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Large waves pose risks to ships, offshore structures, coastal infrastructure and ecosystems. This paper analyses 10 years of in-situ measurements of significant wave height (Hs) and maximum wave height (Hmax) from the ocean weather ship Polarfront in the Norwegian Sea. During the period 2000 to 2009, surface elevation was recorded every 0.59 s during sampling periods of 30 min. The Hmax observations scale linearly with Hs on average. A widely-used empirical Weibull distribution is found to estimate average values of Hmax/Hs and Hmax better than a Rayleigh distribution, but tends to underestimate both for all but the smallest waves. In this paper we propose a modified Rayleigh distribution which compensates for the heterogeneity of the observed dataset: the distribution is fitted to the whole dataset and improves the estimate of the largest waves. Over the 10-year period, the Weibull distribution approximates the observed Hs and Hmax well, and an exponential function can be used to predict the probability distribution function of the ratio Hmax/Hs. However, the Weibull distribution tends to underestimate the occurrence of extremely large values of Hs and Hmax. The persistence of Hs and Hmax in winter is also examined. Wave fields with Hs>12 m and Hmax>16 m do not last longer than 3 h. Low-to-moderate wave heights that persist for more than 12 h dominate the relationship of the wave field with the winter NAO index over 2000–2009. In contrast, the inter-annual variability of wave fields with Hs>5.5 m or Hmax>8.5 m and wave fields persisting over ~2.5 days is not associated with the winter NAO index.

Ice-edge blooms are significant features of Arctic primary production, yet have received relatively little attention. Here we combine satellite ocean colour and sea-ice data in a pan-Arctic study. Ice-edge blooms occur in all seasonally ice-covered areas and from spring to late summer, being observed in 77–89% of locations for which adequate data exist, and usually peaking within 20 days of ice retreat. They sometimes form long belts along the ice-edge (greater than 100 km), although smaller structures were also found. The bloom peak is on average more than 1 mg m−3, with major blooms more than 10 mg m−3, and is usually located close to the ice-edge, though not always. Some propagate behind the receding ice-edge over hundreds of kilometres and over several months, while others remain stationary. The strong connection between ice retreat and productivity suggests that the ongoing changes in Arctic sea-ice may have a significant impact on higher trophic levels and local fish stocks.

A repeat hydrographic section (WOCE section SR1b) across Drake Passage was occupied during December 2008 aboard the RRS James Clark Ross (JR194). This is a section across the Antarctic Circumpolar Current at its narrowest point, with the primary objective of this cruise being to determine the currents, characteristics and transports of the various water masses. A total of 32 CTD/LADCP stations were sampled across Drake Passage and down to Rothera, of which 30 comprised the SR1b repeat hydrographic section between Burdwood Bank and Elephant Island, and the first two were test stations. In addition to temperature, salinity and oxygen profiles from the sensors on the CTD package, water samples from the 24-bottle rosette were analysed for salinity at each station, in order to calibrate the CTD salinity profiles. Also, samples were collected from the shipís underway system to calibrate and complement the data continually collected by the OceanLogger. Full depth velocity measurements were made at every station by an LADCP (lowered acoustic Doppler current profiler) mounted on the frame of the rosette. Throughout the cruise, velocity data in the upper few hundred metres of the water column were collected by the shipsí VMADCP (vessel mounted acoustic Doppler current profiler) mounted on the hull. Meteorological variables were monitored using the onboard surface water and meteorological sampling system. Bathymetry data were also collected using a Simrad EA600 echo-sounder, and 7 Argo floats were deployed. A new addition to the scientific complement was the study of microbial abundance and dynamics within the Drake Passage section. Flow cytometry was used to compare the abundance of dominant microbial plankton groups, and a scintillation counter to assess the productivity rates of the bacterioplankton. The work is a component of the "Sustained Observations" supported by NERC's Oceans 2025 programme. This report describes the methods used to acquire and process the data on boa

