| |
Main Hall
|
       |
|
You are El Nino Administrator. |
| Keynote #3 -- Dr. James O'Brien |
|
Item 6 23-MAR-1998 12:51 Phyllis Grifman (pgrifman)
Good day, and welcome to Week 3 of our Workshop. We've now reached the halfway mark (unless we all agree to continue later). I'd like to encourage everyone to participate, and to ask questions in our breakout rooms.
This morning, I have the honor of introducing Dr. James O'Brien as our third keynote speaker. Dr. O'Brien is the Director for the Center of Ocean-Atmospheric Prediction Studies at Florida State University, where he oversees a world-reknown program that utilizes ocean modelling to predict El Nino and other events and to perform research in air-sea interaction, ocean and coupled air-sea modelling, and climate prediction from month to decadal scales. In addition, the Center (COAPS) does statistical studies and prediction of the social and economic consequences of ocean-atmospheric variations.
Dr. O'Brien has had a distinguished career in science. He received his Ph.D. in Meteorology from Texas A&M University in 1966, and has taught, performed research, and served on numerous boards and honorary societies. Among his many citations, he has been honored as a Fellow by the American Association for the Advancement of Science, the American Geophysical Union, the American Meteorological Society, and the Royal Meteorological Society, by the the Oceanographical Society of Japan. He has received numerous governmental and univeristy awards, both in the United States and internationally, including the Medal of Honor from Leige University, Belgium, the Secretary of the Navy Professorship in Oceanography, the Office of Naval Research Distinguished Ocean Educator, as a Foreign Fellow from the Russian Academy of Natural Science. I could continue, but you can see his CV at http://www.coaps.fsu.edu/bios/obrien.html for a listing of honors, research positions, academic appointments, professional and university service, and publications.
Having had the pleasure of listening to Dr. O'Brien speak, I can assure you that in spite of this list of awards and honors, he is funny, approachable, and has made, through his speaking engagements and the COAPS web site, the complicated study of El Nino accessible to many, many people. He has made a web page for our workshop available at the COAPS site: http://www.coaps.fsu.edu/lib/enso-workshop.html
Please join me in welcoming Dr. O'Brien to the workshop. I look forward to an interesting and stimulating week of discussion.
Welcome, Dr. O'Brien,
Thanks for taking part in our workshop.
A comment and a question: I think it was important that you pointed out how the definition of "ENSO year" can make a big difference in what the statistics show us.
I wondered if the first chart "US Hurricanes" also included hurricanes that hit the West coast or is it just the Atlantic hurricanes? Thanks.
The first figure applies to Atlantic hurricanes making landfall in the U.S. The third figure applies to Pacific hurricanes and tropical storms making landfall in North or Central America. El Nino decreases the number of hurricanes making landfall on the Atlantic coast; whereas El Nino increases the number of tropical storms making landfall on the West coast. In this case, the impact on the West coast is opposite the impact on the East coast. The cold phase (also called La Nina) has the opposite effect on landfalling storms: less on the West coast, and more on the East coast.
El Nino is quite beneficial to the East Coast. There are less landfalling hurricanes, less tornadoes in most places, and the increased rainfall results in less forest fires in the following year.
Jim,
I keep hearing also about "El Viejo." Is this another name for La Nina or another side of the coin entirely (a three sided coin?)?
Have the data now started to show the warm pool off South America subsiding? Does this mean that the ENSO event is ending? Does that mean that as the current effect subsides, La Nina begins, or is there
a time lag effect?
Dr. O'Brien,
I teach all ages and find the elementary kids often ask many questions such as:
1. El Nino normally lasts at least 6 monthes...can it continue for a longer period, like a full 12 monthes or longer? Why??
2. The ocean has warmer surface temperatures during the El Nino phase, cooler surface temperatures during the La Nino phase, average surface temperatures during the neutral phase, is this correct?
3. Does the neutral phase have a Spanish name like El Nino or La Nina does?
4. In El Nino there seems to be a three month delay or time from the noting of the peak ocean water anomolies till the rain and storms develop over the land or continents. For instance SST peaked in December'97 and the severe, heavy, record breaking rains hit Sonoma County California in February. We had rain for 24 out of 28 days, flooded roads, mud slides, and flooding along rivers. Will there be a similar delay in the lack of rain or drought following the peaks of La Nina?
Thanks for your help!
Phyllis,
'El Viejo' is another name for 'La Nina'. It refers to the 'cold phase' of ENSO. The sides of the proverbial three sided coin are El Nino (the warm phase), El Viejo (the cold phase), and neutral conditions (times that aren't considered El Nino or El Viejo).
The water temperature off of South America tends to warm every year around Christmas time - it warms much more during El Ninos. These temperatures usually decrease during (the Northern hemisphere's) spring season. The warm water off of South America is still there. The indication of change comes from recent satellite observations of the sea-level height. The heights off of South America and in the Central and Western Pacific are changing towards the neutral conditions. This suggests that the winds are returning to the neutral conditions, and that the sea surface temperature should follow. However, it is not certain that this El Nino is ending.
El Nino events are not necessarily followed by El Viejo events. In some cases, there is no El Viejo event between El Nino events. There can be a one or more years of neutral conditions between the extreme events. In the last 100 year about 30% or El Ninos are followed imediately by El Viejo events.
Cathleen,
El Ninos conditions can last for more than a year. There are several cases of El Nino lasting two years (even three years by some less conservative definitions of El Nino years). We are not certain why they end, so it is "difficult" to say why some can last for more than one year.
