The 1982-83 El Nino
California, Gulf Coast, Hurricane Season, and
Other Global Effects
Another excerpt from this report shows the widespread Global effects attributed to the influence of this strong El Nino (though remember, no one event can be directly attributed to El Nino, but El Nino can be the cause of the conditions coming together for these events to occur):
"... the economic impacts of the 1982-83 El Nino were large. Along the South American coast, the losses overshadowed the windfalls. The fishing industries in Ecuador and Peru suffered heavily when their anchovy harvest failed and their sardines unexpectedly moved south into Chilean waters. Farther to the west, abnormal wind patterns steered typhoons off their usual tracks to islands such as Hawaii and Tahiti, which are unaccustomed to such severe weather. They also caused the monsoon rains to fall over the central Pacific instead of on the western side, which led to droughts and disastrous forest fires in Indonesia and Australia. Winter storms battered southern California and caused widespread flooding across the southern United States, while northern ski resort owners complained of unusually mild weather and a lack of snow. Overall, the loss to the world economy in 1982-83 as a result of the climate changes amounted to over $8 billion. The toll in terms of human suffering is much more difficult to estimate."
The strong 1982-83 El Nino warmed the waters of the equatorial Eastern and Central Pacific by 3.5+ degrees Celsius. Scientists declare an El Nino event if the sea surface temperatures (SSTs) exceed 0.5 degrees Celsius on average for three months straight. This is an indicator of how strong this event was compared to other El Nino events.
Normal Year Conditions - The Walker
Circulation, Trade Winds, and Thermocline
The Walker Circulation is the basic setup of the equatorial Pacific Ocean. The Trade Winds blow west, dragging across the surface waters, which causes the water to collect at the western end of the Pacific Basin. This creates a greater volume of warm water in the west and thus lower water pressure. The cooler water deeper down then flows toward the eastern end of the Pacific Basin, where its volume collects, and since cooler water is more dense, the water pressure is higher here. The Thermocline becomes tilted with a shallow layer of warm water to the east and a deeper layer of warm water to the west. Since cooler water is near the surface in the eastern Pacific, subsidence inhibits convection, and atmospheric conditions remain clear and dry (higher barometric pressure). The warmer waters in the western Pacific promote convection with rising air currents, thus giving us cloudy and wet conditions (lower barometric pressure). This is the normal Walker Circulation scenario.
As the Trade Winds blow across the water, the water just under the surface is moved at a 45º angle due to the effects of the Earth's spin (this momentum of the Earth is called the Coriolis Force). In turn, the deeper waters are moved another 45º causing them to move at a 90º angle to the direction of the wind. This displacement of surface waters causes upwelling from the depths, which is normally cooler water being brought to the surface. Due to the tilt of the Thermocline, the upwelling waters in the East Pacific are cooler than the waters upwelling in the West Pacific, which aids in keeping the Walker Circulation persistent.
When the Trade Winds weaken due to a burst of westerly winds from a thunderstorm system moving east near the equator, or from a Kelvin wave moving the warmer waters east and changing the tilt of the Thermocline, then the Walker Circulation reverses, bringing clear and dry conditions to the Western Pacific and cloudy and wet conditions to the Central and Eastern Pacific. If the sea surface temperatures remain on average 0.5 degrees Celsius above normal for three months, the onset of an El Nino is declared. Normally cool waters get warmer (affecting the Humboldt Current) and normally warm waters cool down, normally wet conditions turn dry and normally dry conditions turn stormy, and the winds don't carry the air as they usually do.
The 1982-83 El Nino as Compared to Normal
The anomaly of El Nino years compared to normal years shows a fairly consistent reverse of Walker Circulation conditions in the left chart below. (Amomalies indicate abnormal conditions compared to normal conditions.) In addition, sea level pressure (barometric) anomalies are illustrated in the right chart. This shows the higher pressures in the Western Pacific over cooler than average waters, and the lower pressures in the East/Central Pacific over warmer than average waters. Notice the large purple area over the U.S. Northwest. This is showing the wetter than average weather that brought so much rain to California. Also, the blue over the Gulf Coast area indicates more than average rainfall. Low pressure areas are conducive to convection and storm formation. The calculation for the sea level pressure anomaly is called the SOI (Southern Oscillation Rate), and is based on the difference between departures from average barometric pressures at Tahiti and Darwin, Australia. Positive departures indicate El Nino conditions, and negative departures depict La Nina conditions (again, the opposite of El Nino, though not as bold).
Jet Stream and Storm
As the Jet Stream shifts eastward, the left-exit region of the Jet Streak (where upper level divergence initiates a frontal low to form, bringing rainy/stormy conditions) moves closer to the West Coast of the United States (see chart below). This is what brings wetter than average weather to California, including more than average snow in the mountains, thus making this event an effect influenced by El Nino conditions. Not caused, but influenced. And to what do we attribute this shift in the Jet Stream and how is it connected to El Nino? The warming conditions brought on by El Nino cause a large north-to-south temperature gradient in the upper levels of the atmosphere, which produced a bipolar field of height anomalies, allowing the Jet Stream to surge eastward. Also note the storm track over the southern U.S. and into the Atlantic, which is the probably cause of the weakened Tropical Cyclone season for 1982 and 1983 (compared to normal years 1980 and 1981).
