A 70-Year Meteorological Time Series at Station Papa from an Ocean Weather Ship (1949-1981) and a NOAA Surface Mooring (2007-Present)

Abstract:

Ocean Weather Station Papa, located at 50°N 145°W, has one of the longest oceanic time series, dating from 1949 to 1981, when two ships would rotate every six weeks taking oceanic and meteorological measurements. After the weather ship program ended in 1981, oceanographic monitoring continued through regular Line-P cruises to Station Papa, while the meteorological record resumed in 2007 when a NOAA surface mooring was deployed at the same location. This study uses Station Papa’s oceanic and meteorological time series to investigate two hypotheses that might explain the surface freshening observed at Station Papa over the 70-year period. The first hypothesis is that increased rainfall, either as a result of more frequent or more intense storms, is causing the surface salinity to decrease. The second hypothesis is the atmosphere at Station P has become more moist, thus reducing evaporation (i.e. latent heat loss) and thereby contributing to the freshening of sea water observed. Climatologies computed for the mooring and for the weather ship, show that the first hypothesis is correct, while the second is not. Rainfall has increased at Station P over the last 70 years, but so has evaporation, although to a lesser extent such that the net precipitation minus evaporation is now larger than it was during the ocean weather ship era. The increase in evaporation appears to be due to the increase in sea surface temperature. This long time series allows us to better understand our changing world and can also be used to test numerical weather prediction analyses that extend back into historical times.