter and/or previous winters together with the number of subsequent extreme events during present winter and not only by the total amount of the extreme heat loss winter days.

Advection of anthropogenic aerosols from the Indo-Gangetic Plain (IGP) and dust aerosols from distant deserts towards a high-altitude station Merak, in the trans-Himalayan region are reported during June eJuly 2011. In order to differentiate the advection event, aerosol optical properties were examined during aged background conditions at the site. During the aged background conditions, aerosol optical depth (AOD at 500 nm) and Angstrom exponent (a) at the station were ~0.06 and 1.36, respectively which were increased to 0.13 and 1.62, respectively during the advection event. Further, a strong signature of finemode aerosol volume size distribution, dominated by absorbing aerosols, was observed during the advection event. The average atmospheric forcing during the aged background condition was found to be 0.57 Wm

We propose a new framework for parameterization of ocean convection processes. The new framework is termed “patchy convection” since our aim is to represent the heterogeneity of mixing processes that take place within the horizontal scope of a grid cell. We focus on applying this new scheme to represent the effect of pre-conditioning for deep convection by subgrid scale eddy variability. The new parameterization separates the grid-cell into two regions of different stratification, applies convective mixing separately to each region, and then recombines the density profile to produce the grid-cell mean density profile. The scheme depends on two parameters: the areal fraction of the vertically-mixed region within the horizontal grid cell, and the density difference between the mean and the unstratified profiles at the surface. We parameterize this density difference in terms of an unresolved eddy kinetic energy. We illustrate the patchy parameterization using a 1D idealized convection case before evaluating the scheme in two different global ocean-ice simulations with prescribed atmospheric forcing; (i) diagnosed eddy velocity field applied only in the Labrador Sea (ii) diagnosed global eddy velocity field. The global simulation results indicate that the patchy convection scheme improves the warm biases in the deep Atlantic Ocean and Southern Ocean. This proof-of-concept study is a first step in developing the patchy parameterization scheme, which will be extended in future to use a prognostic eddy field as well as to parameterize convection due to under-ice brine rejection.

The effect of the high frequency (synoptic) variability of wind and heat fluxes upon the surface ocean off south-central Chile (west coast of South America) is investigated using a regional ocean model. We focus our analysis in austral summer, when the regional wind experiences significant day-to-day variability superimposed on a mean, upwelling favorable flow. To evaluate the nature and magnitude of these effects, we performed three identical simulations except for the surface forcing: the climatological run, with long-term monthly mean wind-stresses and heat fluxes; the wind-synoptic run, with daily wind stresses and climatological heat fluxes; and the full-synoptic run, with daily wind-stresses and daily fluxes. The mean currents and surface geostrophic EKE fields show no major differences between simulations, and agree well with those observed in this ocean area. Nevertheless, substantially more ageostrophic EKE is found in the simulations which include synoptic variability of wind-stresses, impacting the total surface EKE and diffusivities, particularly south of Punta Lavapie (37° S), where the lack of major currents implies low levels of geostrophic EKE. Summer mean SSTs are similar in all simulations and agree with observations, but SST variability along the coast is larger in the runs including wind-stress synoptic variability, suggesting a rather linear response of the ocean to cycles of southerly wind strengthening and relaxation. We found that coastal SST variability does not change significantly in the first tenths of kilometers from the shore when including daily heat fluxes, highlighting the prominent role of wind-driven upwelling cycles. In contrast, in the offshore region situated beyond the 50 km coastal strip, it is necessary to include synoptic variability in the heat fluxes to account for a realistic SST variability.

High-resolution reanalysis of heat transport in the northwestern Pacific marginal seas was conducted for the period January 1980–December 2009 using ensemble Kalman filter. An ocean circulation model with a grid of 0.1 × 0.1° horizontal resolution and 20 vertical levels was used. Atmospheric forcing data from daily European Centre for Medium-Range Weather Forecasts were used in the ocean model. The assimilated data for the reanalysis were based on available observations of hydrographic profiles, including field surveys and Argo float and satellite-observed sea-surface temperature data. This study focused on mean and temporal variations in oceanic heat transport within the major straits among the marginal seas over 30 years. The mean heat transport in the Korea/Tsushima Strait and onshore transport across the shelf break in the East China Sea (ECS), Taiwan Strait, Tsugaru Strait, and Soya Strait were 182, 123, 82, 100, and 34 × 1012 W, respectively. The long-term trends in heat transport through the Korea/Tsushima Strait and Tsugaru Strait and onshore transport across the shelf break of the ECS were increasing, whereas the trend in heat transport through the Taiwan Strait was decreasing. There was little long-term change in heat transport in the Soya Strait. These long-term changes in heat transport through the Korea/Tsushima Strait, across the shelf of the ECS, and through the Taiwan Strait may be related to increased northeasterly wind stress in the ECS, which drives Ekman transport onto the shelf across the shelf break.