A repeat hydrographic section (WOCE section SR1b) across Drake Passage was occupied during November and December 2007 aboard the RRS James Clark Ross (JR193). This is a section across the Antarctic Circumpolar Current at its narrowest point, with the primary objective of this cruise being to determine the currents, characteristics and transports of the various water masses. A total of 42 CTD/LADCP stations were sampled across Drake Passage and down to Rothera, of which 30 comprised the SR1b repeat hydrographic section between Burdwood Bank and Elephant Island. In addition to temperature, salinity and oxygen profiles from the sensors on the CTD package, water samples from the 24-bottle rosette were analysed for salinity at each station, in order to calibrate the CTD salinity profiles. In addition, samples were collected from the ships underway system to calibrate and complement the data continually collected by the OceanLogger. Full depth velocity measurements were made at every station by an LADCP (lowered acoustic Doppler current profiler) mounted on the frame of the rosette. Throughout the cruise, velocity data in the upper few hundred metres of the water column were collected by the ships VMADCP (vessel mounted acoustic Doppler current profiler) mounted on the hull. Meteorological variables were monitored using the onboard surface water and meteorological sampling system. Bathymetry data were also collected using a Simrad EA600 echo-sounder, and a number of ARGO floats and a surface drifter deployed. The work is a component of the "Sustained Observations" supported by NERC's Oceans 2025 programme. This report describes the methods used to acquire and process the data on board the ship during cruise JR193.

Flux products quantifying exchanges between ocean and atmosphere are needed for forcing models, understanding ocean dynamics, investigating the ocean’s role in climate, and assessing coupled models. Research experiments are essential to improve flux parameterizations, and longer research deployments are required to sample rare events. Urgently needed technological improvements include longer battery life, more robust sensors and improvement of sensors for humidity, precipitation and direct gas and particle fluxes. A range of different flux products are needed, incorporating data from ships, satellites and models in different combinations and using different methods. All products must be characterized with uncertainty estimates. Dataset validation requires high quality observations from ocean flux reference sites and from ships. The continued development of flux products from satellites provides much-needed sampling. Continual intercomparisons among products and with high quality observations will lead to improved flux datasets, while improvements to the flux data management system would facilitate these intercomparisons.

Dual-frequency rain-flagging has long been a standard part of altimetric data analysis, both for quality control of the data and for the study of rain itself, because altimeters can provide a finer spatial sampling of rain than can passive microwave instruments. However, there have been many varied implementations, using different records of the surface backscatter and different thresholds. This paper compares four different measures available for the recently-launched Jason-2. The evaluation compares these measures against clearly desired properties, finding that in most cases the adjusted backscatter and that from the ice retracker perform much better than that recommended in the users' handbook. The adjusted backscatter measure also provides a much better link to observations from Jason-1, opening up a much longer period for consistent rain investigations, and enabling greatly improved analysis of the short-scale variability of precipitation. Initial analysis shows that although the spatial and temporal gradients of backscatter increase at very low winds, the spatial gradients in rain attenuation are concentrated where rainfall is greatest, whilst the temporal changes have a simple broad latitudinal pattern.

This report describes the twelfth repeat hydrography section across Drake Passage, first established during the World Ocean Circulation Experiment. For this work NOC made use of the regular BAS supply trip to Rothera from the Falklands using the RRS James Clark Ross. Thirty CTD/LADCP stations were carried out across the 753 km section from Burdwood Bank to Elephant Island, plus one test station in the deep waters to the north of Burdwood Bank. Maximum station spacing on the section was 33 km, with stations closer together on the continental shelves. Water samples were drawn for salinity analysis, for subsequent CTD conductivity calibration. Samples were also drawn for analysis of oxygen isotope fraction δ18O, for later analysis back at NOC. The CTD was a SeaBird 911plus with dual temperature and conductivity sensors. There were two LADCP instruments, but no useful data were collected with them. Various underway measurements were also collected, including navigation, vessel-mounted ADCP, sea surface temperature and salinity, water depth and meteorological parameters. Water samples were also collected for subsequent analysis for chlorophyll, particulate carbon and biogenic silica.

