The day before Statsraad Lehmkuhl docked in Norfolk, the crew experienced something unusual.
As Statsraad Lehmkuhl sailed north along the east coast of the United States toward Norfolk, smoke began to rise around the ship. The sea looked as if it were on fire, and on the horizon a strange vertical white line appeared.
Strong winds can make the sea foam, but this time only a breeze was blowing. Captain Jens Joachim Hiorth had an explanation for the smoke.
– The phenomenon is caused by cold air flowing over warm water from the Gulf Stream, creating sea smoke. When icy cold air passes over much warmer water, the ocean releases heat and moisture. The air cannot hold all the water vapor, which then condenses just above the sea surface. The result looks like smoke rising from the ocean, Hiorth wrote on the expedition’s Facebook page.
Warm sea, cold air
Statsraad Lehmkuhl was sailing in the Gulf Stream when the sea began to steam. The image to the left, below, show how this warm ocean current winds its way from the Gulf of Mexico, where it originates, and north-eastward along the US coast. The image to the right show the air temperature and wind direction.
The sea temperature was 23°C, which is 5°C warmer than normal, while a strong outbreak of cold air from the north - shown in blue - lowered the air temperature to just 10°C.
A waterspout
But what about the white line? It was a waterspout - the gentler cousin of tornadoes. Like the smoking sea, the waterspout formed because of the temperature difference between the seawater and the air above.
The sea warms the air close to the surface, and since warm air is lighter than cold air, a pocket of air begins to rise through the colder air above. Winds higher up cause it to rotate and form a vortex. The white color is not because the waterspout is sucking up seawater. It appears white because the air pressure inside the vortex is so low that the air cannot retain the water vapor, which condenses into tiny droplets.
The white column is therefore a cloud of tiny freshwater droplets; only right at the sea surface is seawater whipped up.
Storm force
Although waterspouts are not as dangerous as tornadoes, Captain Hiorth was wise to keep the ship well clear. They can easily damage the rigging. Wind speeds inside a waterspout can reach 30 meters per second; storm force.
Waterspouts are common along the southeastern coast of the United States in summer, but in winter they are rare, and a clear sign of just how cold the air was that flowed southward and out over the unusual warm ocean.