National Science Council (Taiwan) [NSC 98-2611-M-001-003, NSC 98-2621-M-002005, NSC 99-2611-M-001-005, NSC 99-2628-M-001-006, NSC 100-2628-M-001-008-MY4]; thematic program Atmospheric Forcing on Ocean Biogeochemistry (AFOBi); Drunken Moon Lake Scientific Integrated Scientific Research Platform" of Academia Sinica

The ICES subdivisions in the North Sea (SD IIIa, SD IVa, and SD IVb) and the subdivisions in the Baltic Sea (SD 29, SD 27/28-2, and SD 25/26) are selected to compare the response in long term monitoring data (1970–2000) with respect to climate regime shifts. A modified AMOEBA model is applied to the data sets to identify the status and development of the North Sea and Baltic Sea system during two recent regime shifts. Biological regime shifts can be identified 1989/1990 in SD IIIa in the North Sea and in SD 25/26 in the Baltic Sea. A synchronous appearance of regime shifts could only be identified in the central and southern Baltic Sea for both regime shifts 1975/76 and 1989/90 where the AMOEBA model indicated a high similarity in ecosystem response. A clear difference was identified in the response of the North Sea and the Baltic Sea. Inter-annual and inter-decadal variability as well as regime shifts are driven in the Baltic Sea by direct atmospheric forcing only. In contrast, the changes in the North Sea are influenced by both the direct atmospheric forcing and the indirect forcing from the changes in North Atlantic. The fact that regime shifts as well as their synchronous appearance can be identified with the AMOEBA model might be of major interest for the management of sustainable use of ecosystem goods and services, the development of ecosystem approach to management and the implementation of the Marine Strategy Framework Directive (MSFD) of the European Union (EU).

The study of aerosol optical and radiative properties presented here focuses on a geographic region in which there exist significant gaps in our knowledge. These properties have been analyzed through the ground-based Aerosol Robotic Network (AERONET) over the two megacities of Lahore and Karachi for summer (April–June) and winter (December–February) of 2010–11. During the study period the monthly mean aerosol optical depth (AOD) at 500 nm over Lahore ranged from 0.57 ± 0.18 to 0.76 ± 0.38, and the monthly mean Angstrom exponent ( ) ranged from 0.39 ± 0.17 to 1.22 ± 0.13. Likewise, over Karachi the monthly mean AOD ranged from 0.33 ± 0.11 to 0.63 ± 0.28 and the values varied between 0.29 ± 0.08 to 0.95 ± 0.22. The average AOD values in summer and winter are 0.66 ± 0.30, 0.50 ± 0.18 and 0.67 ± 0.40, 0.34 ± 0.12 in Lahore and Karachi respectively. The relationship between the Absorption Angstrom Exponent (AAE) and the Extinction Angstrom Exponent (EAE) provided an indication of the relative proportions of urban-industrial and mineral dust aerosols over the two sites. The volume size distributions were higher over Lahore than over Karachi during both seasons. The single scattering albedo (SSA) ranged from 0.83 ± 0.02 (440 nm) to 0.91 ± 0.05 (1020 nm) over Lahore and from 0.88 ± 0.02 (440 nm) to 0.97 ± 0.01 (1020 nm) over Karachi. The lower SSA values over Lahore suggest that absorbing aerosols are more dominant over Lahore than over Karachi. The average aerosol radiative forcing (ARF) values in summer at the surface and the top of atmosphere (TOA) are −101.6 ± 8.2, −63.3 ± 9.5 and −19 ± 4.35, −20 ± 3.1 over Lahore and Karachi respectively. Likewise, the average ARF values in winter at the surface and TOA are −90.3 ± 21.03, −57 ± 6.35 and −26 ± 7, −16 ± 2.3 over Lahore and Karachi respectively. The averaged aerosol ARF values over Lahore and Karachi for the entire period covered by the observations were −22.5 ± 5.9 W m−2 and −18 ± 2.2 W m−2 at the TOA and −96 ± 13 W m−2 and −60 ± 6.8 W m−2 at the surface, respectively, giving an averaged atmospheric forcing of 74.56 ± 16.8 W m−2 over Lahore and 41.85 ± 6.4 W m−2 over Karachi, which indicates significant heating of the atmosphere at both sites. The average heating rate during summer was 2.3 ± 0.1 and 1.2 ± 0.2 K day−1 and during winter was 1.8 ± 0.4 and 1.1 ± 0.1 K day−1 over Lahore and Karachi respectively.