The role of ocean heat transport variations in recent warming of the North Atlantic is investigated using an eddy-permitting global ocean model with prescribed atmospheric boundary conditions for 1985–2003. Variability of the model sea surface temperature compares favorably with satellite and in situ observations. Each data set reveals a similar pattern of significant surface warming over 1985–2003, across much of the North Atlantic. Significant warming trends exceed 0.1°C a−1 across a large area of the northwest Atlantic in the model simulation. Warming of the tropics and midlatitudes are considered separately. In both regions, long-term rises in temperature coincide with increasing ocean heat content in the upper few hundred meters, consistent with recent observations. The strongest link between surface temperature and heat content is found in midlatitudes. Averaged within each region, model surface heat fluxes do not show any major trends and are within the range of uncertainty in observational estimates. In midlatitudes, heat content increases are largely explained by changes in ocean heat transport across regional boundaries. While meridional heat transport is strongly linked to the meridional overturning circulation in the subtropics, such a link is weak in midlatitudes, where heat transport variability appears to be more strongly linked to fluctuations in gyre transport and eddy fluxes. It is concluded that the pattern of recent warming in the midlatitude North Atlantic is related to anomalous convergence of ocean heat transport, associated with changes in overturning and horizontal components of the circulation, in the northern subtropics and the subpolar gyre respectively.

Owing to the highly variable nature of rain both in space and time and the difficulties in obtaining accurate in situ measurements, increasing reliance is being placed on the various types of satellite data now available. The multi-sensor payload of Envisat is of particular interest because the data are co-located and simultaneous, thus reducing some of the uncertainty found in multi-platform analyses. This paper shows variations in cloud and precipitation data derived from AATSR, RA-2 and MWR-2 measurements in an overpass of Hurricane Juan, revealing significant asymmetry in the spatial distribution. The results are discussed in the context of similar data from other tropical and sub-tropical features in the western Atlantic. The combination of data from these sensors allows us to see the effects of different drop-size distribution at varying distances from the eye and to conclude that active microwave systems are needed for studying small-scale variations in rainfall.

Precipitation is a parameter that varies on many different spatial and temporal scales. Here we look at interannual variations associated with the North Atlantic Oscillation (NAO) and the Southern Oscillation (SO), comparing the spatial and temporal changes as shown by three data sets. The Global Precipitation Climatology Project (GPCP) product is based upon satellite data, whereas both the National Centers for Environmental Prediction (NCEP) and European Centre for Medium-Range Weather Forecasts (ECMWF) climatologies are produced through reanalysis of atmospheric circulation models. All three products show a consistent response to the NAO in the North Atlantic region, with negative states of the NAO corresponding to increases in precipitation over Greenland and southern Europe, but to a decrease over northern Europe. None of the climatologies display any net change in total rainfall as a result of the NAO, but rather a redistribution of precipitation patterns. However, this redistribution of rain is important because of its potential effect on oceanic overturning circulation. Similarly, all three data sets concur that the SO has a major effect on precipitation in certain tropical regions; however, there is some disagreement amongst the data sets as to the regional sensitivity, with NCEP showing a much weaker response than GPCP and ECMWF over Indonesia. The GPCP and NCEP climatologies show that the various phases of El Niño and La Niña act to redistribute, rather than enhance, the freshwater cycle. Given that the models incorporate no actual observations of rain, and are known to be imperfect, it is surprising how well they represent these interannual phenomena.

A strong but variable western boundary current flows south along the east coast of Madagascar, and at the island's southern end it interacts with eddies propagating zonally from the east. These two routes of variability are compared using altimetric sea-surface-height data and dynamic height from a high-resolution numerical model. The effects on biological productivity are also discussed.

