Ocean drifters



The map shows tracks of drifting buoys deployed in the southern ocean between 2005 and 2016. The underlying dataset consists of 15-minute gps data collected from 4608 buoys, available from NOAA ftp://ftp.aoml.noaa.gov/pub/phod/buoydata/. Colour indicates speed of drift.

This is simply a visualisation of the raw drifter data with no further analysis or modelling. Nevertheless all of the well-known features of the surface circulation in the southern ocean emerge; Antarctic Circumpolar Drift, western boundary currents along the western coasts of South America (Brazil Current) and Africa (Agulhas),  powerful Agulhas Return Current in the Southern Indian Ocean, South Atlantic gyre (centred NorthEast of the Falkland Islands) etc.

R code

A dataframe buoydata was created using fread(),

buoydata <- fread("../buoydata_10001_15000.dat")

transformed to a stereographic coordinates using spTransform()

antarctic <- CRS("+proj=stere +datum=WGS84")
lonlat <- CRS("+proj=longlat +datum=WGS84")
buoydata.sp <- SpatialPointsDataFrame(select(buoydata, lon,lat),data = select(buoydata,-lon,-lat),proj4string=lonlat)
buoy.df <- as.data.frame(spTransform(buoydata.sp,antarctic))

and plot using geom_path()

ggplot(buoy.df) + geom_path(aes(lon,lat,group=ID,colour=speed),alpha=0.15,size=0.2)

Note the use of transparency (alpha). This can be varied to highlight different aspects of the flow.



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