To investigate the sub-daily variation in Tropical Easterly Jet (TEJ), a few special experiments have been conducted with mesosphere–stratosphere–troposphere (MST) radar located at Gadanki(13.5°N, 79.2°E) under Study on Atmospheric Forcing and Responses (SAFAR) campaign during 2008–2009. Large sub-daily changes in the TEJ characteristics are observed within a day in addition to day-to-day changes. Based on this observational study, three possible mechanisms for the sub-daily variations are proposed i.e., (1) motion of TEJ core, (2) large updrafts and downdrafts, and (3) strong wave activity. Interestingly, TEJ peak altitude is seen above the Cold Point Tropopause altitude for about 42% of the days.

From the 1920s to the 1940s, the Artic experienced significant warming that is comparable to the recent 30-year warming. The former warming was concentrated mostly in high latitudes, in contrast to the recent 30-year warming, which has occurred in all latitudes. Several explanations have been proposed; however, one of these proposed explanations, single external forcing, which could once explain the global average, failed to explain the early 20th century scenario. A second possible explanation was internal atmospheric variability with low frequency. Another candidate for the explanation was still forcing by black carbon deposited on snow and ice surfaces. The answer is most likely to be a combination of intrinsic internal natural climate variability and positive feedbacks that amplified the radiative and atmospheric forcing. We must continue our study by discovering historical data, analyzing ice cores, reanalyzing the Arctic system together with long-term reanalysis dating back to the 1880s, and also determine the contributions of each factor.

International audience; The Mediterranean basin features a semi-enclosed sea, where interactions and feedbacks between the atmosphere and the Sea at various temporal and spatial scales play a predominant role in the regional climate. This study analyzes the Mediterranean Sea response in sensitivity experiments conducted by driving the NEMO-MED12 oceanic model in perpetual mode with various atmospheric forcings, all produced by the WRF non-hydrostatic mesoscale atmospheric model, but differing by their resolutions : two horizontal resolutions (20 km at basin scale and 6.7 km in the North-Western [NWE] area) and two temporal resolutions (daily and three-hourly). The atmospheric fields available from August 1998 to July 1999 are in good agreement with estimates derived from satellite data. The heat budget of the Mediterranean Sea represents an heat loss of 5 W/m2 and the annual freshwater budget is -1.04 m, in agreement with climatologies. An increase in the spatial resolution in the NWE area modifies the modeled circulation from -10% to +15% for the SST, from -30% to +50% for the SSS, from -10% to +30% for the MLD and from -10% to +30% for the EKE in surface. The increase in the wind speed with a better chanelling by the land orography enhances in particular the oceanic convection process in the NWE area. On the other hand, the increase in the temporal resolution reduces the convection process, because of the diurnal restratification of the oceanic upper layer. It also reduces the surface parameters high-frequency variability, whereas it increases the EKE values in surface, due to the rapid response to the wind.

