Dr David J. Webb
Dr David J. Webb
National Oceanography Centre, Southampton, U.K.
Position: Emeritus Fellow
Group: Global Climate
NOC Page:
https://noc.ac.uk/n/David+Webb
This project has involved analysing data from a high resolution global ocean model with the aim of obtaining a better understanding of the oceanic processes involved in the development of El Niños.
The main paper resulting from this study is Webb (2018a). There have also been two technical reports. These are Webb (2018b) and Webb (2016). A video of a seminar summarising the study is available on YouTube(★★★?).
The 2018 paper analysed model results for periods including the strong El Niños of 1982-1983 and 1997-1998. It showed that during the development of these El Niños, the transport of warm water in the Pacific was dominated by the North Equatorial Counter Current (NECC). The results also indicated a number of physical mechanisms responsible for the increased heat transport during the El Niño.
The first of the follow-up papers (Webb, Coward and Snaith, 2020) compares key aspects of the model with satellite radar altimeter and sea surface temperature measurements during the 1995-2000 period. This failed to find any significant error in the model results giving further confidence to the results and hypotheses put forward in the 2018 paper.
Webb (2021) investigates the cause of the drop of sea level in the North Equatorial Trough prior to strong El Niños. It finds that this is due to Ekman pumping resulting from the local winds. The study also finds that this is a necessary but not sufficient condition for the triggering of strong El Niños.
Webb (2025a) uses ERA5 data to investigate convection in the atmosphere during each September and compares the average pattern with that occurring during the development of the strong El Niño of 1982-83, 1997-98 and 2015-16. The results show that when strong El Niño are developing, there is much more deep atmospheric convection than normal along the line of the Inter-Tropical Convergence Zone in the central and eastern Pacific.
Overall these results indicate that the high temperature of the North Equatorial Counter Current, in the central and eastern Pacific, is at least partly responsible for the development of strong El Niños.
Webb (2025b) tests this hypothesis with the use of the CESM climate model. Following a control run, a series of forced runs are carried out in which the temperature along part of the North Equatorial Counter Current is increased by 1°C. A comparison is then made of the average of different fields during the following month. The results show that the temperature of the NECC affect all El Niños, not just the strongest. This occurs because the month to month and year to year fluctuations in the temperature of the NECC, lies in a range where convection in the tropical atmosphere is particularly sensitive to ocean temperature.
Before becoming involved in the El Niño study I wrote a series of papers on continental shelf resonances which affect the tides and result in the dissipation of large amounts of tidal energy.
The first of these papers was Webb (2012), on the Gulf of Carpentaria, followed by Webb (2013a) on the resonances of the English Channel and the Irish Sea and Webb (2014a) on the resonances of Hudson Bay and Hudson Strait.
The Hudson Bay and Hudson Strait region is of particular interest, first, because it absorbs almost half the energy of the semi-diurnal tide in the North Atlantic and, secondly, because it acts almost like a black hole, absorbing at some frequencies over 90% of the incident tidal energy.