Eddies in the southern Mozambique Channel

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

RRS James Clark Ross Cruise 193, 29 Nov – 08 Dec 2007. Drake Passage repeat hydrography: WOCE Southern Repeat Section 1b – Burdwood Bank to Elephant Island.

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

Intercomparison of ambient acoustic spectra in inland and coastal waters

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

Back to basics: measuring rainfall at sea. Part 1 - in situ sensors

Rainfall is an important climatic variable. Extremes in rainfall accumulations over land - either floods or droughts - have major societal implications and are obvious. At sea, the effects on human activity are less evident, apart from the inconvenience to deck passengers on cruise liners! However, improved knowledge of the rainfall associated with weather systems approaching the UK from the Atlantic would be beneficial to weather forecasting, especially if assimilated into atmospheric models. There is an additional, more subtle, effect involving the ocean itself. At sea, the balance between precipitation and evaporation provides a critical feedback in climate change

Seeking best practice in online learning: Flexible learning toolboxes in the Australian VET sector

This paper describes The Flexible Learning Toolboxes Project , a component of the Australian Flexible Learning Framework for the National Vocational Education and Training System 2000-2004 (AFL Framework). The AFL Framework is designed to support the accelerated take-up of flexible learning modes and position Australian VET as a world leader in applying new technologies to vocational education products and services. A Toolbox is a set of learning resources designed for web based delivwww.ascilite.orgs customisation and reuse in the National Training Framework, which forms the basis of qualifications and accreditation in the Australian VET sector. The paper describes aspects of the Project and discusses the innovative design approaches that are being used to create quality online learning resources. Examples of several Toolboxes are provided to demonstrate the forms of online learning settings that have been developed for the Australian VET sector

Mozambique Channel Eddies in GCMs: A question of resolution and slippage

Hydrographic observations in the 21st century have shown that the flow within the MozambiqueChannel is best described by a series of large poleward-propagating anticyclonic eddies, rather than, aspreviously thought, a continuous intense western boundary current. The portrayal of this region in various runs of the NEMO 75-level model is found to vary between those two descriptions depending upon the resolution used and the implementation of the model's lateral boundary conditions. In a comparison of 1/4 ? resolution runs, the change of these conditions from free-slip to no-slip leads to the mean southward flow moving further offshore, with greater variability in the zonal and meridional velocities as the flow organises itself into eddies, and a reduction in total transport. If a realization of a model is unable to get these aspects of the physical flow correct, then this will significantly reduce its ability to show a realistic biological signal or long-term response to climate change. Further south, beyond Durban, the application of no-slip conditions similarly causes the mean Agulhas Current to lie further offshore, making it much more able to simulate Natal Pulses.<br/

Altimeter accuracy requirements for detecting changes in sea level rise

All nations with a maritime border are concerned about changes in sea level, with an increase in sea level leading to flooding of coastal areas, damage to property, salinification of fresh water aquifers and destruction of valuable agricultural land. Around the change of the millenium global sea level rise was estimated to be 2.7 mm/yr, but various climate models have suggested the rate of rise will increase markedly necessitating governments to take action more swiftly. This report looks briefly at the accuracy requirements and time series duration needed to be able to detect reliably a significant change in the rate of sea level rise. One constraint on detecting an increased trend is the natural interannual variability of the climate system, which implies that a minimum duration of around 10-20 years is required in order to detect a trend with confidence to within 1 mm/yr. Added to this will be the effect of efficiencies in the observing system. This is investigated through a series of simulations, mimicking the sampling of a long-time series by altimeters with random bias and drift terms. Whilst not directly addressing issues relating to the choice of orbit configuration, this preliminary work prototypes a methodology for assessing the design of a long-term altimetry observing system. Naturally the maintenance of multiple altimeter systems plus a representative global network of tide gauges provides the best basis for such monitoring. However, considering only a single system, one notes that the required dataset duration can be between 10 and 60 years depending upon the quality of the altimeter missions. Due to the difficulty of tying separate missions to a common datum, a single short interruption to precise monitoring may add more than a decade to the time required to detect an increased rate of sea level rise

RRS James Clark Ross Cruise 194, 12-23 Dec 2008. Drake Passage repeat hydrography: WOCE Southern Repeat Section 1b – Burdwood Bank to Elephant Island.

A repeat hydrographic section (WOCE section SR1b) across Drake Passage was occupiedduring December 2008 aboard the RRS James Clark Ross (JR194). This is a section across theAntarctic Circumpolar Current at its narrowest point, with the primary objective of this cruisebeing 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 andElephant Island, and the first two were test stations. In addition to temperature, salinity andoxygen profiles from the sensors on the CTD package, water samples from the 24-bottle rosettewere 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 datacontinually collected by the OceanLogger. Full depth velocity measurements were made atevery station by an LADCP (lowered acoustic Doppler current profiler) mounted on the frameof the rosette. Throughout the cruise, velocity data in the upper few hundred metres of thewater column were collected by the shipsí VMADCP (vessel mounted acoustic Doppler currentprofiler) mounted on the hull. Meteorological variables were monitored using the onboardsurface water and meteorological sampling system. Bathymetry data were also collected usinga Simrad EA600 echo-sounder, and 7 Argo floats were deployed. A new addition to thescientific complement was the study of microbial abundance and dynamics within the DrakePassage section. Flow cytometry was used to compare the abundance of dominant microbialplankton groups, and a scintillation counter to assess the productivity rates of thebacterioplankton.The work is a component of the "Sustained Observations" supported by NERC's Oceans 2025programme. This report describes the methods used to acquire and process the data on boardthe ship during cruise JR194

RRS Discovery Cruise 288, 26 Jan - 21 Feb 2005. Madagascar Experiment (MadEx)

MadEx (Madagascar Experiment) was a research cruise on RRS Discovery with the aims of i) surveying the currents south of Madagascar, ii) deploying moorings, and iii) relating the different biological communities to the physical and chemical conditions (temperature, currents and nutrients). The cruise departed from Durban on 26th January 2005, and returned there on 21st February. An eddy/retroflection signal was seen in ocean colour imagery south of Madagascar, and a "radiator grille" survey pattern adopted. This was achieved with a mixture of SeaSoar tows, CTDs and XBTs, with Jason track 196 being occupied at the time of the altimeter overflight. An array of moorings was also laid along this line, with a McLane Moored Profiler placed 120 km further east. A number of surface drifters were also deployed, including the new Pop-up Ocean Drifters. Numerous underway measurements were made. As well as the shipborne ADCPs and standard instrumentation on the non-toxic supply, surface water samples were taken typically every 2 hours to determine salinity and chlorophyll, and other samples kept for subsequent microscopic and flow cytometry analyses. For zooplankton studies, there were vertical hauls of Bongo nets at half the CTD stations. Extra biological information was provided by the Optical Plankton Counter (OPC), Fast Repetition Rate Fluorometer (FRRF) and the Turner Fluorometer, which were all working well on SeaSoar during the latter part of the cruise. MadEx II (Discovery cruise D302) recovered the moorings 14 months later, and repeated some of the biological and physical measurements along the mooring line; it is the subject of a separate cruise report