This report presents the results of Task 6 of the study led by the Southampton Oceanography Centre under ESRIN Contract No.17900/03/I-LG in response to AO/1-4539/03/I-LG on the Exploitation of the ENVISAT Radar Altimeter Individual Echoes and S Band Data for Ocean, Coastal Zone, Land and Ice/Sea-Ice Altimetry (RAIES). This report first reviews the findings relating to scientific applications of RA2 S-band data for the ocean and the coastal zone, including improved rain, wind and wave products. Using a combination of numerical waveform simulations and comparisons with ERS2 and buoy data, the added value provided by S-band measurements to estimate range, wave height and backscatter was examined. S-band measurements over the ocean and in the coastal zone appear much noisier than Ku-band and ERS measurements when validated against SWH buoy data. However, S-band σ0 values are found to be less affected by rain than Ku-band σ0. Ionospheric corrections based on RA-2 dualfrequency data show good agreement with those obtained from the JPL Global Ionospheric Maps (GIM). Global analyses show that S-band anomalies occur globally, with slight preference over Indonesia and descent over South America, plus poles. No periodicity is evident, indicating a likely instrumental origin. A new approach to estimating sea state bias at S-band using theoretical and empirical formulations is proposed. The second part of the report presents the scientific applications with S-band data over land and ice/sea ice surfaces. Overall, the use of S-band for land/ice surfaces sounds promising. Extremely good echo retrieval is achieved at S-band over land surfaces, attributed to the width of the S band range window. Over sea ice, intriguing variations in the complex echo shapes are seen between Ku and S-band. Unexpected temporal variations are observed in many categories of waveform shape at S-band, which are not mirrored at Ku-band. This strongly indicates that the information content at S band differs

This paper presents a study of the characteristics of extra-tropical oceanic Rossby waves from datasets of Sea Surface Height (SSH), Sea Surface Temperature (SST) and ocean colour. The main focus is on the propagation speed of the waves and a comparison is made between the observational results and the speeds predicted by the classical theory and by the most recent extended theory of Rossby waves. There is also discussion, with an example, of the additional information that can be derived by a comparison of the wave signatures in the different datasets.

The existence of waves in oceanic plankton populations has been conjectured on theoretical grounds. We report the first open ocean observations of a possible plankton wave in the Indian Ocean, seen in satellite ocean colour data. The chlorophyll feature travels from west to east, in the opposite direction to the mean flow and the Rossby wave and eddy propagation direction. For the strongest observed event, in February to April 1999, the wave propagates in the latitude band ∼22–30°S away from Madagascar and dies out at ∼75°E.

The Agulhas Current system contains one of the world's strongest western boundary currents, and plays an important part in the warm water path of the global thermohaline circulation. However, there have been few surveys of the source regions of the Agulhas Current, and thus little in situ measurement of their variability. Utilizing the more than 5-year record of SeaWiFS data, we examine the eddy activity present in the southern portion of the Mozambique Channel. The two sources of Agulhas input from the central Indian Ocean (southward flow through the Mozambique Channel and westward flow around the southern limit of Madagascar) both show great temporal variability, with no clear seasonal signal. A number of large (-200 km diameter) anticyclonic rings intermittently propagate poleward along the western edge of the channel, sweeping coastal waters into mid channel. Their passage past Maputo appears to affect the circulation of the lee eddy in the Delagoa Bight. The eastern side of the channel is mainly characterized by cyclonic eddies. These are made manifest in the lee of the southern tip of Madagascar, although it is not clear whether many form there or just develop a visible presence due to entrainment of high chlorophyll coastal waters. Several of these cyclonic eddies then appear to move in west-southwesterly direction. The chlorophyll data do reveal the East Madagascar retroflection on occasions, but do not show clear examples of the pinching off of anticyclonic eddies. However surface waters from the East Madagascar Current may reach the African mainland on occasions when no retroflection is present.