A pool of less saline surface waters was observed in late June 2006 at the northern edge of the South Adriatic Pit (SAP). Three possible sources were considered: (1) Albanian rivers, (2) local Croatian rivers, or (3) relatively fresh West Adriatic Current (WAC) waters. Available CTD and ADCP data, together with satellite images, indicate that WAC waters are the most likely source. This requires an excursion of WAC water across the width of the Adriatic and is especially surprising as low winds and stable atmospheric conditions prevailed in mid/late June. However, quite strong NNW winds occurred during the first 12 days of June, with peak winds close to the western shore. These winds were the result of the translation of the Azorean high to the British Isles, producing strong pressure gradients over the Adriatic. The winds enhanced the WAC during early June 2006, preconditioning a cross-basin eddy circulation that appeared during the wind relaxation and calm conditions. As the unusually calm conditions persisted for more than two weeks, the WAC eddies and filaments grew freely and had enough time to reach middle east-Adriatic waters. Navy Coastal Ocean Model (NCOM) simulations, using high-resolution Adriatic bathymetry and realistic atmospheric forcing, show that such excursions are plausible and can occur when eddies and instabilities push WAC waters across the hyperbolic flow point separating the WAC and Eastern Adriatic Current near the Palagruža Sill. During the latter half of June 2006, NCOM simulations show that the hyperbolic point was particularly well formed as an anticyclonic WAC, a cyclonic SAP rim flow, an anticyclonic cell southeast of Lastovo Island, and a cyclonic cell over the centre of the Palagruža Sill all bordered on each other. A simplified channel model suggests that the presence of the escarpment is a critical factor for producing cross-basin exchange of the coastal current following the relaxation of strong winds with a cyclonic wind stress curl. However, the introduction of the Gargano Peninsula in the simulations was critical to the production of mesoscale eddies in the exchange flow, and such eddies qualitatively agree with the convoluted structures observed in satellite images.

International audience; Sea level time series derived from TOPEX altimeter and from tide gauge measurements in the Bay of Biscay (Eastern North Atlantic Ocean) are used to investigate the regional sea level rise. Altimetry sea level anomalies are computed from TOPEX measurements and resampled into fixed along track bins in order to obtain consistent records and to approach as close as possible to the coast. Tidal corrections are critical in the estimation of sea level trends; therefore an additional analysis has been carried out in order to identify and correct for residual tidal signals. The obtained mean sea level rise in the region is + 3.09 ± 0.21 mm/year over the period 1993–2002. Tide gauges have been corrected for vertical land motions by means of collocated GPS measurements. GPS-corrected tide gauges and nearby altimetry trends are found to be statistically consistent. The relationship with the atmospheric forcing is also investigated revealing that 15% of this sea level rise is attributed to the atmospheric pressure effects.

Sea level variability in the Mediterranean Sea is dominated at meso- and synoptic scales by meteorologically induced motion except, in some regions where tidal resonance occurs. One such region is the Gulf of Gabes where tidal amplitudes can reach 1 m during spring tides. Sea level fluctuations were recorded at four stations around the Gulf of Gabes, during 86 days in 2003 and at three stations, within the Boughrara lagoon in the southern Gulf, during about 30 days in 1999. Spectral analysis reveals that tides are responsible for most of the variance found in sea level fluctuations. Harmonic analysis results are discussed and amplitude and phase estimates for the four major constituents (K1, O1, M2, and S2) are compared to estimates from previous studies. Based on simple dynamical arguments, it is shown that the Gulf of Gabes has the right dimensions to entertain tidal resonance for most semi-diurnal tidal harmonics. The low-frequency sea level fluctuations are finally described in relation to atmospheric forcing. They are spatially coherent and respond to both easterly winds at periods near 6.5 and 14 days and as an inverse barometer at periods close to 4–6 days.

This is the second part of a study of open boundary conditions (OBCs) in a limited-area high resolution coastal model off Oregon. In this paper, the OBCs developed in Part 1 [Ocean Modeling, 2005] are further evaluated by an application in which the coastal ocean model is forced with time- and space-dependent wind fields from a regional mesoscale atmospheric model [Journal of Geophysical Research––Oceans 107 (2002)]. The response during summer 1999 of the wind-driven upwelling flow field over the variable shelf bottom topography off Oregon coast is described. Satisfactory performance of the model and of the OBCs in this experiment with complex spatially and temporally varying atmospheric forcing is indicated by the production of physically reasonable fields in the ocean variables and by favorable model/data comparisons. Additional experiments forced by realistic, time-variable, but spatially uniform winds are included to allow a direct comparison of solutions obtained with OBCs and with cyclic boundary condition (CBCs). The general similarity of the results in these two cases provides additional support for the effectiveness of the OBCs in integrating the outer fluxes into, and radiating coastal trapped waves and advective disturbances out of, the computational domain.

