Stephanie Ball, ex-Met Office and now running her own weather consultancy business, explains how satellite data helps her to produce more accurate forecasts for Gibraltar.
05, November 2020
I began my career with the Met Office in 1986 as a research assistant in the Cloud Physics Research department. But it wasn’t until a move into the Central Forecasting Office in Bracknell, that I first came across the use of satellite imagery. In those days imagery arrived by a MUFAX Transmitter, but thankfully things have moved on a long way since then — not just in delivery, but with the introduction of new generation satellites, such as MSG.
I have to be honest and say that while satellite data always played a very important role in my forecasting process, it wasn't until my move to Gibraltar that I really came to appreciate the processes that satellite imagery could reveal for this area — especially in respect to the boundary layer.
Since my arrival in Gibraltar six years ago, I have been in awe of the local weather processes which take place here. If you want to watch physics and the process of fluids in motion then you couldn't choose a better area. Not least in the study of Gibraltar's Levanter, pictured above (Credit: MeteoGib)
Being a boat user, and very mindful of safety at sea, it is the use of MSG products, such as the cloud top pressure or temperature, which I have found invaluable in the detection of sea fog or where it may develop, when visible imagery is not available.
The Strait of Gibraltar acts as an exchange of water between the Atlantic and the Mediterranean with two currents existing, but it is the cooler current of Atlantic water (Atlantic Jet) which replenishes the water of the Mediterranean. This is the more important, especially in summer when it becomes more pronounced.
An anticyclonic gyre (Western Alboran Gyre) is generated which runs from the Strait of Gibraltar, along the Malaga coast and then dives south and returns west along the Moroccan coast.
In the summer, MSG cloud top temperature products help to distinguish the subtle changes in temperature in this boundary layer close to the water’s surface, and as evaporation increases the gyre becomes more pronounced and visible. This is where fog is more likely to form as warm air advects over the colder waters, so it helps to pinpoint the possible location of fog more accurately.
This is not the only source of colder waters though, there is also the process of coastal upwellings produced through the Ekman transport of water. One such, very important, upwelling is found off the Malaga coast in summer. It is produced when a strong, very warm and dry, offshore wind called the Terral develops and pushes surface waters away from the coast. This water is then replaced by an upwelling of colder water from below and can lead in a drop of water temperature here, by as much as 5 to 10 degrees.
This cold upwelling is responsible for a lot of the summer fogs which affect the Malaga coast, with these more local, colder patches of water again detectable by cloud top temperature products. These Malaga fogs not only plague the Costa del Sol, but at times when a morning sea breeze springs up, they can be carried west towards Gibraltar, example pictured below (Credit: MeteoGib).
The use of MSG products can be vital in detecting these cold waters, but that doesn’t always mean fog is present, as many other processes are involved. But until visible imagery becomes available during the morning, these products, and the frequency that they can be updated, are the only valuable tools for detecting fog banks, in this case sea fog. With the frequency of images available, it is possible to detect ekan advecting fog bank and to try to determine an estimate of its direction and speed.
While the detection of fog is important for the sailing community, it is also of equal importance to the aviation sector — in respect to flights arriving and departing from Gibraltar Airport, where fog could on occasion result in diversions to Malaga. Forecasting for the airport was an integral part of my job when I was Senior Operation Meteorologist at the Met Office.
Now that I am running my own business specialising in marine forecasting (MeteoGib), I equally make use of these MSG products, but nowadays my attention is more on the waters where I use social media to forewarn the local sailing community of possible fog hazards and hopefully help to aid safety.
Follow Stephanie on Twitter @MeteoGib