Our planet’s rotation on its axis and atmospheric heating produce a steady flow of major jet streams that head from west to east; these streams break in and out of one another, merge, twist and flow between the troposphere and stratosphere. These jet streams are very heavily affected by changes in the Earth’s atmospheric and ocean conditions, and a number of cycles influence varied jet stream paths that deliver anomalous weather to several parts of the globe.
El Niño-Southern Oscillation (ENSO)
The phenomenon often called simply ENSO is an abnormal cooling or warming of the surface waters in the equatorial Pacific accompanied by an atmospheric pressure change fluctuation between the equator’s eastern and western Pacific waters. ENSO is the entirety of the climate cycle, both surface temperature anomalies and atmospheric conditions. Regardless of the direction in temperature fluctuation on the ocean’s surface, ENSO events can cause anomalous temperature and precipitation amounts across North America and either increase or decrease cyclone development in the eastern Pacific and Atlantic basins. Due to the United States easterly location in regards to ENSO, the jet stream’s normal course is altered, bringing unexpected weather to the States.
During El Niño events when the sea surface temperatures are above average, the jet stream diverges from its usual meandering path across the Pacific and through the US and instead forms a persistent jet stream that beelines through the Gulf of California into the Gulf of Mexico and past Florida, causing increased precipitation in California and in the Gulf Coast. A dipping polar jet stream with more strength than usual tends to wander southerly trapping warmth in the north states and bring increased rainfall to the southeast portions of the US. Other areas affected include the upper Midwest and Great Lakes, who see less than normal snowfall; places such as the Sierra Nevada Mountains and the southern portions of the Rocky Mountains will receive increased snowfall amounts. Beyond our climate, the jet stream situated in the heart of the tropics has its strength increased by the excess heat in the Pacific; this heat fuels the creation of cyclones in the eastern Pacific.
The cold-water sister to El Niño, La Niña influences both the pacific and polar jet streams into variability. This causes a severe dip in the polar jet stream, bringing cold air across Alaska and western Canada. The variable pacific jet stream tends to bring rain and cool temperatures to the Pacific Northwest and wet winters to the Midwest and Great Lakes. During these events, Europe sees a stronger Atlantic jet stream, translating to increased precipitation. Our recent winter here in California has been a great symbol of La Niña’s alterations on our season, bringing decreased rainfall and warm temperatures. Our current La Niña is expected to continue through spring 2012.
The NOAA’s networked bouy system TAO/TRITON feeds reams of data on current ENSO conditions, and these 3D visualizations by the NOAA show how our current La Niña is evolving.
- Upper Ocean Temperature and Dynamic Height
- 20°C Isotherm and Upper Ocean Temperature at the Equator
- 20°C Isotherm and Upper Ocean Temperature and Current at the Equator
- Sea Surface Temperature, Winds, 20°C Isotherm and Upper Ocean Temperature and Current at the Equator
- “ENSO Impacts on United States Winter Precipitation and Temperature”. The NOAA’s Climate Prediction Center. Retrieved on January 27, 2012.
- “El Niño (ENSO) Related Rainfall Patterns Over the Tropical Pacific”. The NOAA’s Climate Prediction Center. Retrieved on January 27, 2012.
- “El Niño/Southern Oscillation (ENSO) Diagnostic Discussion”. The NOAA’s Climate Prediction Center and the International Research Institute for Climate and Society. Retrieved on January 27, 2012.
- “La Niña Information”. NOAA. Retrieved on January 27, 2012.