Mean temporal circulation at Ormen Lange (OL) off mid-Norway is strongly dominated by the Norwegian Atlantic Current. Tidal effects are weak. Observed events of short peak value in current speed along with peak in temperature close to the seabed at the shelf slope may be driven by strong pressure gradients. That is, strong atmospheric low pressures and/or internal pressure fronts between warmer Atlantic Water (AW) and colder Norwegian Sea Water (NSW). Along the shelf slope at OL there may be steepening of the isopycnals, separating AW and NSW, due to wind generated downwelling and strong Ekman veering during storms or approaching internal density fronts. During such events the density surfaces tend to undershoot their equilibrium level, and as the forcing weakens, the suppressed water may run up along the shelf slope. In this run up phase, peak values in the velocities are often found. Since the atmospheric forcing may be a major forcing mechanism behind the observed events, we have performed a numerical study of the sensitivity of near bottom velocities at OL to the pathway of low pressure disturbances and the strength and the radii of them. The results indicate how depth dependent currents at different locations respond to varying atmospheric forcing, with highest currents close to the surface, time delay of response at greater depths and highest impact of storms passing further out in the Nordic Seas than immediately over OL.

This project examines the role of local atmospheric forcing during the transition from relatively cold wintertime to relatively warmer springtime temperatures in the northern Middle Atlantic Bight (MAB) region during 1965–1973. A one-dimensional water column model is run for eight consecutive winter seasons with local surface heat flux used as the only external forcing. Historical data from the Nantucket Light Ship, along with modeled radiation estimates for New York and Boston are used for the heat flux calculations. Two model simulations were made for each winter season, allowing for both a qualitative and quantitative comparison of model output with observed regional temperature variability and with observed temperature changes measured at Nantucket Lightship (NLS). Interannual variability (IAV) in local atmospheric heat flux during wintertime is shown to be a dominant factor in determining springtime temperature conditions during the study period. However, the residuals from a regression analysis suggest that advective processes may have contributed to the observed temperature variability, although it is believed that the advective influence is secondary to local surface heat flux in the northern MAB for this study period.

The development of the strongest El Nino event on record in the equatorial Pacific in 1997–1998 and the rapid transition to strong La Nina conditions in 1998–1999 had a large impact on the physical and biological environment of the West Coast. We investigate the evolution of the physical structure and circulation dynamics of the southern California Current System (CCS) during this period based on hydrographic data collected on 25 cruises over a 45-month period (February 1996–October 1999). The El Nino period was characterized by a significant increase in dynamic height, extreme water mass characteristics, a strengthening and broadening of the poleward nearshore flow, and a temporary reversal of net alongshore transport. By early 1999, conditions in the CCS had reversed. The data suggest that remotely driven forcing (propagating oceanic waves) contributed to the anomalies observed during the El Nino period, while the cool-water conditions of 1999 were most likely a result of anomalous local atmospheric forcing.

During the last 15 years, the knowledge of Mediterranean physical dynamics as well as of atmospheric forcing underwent a tremendous improvement because of the action within several international programs and the development of remote sensing and modelling approaches. Curiously, it is still very difficult to build up a climatological database for chemical and basic biological parameters for the whole basin because most of the data published in the open literature were preferentially related to meso- to small-scale processes. Within the European Union project Mass Transfer and Ecosystem Response (MATER), systematic measurements of routine chemical parameters, such as dissolved oxygen and nutrients, have been conducted. They will fill the existing gap between physical and chemical information. In this paper, we analyze the hydrographic data from a cruise conducted in the fall 1996 in the Central Mediterranean region and report, for the first time, on oxygen and nutrient concentrations, ranges and distributions. The joint analysis of T–S properties and chemical data also allows a better definition of water mass characteristics in this crucial area and hints at basic mechanisms relevant to water mass transformation and biological production in the basin. D 2002 Elsevier Science B.V. All rights reserved.

Solar influence on the intensity of the Indian monsoon is demonstrated using a sediment core from the eastern Arabian Sea dating back to 1200 yr, through pattern matching as well as spectral analysis of proxy records of monsoon and solar activity. The intensity of the Indian monsoon is found to have decreased during periods of solar minima during the last millennium. Periodicities of 200±20, 105±15 and 60±10 yr are observed in the proxy records coinciding with those known for solar cycles. The ∼60-yr periodicity observed in the instrumental rainfall data appears to be of solar origin and supports the hypothesis of solar control on the Indian monsoon on a multi-decadal time scale. Evidence for the presence of a coupled atmospheric forcing for the Indian and East African monsoons on a centennial time scale is also seen.

