Saturday, December 19, 2015

El Niño

The strongest El Niño since 1997-98 will likely emerge as 2016 unfolds. The 2015-16 El Niño is expected to impact the distribution, intensity, and frequency of precipitation, tropospheric ozone, and wildfires around the world.

NASA satellites have been monitoring the impact of El Niños over the past 15 years.

Deviation from mean surface water temperatures
17 December 2016
source: NOAA

El Niños occur when equatorial Pacific Ocean temperatures warm up over a prolonged period of time. NOAA defines this period as a 3-month increase in the mean surface water temperature of 0.9 °F (0.5 °C) or more in the east-central tropical Pacific.

Increased surface water temperatures feed heat and moisture transport into the atmosphere by intensifying convection. Convection occurs as heat from the ocean warms the air as it flows over the ocean surface. The warmer air expands, becomes less dense, and rises. This process creates a conduit of heat and moisture that fuels storms.

Contrasting higher than mean temperature deviations in an El Niño event, a La Niña event is characterized by a lower than mean temperature deviations.

Scientists analyze data to determine how it fits with reasonably well-understood physical models of some aspect of a weather system whether it's convective heat flow, fluid transport, gas transport, or other phenomena. Weather systems are notoriously complex. Weather has far-reaching, often unforeseen impacts.
"Big whirls have little whirls,
That feed on their velocity;
And little whirls have lesser whirls,
And so on to viscosity."
Lewis Fry Richardson

Storm swell attributed to 2002-03 El Niño
Ocean Beach, San Diego
source: PD