This page compares weather observations made on the Hecla with recent expected values (1961-90 normals). Observations were made on sea-temperature (SST), air-temperature (AT), and Pressure (SLP). It is also possible to infer the sea-ice cover the ship experienced and compare that to recent expected values. Both observed and comparative recent values depend both on the date (position in the seasonal cycle) and the position of the ship - here we show time-series comparisons comparing the actual observations with those which would be expected by a hypothetical ship following the same course, at the same time of year, in recent decades.
Sea temperature Observed (red dots) and modern equivalent (black line) sea-surface temperatures.
The lower graph shows the range in expected sea-ice coverage - max and
min values from HadISST for 1961-90.
Air Temperature Observed (red dots) and modern equivalent (black line) air temperatures. The lower graph shows the range in expected sea-ice coverage - max andmin values from HadISST for 1961-90.
PressureThe seasonal cycle in pressure is much smaller than the short-term variability, so it's not very useful to compare modern averages with point observations. But, just to be consistent, here's the same plot for pressure: Observed (red dots) and modern average (black line) air pressures.
Sea-IceThe meteorological logs contain no explicit information on the sea-ice cover, but it is possible to make inferences about the state of the sea-ice from the information available. Sea-ice slows the ship down, it is associated with low sea and air temperatures, and complete sea-ice cover increases the air temperature variability (see AT graph above) - effectively switching from a marine to a continental climate. From each of these sources we can make an estimate of the sea ice cover: as proxy observations they are likely to be imprecise, but collectively they give a reasonable indication of the likely state of the ice coverage. Estimates of local sea-ice coverage from four different proxies (coloured points) and the range in expected recent sea-ice coverage - max and min values from HadISST for 1961-90. Despite the limitations of the estimates, it is clear that both winters (1821-2 and 1822-3) were harsher than those seen in 1961-90, with the period of complete ice coverage starting earlier and finishing later than even the maximum ice cover seen in 1961-90. During the trip out in 1821, sea-ice coverage was substantially greater than the 1961-90 minimum, and mostly comparable with or greater than the 1961-90 maximum - the exception being August and early September, when the 1821 coverage was somewhat less than the 1961-90 maximum.
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