A big float story slipped under the HT radar a month ago. Luckily I noticed the NZ connection in a recent release from the Scripps Institute in California – designers and builders of many of the Argo float network – and so I bring you news of the completion of this ocean monitoring system and the big role played by NIWA and its research ship, the Kaharoa, in deploying the floats. Better late than never…
Oceans cover 70 percent of the earth’s surface, and have a huge influence on climate and weather patterns, so mapping how currents move heat around is a very important part of weather and climate modelling – particularly for long range and seasonal forecasting. The 3,000 Argo floats are deployed around the oceans of the world (on a roughly 3×3 degree grid), and spend most of their time floating at 1,000 to 1,500m below the surface. Every ten days, each float dives to 2,000m and then heads to the surface, measuring temperature and salinity as it rises. At the surface, the data is transmitted via satellite to ground stations for analysis, and the cycle then repeats. Each float carries enough battery power for about 150 cycles. Around 800 need replacing every year. There are also special “ice floats” which are deployed around Antarctica. They can sense the presence of ice overhead, and store data until they reach open water, or summer arrives. The “float of the month” page at the Argo Information Centre has some fascinating detail.
NIWA’s role in Argo has been to deploy floats around the Southern Ocean. The RV Kaharoa is currently on its way to Valparaiso in Chile and will launch 64 floats – including the 3,000th, which will complete the network. She holds the record for most floats launched – a quarter of all those in the southern hemisphere – and on a trip to Madagascar was boarded by pirates. Who said oceanography was dull?
Argo data, together with information from the Jason satellite sea surface height measuring system (Jason and the Argonauts, geddit?), is used to provide real time, or near real time maps of ocean characteristics which can be used as the sea-going equivalent of the balloon measurements of the atmosphere used by weather forecasters. The UK Met Office, for example, uses Argo data in its FOAM and GloSea modelling and seasonal forecasting systems. Argo data will play a key part in building better models of oceanic circulation, and those in turn will help with near term climate projections – which will play a key role in helping us to adapt to climate change as it happens.