Pacific Decadal Oscillation - Another Player in the Climate Game

An anchorman on one of the major networks recently mentioned the "Pacific Decadal Ocsillation" during a story about weather. I'd heard about the PDO during my involvement in a research program at the Montana State University Paleoclimatology Lab a couple years ago, but never really understood it - and certainly didn't expect to be hearing about it on the 5 o'clock news!

In my quest to learn more, I found a few websites that provided explanations posted by various organizations. The State Climate Office of N. Carolina provides a general explanation that was very helpful, considering my limited expertise in this area. According to the climate office, The Pacific Decadal Oscillation (PDO) is a pattern of Pacific climate variability similar to ENSO (El Niño - Southern Oscillation) in character, but which varies over a much longer time scale. The PDO can remain in the same phase for 20 to 30 years, while ENSO cycles typically only last 6 to 18 months. The PDO, like ENSO, consists of a warm and cool phase which alters upper level atmospheric winds (compare PDO and ENSO). Shifts in the PDO phase can have significant implications for global climate, affecting Pacific and Atlantic hurricane activity, droughts and flooding around the Pacific basin, the productivity of marine ecosystems, and global land temperature patterns. Experts also believe the PDO can intensify or diminish the impacts of ENSO according to its phase. If both ENSO and the PDO are in the same phase, it is believed that El Niño/La Nina impacts may be magnified. Conversely, if ENSO and the PDO are out of phase, it has been proposed that they may offset one another, preventing "true" ENSO impacts from occurring.

According to the University of Washington's Joint Institute for the Study of the Atmosphere and Ocean (JISAO), during the warm phase (aka positive phase), higher than normal sea-surface heights caused by warm water form a horseshoe pattern that connects the north, west and southern Pacific, with cool water in the middle (map). During most of the 1980s and 1990s, the Pacific was locked in the PDO's warm phase (see graph below), during which these warm and cool regions are reversed. The JISAO site also notes that "Pacific Decadal Oscillation" was coined by fisheries scientist Steven Hare in the mid-1990's while researching connections between Alaska salmon production cycles and Pacific climate.

Like the ENSO, the cause of the PDO is not understood - and like the ENSO, we may be hearing (and learning) more about the PDO in the years to come. Finally, here is a 6-minute YouTube explanation of the POD.

Polar Vortex Grabs Media Attention!

Several years ago, in attempt to understand ozone depletion, I learned of the role that the (southern) polar vortex plays in the forming the "hole in the ozone" over Antarctica every September-November (spring in the southern hemisphere). The southern vortex contributes to the formation of the hole by isolating the air over Antarctica every winter-spring, and then breaks up every December (summer in the southern hemisphere), so the hole goes away. Although the vortex forms during the winter, the hole doesn't form until the spring because sunlight is needed separate Cl atoms from the CFC molecules - and there is no sunlight over the South Pole during the winter. To learn more about the role the southern vortex plays in ozone depletion, CLICK HERE (NASA site).

The NASA graphic above shows the correlation between ozone depletion, the location of the vortex, and temperature over the Arctic. The globe on the left shows that there is ozone depletion over the Arctic (every spring), but it is not bad enough to be called a "hole". To learn more about why ozone loss is worse over the South Pole, why the hole only forms in the spring (Sept-Oct), and the conditions that team up to cause the hole, CLICK HERE.

Although, the southern vortex is bigger, stronger, and lasts longer than its northern counterpart, it was the northern polar vortex grabbing all the headlines last week. There's NEVER been as much news coverage about the vortex as there was during the recent cold spell - In fact, very few Americans had ever heard of the polar vortex until this outbreak of cold weather. Here are some sources that may be helpful:

1. The Washington Post has a informative page about how the (northern) polar vortex caused those bitter cold temperatures. The page includes links and graphics.

2. Take a look at this NOAA site.

3. Here is a site that has great graphics from Climate Central.

To view a convenient list of all the resources that have been posted on this "Earth Science Guy" blog site, CLICK HERE.

Mr. Bouchard's Site for Earth Science Teachers

This week's resource is a site created by Mr. Bouchard, a teacher at Earl L. Vandermeulen High School in New York. The site includes dozens of PowerPoints 31 labs, and other resources. CLICK HERE to access the many resources Bouchard has to share.

If you know of any other sites designed specifically for Earth Science teachers, please let me know. Here is my "Rodney's Homepage for Earth Science Teachers": www.formontana.net/home.html. You will find my email address there.