A three dimensional σ-coordinate model has been implemented for simulating the circulation in Saltfjorden, Saltstraumen and Skjerstadfjorden. The model is run with atmospheric forcing, four components of the tide at open boundaries and river runoff. The general circulation in Saltfjorden and Skjerstadfjorden and the deepwater exchange through Saltstraumen are studied. A simplified two point model is used for investigating tidal phenomena seen in the three dimensional model. Variations in air temperature and wind are shown to be a possible explanation of observed fine scale structures in the temperature profile above the thermocline in Skjerstadfjorden.

We use a hierarchy of diagnostic and prognostic numerical methods to investigate the formation mechanisms of Levantine Intermediate Water (LIW), determine the formation sites and estimate its annual formation rates. Although the three methods are different and use different hydrological/atmospheric forcing data, all of them reach the same qualitative and quantitative results: under mean climatological conditions the LIW is formed during winter in the Rhodes cyclonic gyre with an annual formation rate of 1.0 Sv. The preferred formation site is mainly controlled by the preconditioning of the hydrology, i.e., the presence of the Rhodes gyre, rather than the spatial distribution of surface forcing, which plays a significant role only during extreme meteorological episodes. The interannual variability experiments show that during severe winters, the formation rate is not increased significantly but instead, deep waters are formed in the center of the gyre, and the LIW formation area is extended towards the northeast Levantine. During mild winters, the formation rate is reduced considerably (

Resume Nous comparons les resultats d'un modele numerique aux equations primitives de la Mediterranee, force par des vents a 6h du CEPMMT, avec les mesures de topographie de surface du satellite altimetrique Topex-Poseidon en 1993. Les comparaisons montrent un bon accord qualitatif sur l'allure generale de la circulation de surface et sur un certain nombre de structures de grande echelle. Le forcage par le vent a haute frequence semble contribuer objectivement au controle de la trajectoire du modele. Les variations de transport de surface du courant Algerien et du jet medio-Mediterraneen sont en bon accord. Comme attendu, la structure des petites echelles de la circulation est cependant tres differente dans les deux cas, compte tenu de la resolution moyenne du modele (1 0 /4). Cette faible resolution est responsable d'erreurs importantes sur la reponse au forcage par le vent, le spindown des gyres saisonniers, les instabilites et meandres des courants cotiers. Cette etude permet neanmoins de servir de reference a une etape ulterieure de modelisation et d'assimilation a plus haute resolution.

The seasonal response of sea level in San Francisco Bay (SFB) to atmospheric forcing during 1980 is investigated. The relations between sea-level data from the Northern Reach, Central Bay and South Bay, and forcing by local wind stresses, sea-level pressure (SLP), runoff and the large-scale sea-level pressure field are examined in detail. The analyses show that the sea-level elevations and slopes respond to the along-shore wind stress T y at most times of the year, and to the cross-shore wind stress T x during two transition periods in spring and autumn. River runoff raises the sea-level elevation during winter. It is shown that winter precipitation in the SFB area is mainly attributed to the atmospheric circulation associated with the Aleutian Low, which transports the warm, moist air into the Bay area. A multiple linear regression model is employed to estimate the independent contributions of barometric pressure and wind stress to adjusted sea level. These calculations have a simple dynamical interpretation which confirms the importance of along-shore wind to both sea level and north-south slope within the Bay.

The purpose of this paper is to outline the pathways through which soil moisture and meteorological phenomena mutually influence one another at local, regional and global scales. This constitutes two-way land-atmosphere interaction, as meteorological phenomena both act as the forcing and react to the forcing by the soil moisture state. Land surface modification of the atmospheric environment and the atmospheric forcing of these land surface conditions from feedback loops which are significant factors in modulating the variability of the climatic system. The predictability and analysis of fluctuations and changes in regional hydrology and the atmospheric environment require an understanding of these feedback mechanisms and two-way land-atmosphere interaction. The dynamics of soil moisture at the land surface is governed by components with diverse time scales. Variability in both weather and climate are therefore influenced by the soil moisture state. In this paper, we present an overview of several studies on the mutual interaction of the soil moisture state and the atmospheric environment. We also outline possible directions for innovative investigations on the determination of soil moisture variation influences on the moist thermodynamics, energetics and dynamics of the overlying atmosphere.