Even though you cannot blame El Nino directly for any precipitation or temperature anomaly, the set of charts below show that El Nino is fairly consistent in affecting these conditions whenever it is present. Some El Nino years are stronger and longer than others, as evidenced here, but the indirect affects still occur frequently. I have circled the 1982-83 El Nino map for easier comparison. 1982-83 was a pretty strong El Nino year.
Temperatures and Sea Level Pressure
The Hurricane Seasons of 1982 and 1983
In the 1982 tropical season, there were only five (5) named storms. Two (2) made hurricane status, and only one (1) reached major hurricane strength (a Category 4 with my name, Debby (though spelled differently), no less!). The timing of the storms was within normal parameters (June 2 - October 2), but only one made landfall (Tropical Storm Chris on September 11, 1982 at Port Arthur, TX/Lake Charles, LA). The rest spent their entire time over water, including the Category 4 Debby. Hurricane Alberto (Cat 1) formed June 2 over the Yucatan/Gulf of Mexico, Tropical Storm Beryl formed August 28 from Cape Verde, Hurricane Debby (Cat 4) formed September 13 from Cape Verde, and Tropical Storm Ernesto formed September 30 in the North Atlantic. There was one interesting note, though. A subtropical storm formed June 18 in the Gulf of Mexico, made landfall in Brevard County, northern Florida, moved out into the Atlantic, and became an extratropical storm south of Newfoundland. The Preliminary Report signed by JMP 7/15/82 on the website reads as follows:
"A subtropical depression developed rapidly over the eastern Gulf of Mexico on June 18. It resulted from interaction of a tropical disturbance moving northward from the Yucatan Peninsula and an upper level trough in the westerlies advancing from Texas. Although such an occurrence is unusual, a remarkably similar storm formed in the same area during June 1974."
The 1983 tropical system saw only four (4) named storms, three (3) made hurricane status, and none (0) reached major hurricane strength. Two (2) of the three (3) hurricanes made landfall, as did Tropical Storm Dean. Hurricane Alicia formed in the Gulf of Mexico on August 15 and made landfall on August 18 25 miles south of Galveston, TX as a minimal Category 3 storm. Hurricane Barry (Cat 1) formed from Cape Verde on August 23 and made landfall on August 28 as a Tropical Depression in central Florida. Hurricane Chantal formed near Bermuda on September 10 and did not make landfall. And Tropical Storm Dean formed on September 22 from subtropical origins in the Atlantic (from a frontal cloud band off the East Coast that became stationary from the Bahamas northeastward beyond Bermuda), developed tropical characteristics on September 26, and made landfall on September 30 in Virginia. Hurricane Alicia is worth noting again because it was "the first storm where landfall probabilities were issued by the National Weather Service." Also from the Preliminary Report (not signed) on the website:
"Hurricane Alicia was the first hurricane to strike the continental United States since Hurricane Allen moved over extreme south Texas on 10 August 1980. The three years and 8 days between these strikes is the longest period in this century that the United States mainland has gone without a hurricane landfall. The next longest period was from 28 September 1929 to 14 August 1932."
As noted in the section on global effects above, the lowered activity of tropical systems in the Gulf of Mexico and Atlantic Ocean can be indirectly attributed to El Nino since the Jet Stream shifted its storm track to a more southerly location across the U.S. These fast, upper-level winds have the capability to inhibit development and westward movement of tropical systems due to wind shear and upper-level steering winds. However, more analysis needs to be done to determine how much El Nino is responsible for this weak Hurricane season.
This has encouraged a future project, an addition to this e-portfolio. Using the resources cited for the charts above, I can go back and select the Atlantic Ocean to compare the SSTs, OLR, SLP, Precipitation Rate, and Jet Stream location to see what part of El Nino might have indirectly had this effect on the 1982-83 Tropical Seasons. Of course, the climatology of the Atlantic hurricane basin has historically shifted phases of activity periodically, which has nothing to do with El Nino or La Nina. But I think it would be worth investigating to determine how far-reaching the effects of El Nino can be. Also, it would help to determine if El Nino events would be a precursor to weakened or heightened tropical cyclone activity (depending on what part of the globe, Atlantic or Pacific).
As for reflections on this project, I found it fascinating to see the anomalies and chain-reactions of conditions that were caused by something so subtle as a few degrees difference in sea surface temperature. Also, the interactions of so many and diverse weather and climate occurrences is a fascinating play in harmony and cause-and-effect. When thinking of an El Nino event, one thinks of dominos. I've heard talk of El Nino but never understood its nuances and implications. I found this project very enlightening in all the different factors that go into the making of an El Nino scenario.
Meteo 241 e-Portfolio Project #3
November 5, 2005