London Fog

We have just come through a three-day episode of fog, providing a timely subject for Words on the Weather, notwithstanding the current Arctic blast.

What is fog? It is a stratus or layer cloud that lies on the ground, thus the term ground fog. It is the 1 percent exception to the statement that 99 percent of all clouds result from the rising-expanding-cooling-humidifying process. The cooling that results in fog comes from contact between moist low-level air and the cold earth in a setting in which the air is still, limiting mixing between the low-level air and the drier upper-level air.

I had to drive to Salem (Oregon)Thursday. I chose to leave at midday rather than earlier because of the driving hazard caused by the thick fog. Even at noon-time, the fog was rather dense in pockets. But car headlights gave notice of approaching objects.

The fog would not qualify as a "pea-souper", but it caused me to return in memory to 1962, when I was involved in London's last "pea-souper"fog. This city had been notorious for its fogs, and why not? It had been common to heat dwellings by burning soft coal, sending soot up the multiple chimney stacks one still sees protruding from the roofs. The emitted smoke particles made ideal condensation nuclei in more than ample numbers -- a perfect recipe for fog to form when the air was still and the ground was cold.

I was at Imperial College in London 1962-63 to study cloud physics on a National Science Foundation Faculty Fellowship. We were living Barnes, a southwest suburb of London.

Imperial College was in Kensington. I got to work by taking one of London's famous red buses to Hammersmith and then riding the underground to the Kensington station.

As I recall, it was mid-December and getting colder. Air movement was stagnant. It was increasingly hazy.

One day I became aware that it was actually getting foggy inside my office. I decided it was time to get home ASAP. I got to the train station about 2:30 and wedged myself into a car. One more sardine packed into a tin. By the time we got to Hammersmith, it was getting dark and the fog was thick -- really thick!

Bus service had been discontinued, so I was faced with a mile-long hike to my house. I wrapped my muffler around my mouth and nose, as was the habit of the locals to strain out the dirty air, and set out to cross the Thames Bridge.

I walked for 15 minutes. Strange. No bridge. I stopped a muffled figure who loomed in my path. I asked "Where is the bridge?" He said "Sorry, mate. You are headed for the airport."

I backtracked to the train station and started off again, this time finding and crossing the bridge. At one point I found myself skirting the edge of Barnes Pond, now ice-covered. I could easily have walked into it. What then? Finally I arrived at my house, exhausted and thankful.

The fog lasted three more days. I didn't move from the house. Then colder air arrived from Siberia, as cold air has arrived from Alaska, and cleared out the fog. Super-cooled fog droplets impacted every twig, every blade of grass, leaving a winter wonderland of rime. It was gorgeous. I captured the beautiful scenes, but that was 35 years ago and I would be hard put to find the slides.

An addendum to the story:

London no longer experiences Sherlock Homes "pea-souper"fogs today. This is because of imposition of strict rules requiring the use of hard coal and electric fireplace starters.