The Meteorological Office processes ERS-1 fast-delivery products from the scatterometer, the altimeter, and the Along-Track Scanning Radiometer. Wind vectors, wind speed, wave height, and sea-surface temperature data are all validated against the operational atmospheric, wave, and sea-surface temperature analyses. Summary statistics from these validations are presented. The ERS-1 data appear to have smaller errors than the ship data currently used. Surface winds from the scatterometer should both improve the atmospheric analyses and forecasts, and improve the fluxes from the atmospheric analyses used to drive wave and ocean models. The wave data have made it worthwhile for the first time to develop a wave assimilation, rather than deducing the wave field solely from the history of atmospheric forcing. Results from preliminary parallel tests measuring the impact of these data sources are presented. Further work developing the model assimilation schemes is needed, before they give the full improvement hoped for.

AcknowledgementsWe would like to thank two anonymous reviewers for providing helpful comments which improved quality of the paper. Thiswork was funded by the Office of Naval Research (ONR) under the 6.1 project, Global Remote Littoral Forcing via Deep Water Path-ways, and the 6.2 project, U.S. GODAE: Global Ocean Prediction with the HYbrid Coordinate Ocean Model (HYCOM). It is also partiallysupported by grants from the Army Research Office and the National Science Foundation. The paper is contribution NRL/JA/7320/08/8254 and has been approved for public release.

The infra-red radiation thermometry done over the coastal waters off Richards Bay is described. A model concerning the local current behaviour is derived from these results as well as measurements from a research vessel. It is postulated that the atmospheric forcing of the Agulhas Current at nodal points along the South African East Coast has direct bearing on the creation of inshore turbulence and reversals regularly experienced along this coast.

All recent climatic projections for the next century suggest that we are heading towards a warmer climate than today (Intergovernmental Panel on Climate Change; Fifth Assessment Report), driven by increasing atmospheric burdens of anthropogenic greenhouse gases. In particular, the volume mixing ratio of methane, the second-most important anthropogenic greenhouse gas, has increased by a factor of ~2.5 from the beginning of the European Industrial Revolution. Due to their complex responses to climatic factors, understanding of the dynamics of future global methane emissions and sinks is crucial for the next generation of climate projections. Of relevance to this problem, the Earth likely experienced warmer average temperatures than today during the Last Interglacial (LIG) period (130-115kaBP). Interestingly, ice cores do not indicate a different methane mixing ratio from the Pre-Industrial Holocene (PIH), in other words the current interglacial period prior to anthropogenic influence. This is surprising as warmer temperatures might be expected to increase methane emissions. The present study aims to improve our understanding of the changes in the global methane budget through quantifying the relative importance of sources and sinks of methane during the last full glacial-interglacial cycle.A fairly limited number of studies have investigated this cycle at the millenium time scale with most of them examining the doubling in CH4 from the Last Glacial Maximum (LGM) to the PIH. Though it is still a matter of debate, a general consensus suggests a predominant role to the change in methane emissions from wetlands and only a limited change in the oxidising capacity of the atmosphere. In the present study we provide an estimate of the relative importance of sources and sinks during the LIG period, using a complex climate-chemistry model to quantify the sinks, and a methane emissions model included in a global land surface model, for the sources. We are not aware of any previous studies that have explicitly tackled sources and sinks of methane in the previous interglacial. Our results suggest that both emissions and sinks of methane were higher during the LIG period, relative to the PIH, resulting in similar atmospheric concentrations of methane. Our simulated change in methane lifetime is primarily driven by climate (i.e. air temperature and humidity). However, a significant part of the reduced methane lifetime is also attributable to the impact of changes in NOx emissions from lightning. An increase in biogenic emissions of non-methane volatile organic compounds during the LIG seems unlikely to have compensated for the impact of temperature and humidity. Surface methane emissions from wetlands were higher in northern latitudes due to an increase of summer temperature, whilst the change in the tropics is less certain. Simulated methane emissions are strongly sensitive to the atmospheric forcing, with most of this sensitivity related to changes in wetland extent. © 2015 Elsevier Ltd.