Archive for the ‘Climate’ Category

Sea temperatures from HMS Beagle

beaglesst

 

  • The graph shows a comparison between modern sea surface temperatures (SST) and temperatures measured during the 1831-1836 voyage of Captain Fitzroy and Charles Darwin on HMS Beagle.
  • Data collected by the Beagle were assigned to weekly buckets of a 53-week year.  Modern (1981-2017) weekly means at the ship locations were subtracted to give temperature “anomalies” experienced during the voyage.
  • The graph indicates that the Eastern Pacific ocean was anomalously cold during Darwin’s time at the Galapagos (shaded area). This looks consistent with a La Nina event.
  • Average temperatures during the voyage were 0.7°C cooler compared to an equivalent trip made today. The Beagle data are slightly more volatile compared to the modern SST dataset. This is to be expected because the latter is an average over time and space (1° x 1°) whereas the Beagle measurements were local in time and space.
  • Measurements at anchor and at interpolated coordinates are omitted.
  • HMS Beagle data derived from the ICOADS database, which is a very rich source of shipping data with all kinds of application.

 

Ocean drifters

 

drifterssouthernocean

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(),

transformed to a stereographic coordinates using spTransform()

and plot using geom_path()

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