The average sea surface temperature increases during El Nino years, and the average is colder during El Viejo years. However, there are locations that cool during El Nino years and others that warm during El Viejo years. When people refer to 'warming' or 'cooling' they usually mean specific regions of the Equatorial Pacific Ocean. The changes during El Nino years are not "equal and opposite" changes during El Viejo. Therefore, the neutral condition is not really the average of the warm and cold phases.
I'm not familiar with a Spanish name for the neutral phase. Feel free to let us know about any good suggestions.
There is a delay between the onset of an extreme phase and the effects on North America. The length of the delay depends on both the strength of the event and the location within North America. The precipitation is highly dependent on the position and structure of the jet stream, which is changed by El Nino and El Viejo events. For example, in neutral years precipitation tends to occur in the Pacific Northwest; but in warm years, it can occur in California or Mexico. The length of the delay in California would seem to be longer if the enhanced precipitation begins in northern Mexico rather than California.
I am trying to write an article updating the current status of the 97-8 ENSO event, and have gotten conflicting answers as to whether it's over. My understanding is the SST anomoly has narrowed and is arrayed on both sides of the equator, but is still quite large. Here in Southern California we have just gotten socked again with rain, but nothing like February, which set records.
1) what is current status, and has there been time to compare this event with 82-83 and others?
2) are effects in other parts of the world still being observed?
3) is the new data giving more credence to current computer model systems or discrediting them?
4) how have climate predictions made last summer stacked up against the actual conditions of the winter to date?
Dr. O'Brien,
I have just returned from looking at some of the "El Nino" effects to coastal California and have a few basis questions that I probably should have asked Monday.
1) Your statistical examination of El Nino and US hurricane landfalls is very interesting and convincing that there seems to be a connection. What are the likely physical linkages which could cause these statistical results?
2) What is the meteorlogical significance of a US landfall for a hurricane? I realize that to anyone living in its path, landfall is very important, but why did you choice to study only landfalls rather than all hurricanes?
3) Are there the same number of hurricane-creating storms for El Nino year, neutral years and El Viego years, but they do not have the right atmospheric conditions to work into full blown hurricanes? Where do the modifications in hurricane frequency originate?
Terry,
There are several factors to be considered in determining the 'status' of an El Nino event. Three of the most common are the sea surface temperature, the sea level heights, and the output of predictive models. The sea level heights and the models indicate that the event is winding down. If we go with the odds (2 indications out of three) the changes in water temperatures will presumably follow.
We are still seeing ENSO related changes in 'climate' throughout the western hemisphere. Here in Florida we have been getting drenched.
It's too early to tell how the models will do. They did a poor job of predicting the onset of El Nino; however, the advances in satellite coverage allowed us to see El Nino start even if it wasn't occurring in the computer models. Most of the models agree about the current decline of the El Nino, but we should wait and see if it really happens.
The climate predictions made last summer have held up quite well. We are still a few months from final numbers; however, many predictions came through, including heavy California and Florida rainfalls, and a milder winter in the north, heating needs were at a minimum, which in turn has brought us a drop in gasoline prices. El Nino inhibited last year's hurricane season as well, and depending on its decay time El Nino might effect this season as well. Some spring and summer effects due to El Nino are yet to be seen, including reduced tornadic activity in the southern plains.
Lesley,
1) The reduction in U.S. landfalling hurricanes during el Nino is principally the result of unfavorable upper tropospheric winds. The warm phase intensifies the subtropical westerlies over the Gulf of Mexico, Caribbean, and tropical Atlantic Ocean. Strong westerlies aloft are bad for hurricane formation. (If you hear the Weather Channel talking about wind shear, this is the problem I am discussing). Strong westerlies blow the tops off tropical thunderstorms and make it difficult for tropical cyclones to get organized. Worth noting, during el viejo, the subtropical westerlies are weaker making conditions more conducive for tropical storms and hurricanes.
2) Actually we have looked at all hurricanes and the impact of El Nino is the same as for U.S. landfalling storms: a reduction in hurricane numbers. As for why we focused on U.S. landfalls, you basically answered your own question. In terms of insurance, dollar damage, safety of the public, and hurricane preparedness, landfalling hurricanes are obviously of most interest to the public in general. Storms that do not hit the coast are a nuisance to shipping, but in the modern day rarely cause serious damage or loss of life. You are correct that in this study we neglect the storms that make landfall in Mexico or the Caribbean islands. Clearly these are of interest to these countries for the same reasons we are concerned with U.S. landfalling storms.
3) By "hurricane-creating storms" I am assuming you mean the tropical disturbances that come off Africa during hurricane season. A preprint from the most recent Hurricane Conference (S. Goldenberg and L. Shapiro) notes that the number of easterly waves (hurricanes form from these tropical disturbances) entering the Atlantic from Africa does not show much interannual variability. It is the atmospheric conditions over the Atlantic during a warm phase that reduces hurricane numbers.
The modifications in hurricane frequency principally originate in the Atlantic Ocean. It is there that the conditions are not favorable to support development.
It was interesting to partake in this form of information exchange. I thank the participants for their thoughtful questions. Additional questions that appear at this site in the next few weeks will also be answered.
Dr. O 'Brien,
Thanks very much for sharing information and ideas with us. We appreciate the time you spent here in the online workshop.
|