Positions of the Continents Interactive

This week's resource is a neat interactive provided by EarthGuide, which is part of the Geosciences Research Division at Scripps Institution of Oceanography. CLICK HERE to try it out.

What the hail? - Animation Shows the Role of Updrafts

To help students understand how updrafts in a mature thunderstorm can cause hail to grow this large, show them THIS ANIMATION and then CLICK HERE for a detailed explanation.

Right: This hailstone is the largest ever verified in the USA: 8.0 inches in diameter, 18.5 inches in circumference, and 1.9375 pounds. It fell near Vivian, South Dakota in 2010. Lee Scott, who collected the stone, planned to make daiquiris out of the hailstone but decided to put in a freezer before taking it to the National Weather Service for certification (source: Weather Underground). CLICK HERE for more great hail trivia from Weather Underground, including an aerial photo of a town that received 18" of hail in one storm!

Also, CLICK HERE to see an impressive satellite view of the Hi-Line (north-central Montana) before and after a 2007 hail storm.

To view a convenient list of all the resources that have been posted on this "Earth Science Guy" blog site, CLICK HERE.

Below: Map courtesy of the Insurance Institute for Business and Home Safety - CLICK HERE to see a larger version of the map.

64-yard Field Goal in Denver's Thin Air

A fun way to introduce students to a study of the atmosphere is to discuss field goals and home runs.

In 2003 Helena High's Dan Carpenter kicked a school-record 53-yard field goal on a warm, sunny, Saturday in October. Arguably that kick earned Dan a scholarship - and today he is the kicker for the Buffalo Bills. To get things started, I tell students about Dan's kick and ask them why that day and that location (Helena) were favorable for kicking the long field goal (there was no wind). As it turns out, on a warm day at high altitude air molecules are more spread out, resulting in less friction on the ball (fewer collisions) as it travels through the air. Interestingly, the density of the air in Denver is only 82% that of air at sea level. To learn more about this go to this web page.

Greatest Kicks in the NFL
Eventually our discussion turns to the NFL, as we look at the longest field goals ever kicked. Until this past weekend, 3 kickers shared the record at 63 yards. Two of those were kicked in Denver, and one was kicked in New Orleans by Tom Dempsey in 1970. I actually show them a YouTube video of Dempsey's kick. Keep in mind that New Orleans is below sea level. This past Sunday, December 8, Matt Prater kicked a NFL record 64-yard field goal in Denver. It is a huge advantage to kick in Denver because of the elevation - but Prater did kick his field goal on a cold day.

What about baseball?
The same principles apply to the flight of a baseball, so Denver's Coors field is a favorite among home-run hitters. By some estimates a baseball will travel 30 feet farther in Denver (compared to sea level). Try this interactive home run simulator see how altitude affects the distance a baseball will travel.

So what about humidity?
Water molecules are less massive than the nitrogen and oxygen molecules they replace, so collisions with water molecules have less influence on the flight of the ball. However, in baseball the balls actually absorb moisture in humid conditions, which makes them a bit heavier - and more importantly it makes them a little softer (less bouncy). In fact baseballs used at Coors Field are actually stored in a humidor to soften them up and counter the affect high altitude. To learn more about the humidor and the situation at Coors Field (including a really good PowerPoint presentation), CLICK HERE. I've often wondered whether the humidity in New Orleans helped or hindered Dempsey's historic kick in 1970.

To view a convenient list of all the resources that have been posted on this "Earth Science Guy" blog site, CLICK HERE.

NWS Summary of November 17 Tornado Outbreak

The image shown here is a time-lapse of the tornado that ripped through Washington, IL on November 17, 2013. The colors show precipitation intensity (called a "reflectivity" image). The pattern of precipitation formed a distinct "hook" shape (larger version of image), indicating the thunderstorm had developed rotation (a mesocyclone) on its SW side. Rotation does not guarantee that a tornado will form, but it it a precursor - and this one did spawn a tornado. Evaluation of the aftermath indicated the intensity reached EF-4 as it moved through Washington, IL (aerial photos). Amazingly there were only 2 deaths in the city of over 15,000. Cell phone warnings alerted many who were in church. CLICK HERE to see/read other storm summary resources posted by the National Weather Service. This Wikipedia page is another good source. Also, check out this RADAR PowerPoint presentation that I have posted.