Comparing historical and modern methods of sea surface temperature measurement – Part 2: Field comparison in the central tropical Pacific

Abstract

Abstract. Discrepancies between historical sea surface temperature (SST) datasets have been partly ascribed to use of different adjustments to account for variable measurement methods. Until recently, adjustments had only been applied to bucket temperatures from the late 19th and early 20th centuries, with the aim of correcting their supposed coolness relative to engine cooling water intake temperatures. In the UK Met Office Hadley Centre SST 3 dataset (HadSST3), adjustments have been applied over its full duration to observations from buckets, buoys and engine intakes. Here we investigate uncertainties in the accuracy of such adjustments by direct field comparison of historical and modern methods of shipboard SST measurement.We compare wood, canvas and rubber bucket temperatures to 3 m seawater intake temperature along a central tropical Pacific transect conducted in May and June 2008. We find no average difference between the temperatures obtained with the different bucket types in our short measurement period (∼ 1 min). Previous field, lab and model experiments have found sizeable temperature change of seawater samples in buckets of smaller volume under longer exposure times.We do, however, report the presence of strong near-surface temperature gradients day and night, indicating that intake and bucket measurements cannot be assumed equivalent in this region. We thus suggest bucket and buoy measurements be considered distinct from intake measurements due to differences in sampling depth. As such, we argue for exclusion of intake temperatures from historical SST datasets and suggest this would likely reduce the need for poorly field-tested bucket adjustments. We also call for improvement in the general quality of intake temperatures from Voluntary Observing Ships. Using a physical model we demonstrate that warming of intake seawater by hot engine room air is an unlikely cause of overly warm intake temperatures. We suggest that reliable correction for such warm errors is not possible since they are largely of unknown origin and can be offset by real nearsurface temperature gradients.

A Call for New Approaches to Quantifying Biases in Observations of Sea Surface Temperature

“…Physical models for biases in ERI SSTs have not been developed, as the detailed information required on individual installations (Matthews and Matthews 2013) is almost always unavailable (Fig. 2, right).…”

Isle of Man, Galapagos and sunspot data show net cooling hid double exponential ocean warming danger: +3°C in 2014, +4°C likely by 2016.

“…Taylor was a Newton-Hooke experimental scientist and, like the author, a keen sailor especially in coastal shelf seas. He would no doubt discover the truth of the ocean boundary layer from in situ experiment as we did [1] [2]. Like everyone else however, Taylor was not infallible.…”

Comparing historical and modern methods of Sea Surface Temperature measurement – Part 2: Field comparison in the Central Tropical Pacific

“…Original data were collected on a 5-week research cruise from Papeete, Tahiti to Honolulu, Hawaii aboard the SSV Robert C. Seamans of the US Sea Education Association from May 9th to June 14th 2008 (Siuda, 2008;Matthews, 2009). The Seamans is a ∼ 41 m-long modern sailing vessel of draft ∼ 4 m, achieving on our cruise an average speed of around 4.7 ± 1.8 kt (∼ 2.4 ± 0.9 ms −1 ) under-sail and 7.2 ± 1.7 kt (∼ 3.7± 0.9 m s −1 ) under-motor.…”