TOPEX and Jason were the first two dual-frequency altimeters in space, with both operating at Ku- and C-band. Each thus gives two measurements of the normalized backscatter, sigma0, (from which wind speed is calculated) and two estimates of wave height. Departures from a well-defined relationship between the Ku- and C-band sigma0 values give an indication of rain. This paper investigates differences between the two instruments using data from Jason's verification phase. Jason's Ku-band estimates of wave height are ~1.8% less than TOPEX's, whereas its sigma0 values are higher. When these effects have been removed the root mean square (r.m.s.) mismatch between TOPEX and Jason's Ku-band observations is close to that for TOPEX's observations at its two frequencies, and the changes in sigma0 with varying wave height conditions are the same for the two altimeters. Rain flagging and quantitative estimates of rain rate are both based on the atmospheric attenuation derived from the sigma0 measurements at the two frequencies. The attenuation estimates of TOPEX and Jason agree very well, and a threshold of -0.5 dB is effective at removing the majority of spurious data records from the Jason GDRs. In the high sigma0 regime, anomalous data can be cause by processes other than rain. Consequently, for these low wind conditions, neither can reliable rain detection be based on altimetry alone, nor can a generic rain flag be expected to remove all suspect data.

Wave height can be measured as accurately from satellite altimeters as from surface buoys and data accumulated since 1985 have been used to show both that the NE Atlantic became rougher and that fluctuations in different oceans may be linked. Planetary waves are an important mechanism for carrying information across ocean basins and may modify currents such as the Gulf Stream and Kuroshio. Detection of one type (Rossby waves) from satellite measurements of sea level, sea temperature and ocean colour will be presented; the inferred characteristics have already led to revisions of standard theories with implications for the way the oceans affect climate. Although unforeseen when the sensors were designed altimeters can also be used to identify rain events. A new precipitation climatology, derived from measured backscatter intensity, will be described and compared with previous work. It has the advantage of using a single sensor-type for tropical to polar latitudes.

Recently developed algorithms have shown the potential recovery of rainfall information from spaceborne dual-frequency altimeters. Given the long mission achieved with TOPEX and the prospect of several other dual-frequency altimeters, we need to validate the altimetrically derived values so as to foster their integration with rain information from different sensors. Comparison with some alternative climatologies shows the bimonthly means for TOPEX to be low. Rather than apply a bulk correction we investigate individual rain events to understand the cause of TOPEX's underestimation. In this paper we compare TOPEX with near-simultaneous ground-based rain radars based at a number of locations, examining both the detection of rain and the quantitative values inferred. The altimeter-only algorithm is found to flag false rain events in very low wind states (<3.8 m s-1); the application of an extra test, involving the liquid water path as sensed by the microwave radiometer, removes the spurious detections. Some false detections of rain also occur at high wind speeds (>20 m s-1), where the empirical dual-frequency relationship is less well defined. In the intermediate range of wind speeds, the TOPEX detections are usually good, with the instrument picking up small-scale variations that cannot be recovered from infrared or passive microwave techniques. The magnitude of TOPEX's rain retrievals can differ by a factor of 2 from the ground-based radar, but this may reflect the uncertainties in the validation data. In general, over these individual point comparisons TOPEX values appear to exceed the “ground truth.” Taking account of all the factors affecting the comparisons, we conclude that the TOPEX climatology could be improved by, in the first instance, incorporating the radiometric test and employing a better estimate of the melting layer height. Appropriate corrections for nonuniform beam filling and drizzle fraction are harder to define globally.

This paper compares the observed ambient sound levels at two very different sites, relating both to independent estimates of wind speed and rain rate. The spectra for wind-only conditions at the two sites show great differences, especially at low wind speed. The spectra associated with rain were sufficiently different from the wind-only spectra (either in terms of spectral slope or the intensity at 14.5 kHz) to support the development of a generic rather than site-specific rain detection algorithm.