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Blue Hill
Observatory 
Sky-mail
October 2009
Issue 9
IN THIS ISSUE
Storm Chaser Reed Timmer at the SNE Weather Conference!
Decreasing wind speed at Blue Hill?
Notes from the Observer's Office
The Observatory Store
Future Events
About The Blue Hill Observatory and Science Center
SNE Weather Conference - Saturday, October 24th
Discovery Channel's Storm Chaser Reed Timmer will be the after-dinner speaker!

This year's Southern New England Weather Conference will be on Saturday, October 24th at the Clay Center in Brookline, MA. Along with a full-day agenda featuring presentations from weather experts and professionals, there is also a dinner option and a post-dinner presentation from Reed Timmer, featured on Discovery Channel's Storm Chaser series.

Details about registration for the conference and the 2009 agenda are available on the weather conference website:  http://www.sneweatherconf.org/index.shtml  
Decreasing wind speed at Blue Hill?
Why is the Wind Speed Decreasing?
by Michael J. Iacono, Weather Observer, Blue Hill Observatory

The annual mean wind speed as measured at the Blue Hill Observatory has dropped by more than ten percent over the last thirty years. After remaining in a range of 15-16 mph for much of the last century, the annual average wind speed began a slow decline in the mid-20th century that has steepened significantly since 1980 to a record low value for any year of 12.6 mph in 2008.  The accompanying figure shows the trend in the annual mean (in black) along with running averages over 10 years (in blue) and 30 years (in red). 

Annual Mean Temperature plot

Wind speed is measured at Blue Hill with an instrument called a contacting anemometer that dates to the early 1960s. This three-cup instrument is mounted at the top of the highest wind mast on the Observatory roof about 50 feet above ground level, and this height has remained unchanged since 1908. The wind instruments were about ten feet lower prior to 1908.  The contacting anemometer is calibrated so that a nearly constant 640 spins of the instrument equal one mile of wind passing the Observatory.  Each time that count is reached, an electrical contact sends a signal to the indoor recorder, which makes a mark on a moving chart.  The marks are counted for each hour to derive the average hourly speed, that is, the number of miles per hour. To this day, low wind speeds are corrected upward slightly to ensure consistency of the present wind measurements with the similar preceding instrument.  The contacting anemometer is maintained and lubricated meticulously. It remains in excellent condition, and the bearings have insufficient wear to explain a drop in measured wind speed of the observed magnitude. 
 
Then why is the wind speed decreasing?  Several processes on local, regional and global scales are likely contributing.  Locally, on the summit of Great Blue Hill vegetation has grown nearly continuously during the 20th century after many years of intentional clearing during the 19th century.  The growth of trees may be slowing the wind as it passes over the hill, but this gradual growth is inconsistent with the sudden downward turn in the wind speed about 30 years ago.  In addition, substantial clearing of vegetation and some trees on the summit to the west (the prevailing wind direction) of the Observatory during the last decade has not affected the drop in wind speed.
 
Similarly, regional reforestation that has occurred over much of New England and the northern United States in the last 50 or more years may be contributing to slower surface wind speeds.  Other locations throughout the country, in particular the East Coast and Mid-west, have also seen lower wind speeds in recent decades.  
 
On larger scales, several research studies have shown using both climate model simulations and surface observations that the position of the main storm tracks that cross North America, which are generally associated with the jet stream, have moved northward. This may be impacting the frequency of storms and wind speed at the latitude of Blue Hill.  Wind is partly a result of a contrast in temperature such as across a strong cold front or between low and high latitudes.   The observed greater warming over the Arctic relative to middle latitudes is reducing this temperature contrast, which may also be a factor in lowering the wind speed.  Given the relevance of wind as a possible indicator of global climate change and its importance to efficient wind power generation, the Blue Hill Observatory will continue to monitor the wind carefully and consistently to help unravel the causes of the ongoing decline in wind speed. 
Notes from the Observer's Office
Three Inch Snowfall on Blue Hill on October 18th  
A cold rain turned to wet snow on Sunday, October 18th, which amounted to 3.0 inches before ending in the evening. This ties for the third highest snowfall in October with three other dates. Greater snowfalls in October include 6.8 inches on 10/10/1979 and 4.2 inches on 10/13/1934. The last snowfall in October brought 1.5 inches on 10/29/2005.
 From the Observatory Store
blue hill logoNew Merchandise Arriving Every Day!
We have a lot of great new merchandise arriving every day in the Observatory store, including a wide range of science kits, a collection of geology lessons and materials (including several rocks and minerals kits), books, and fun toys including Whirl-o Hurricanes.  We also have a fresh supply of snacks and beverages for hungry hikers, including TerraPass certified Climate Change Chocolate from Bloomsberry & Co.

The Observatory gift shop is open from 10:00 AM until 4:00 PM on weekends and many holidays.  You can arrange to visit the gift shop by appointment 7 days a week. For more information, to get a product list, place an order, or schedule a visit to the gift shop, please contact Don McCasland by phone: (617) 696-0562 or email: dmccasland@bluehill.org.
Future Events
Saturday October 24, 2009
Event: Southern New England Weather Conference
Location:  The Clay Center at Dexter and Southfield Schools, Brookline, MA
Hours: Full day event
Details: Visit the weather conference website for agenda and dinner option with Reed Timmer from Discovery Channel's Storm Chaser series!
 
Saturday October 24, 2009
Event: Dedham Climate Day
Location: Dedham Middle School
Hours: 11AM - 3PM
Details:  
http://www.dedhamclimateday.org
 
Sunday November 1, 2009
Event:
Kite making workshop at Wakefield Estate in Milton, MA
Hours: 1PM to 3PM
Details:  http://www.wakefieldtrust.org/

 
Saturday December 5, 2009

Event: Skywarn Awareness day
Hours: 9AM to 3PM

The gift shop, educational programs, and tours of the Observatory are available by appointment almost every day of the year. Please call ahead (617-696-0562) if there are questionable weather conditions.
About The Blue Hill Observatory
Blue Hill Meteorological Observatory, located at the top of a scenic mountain range south of Boston, is a unique American institution. Founded in 1885 by Abbott Lawrence Rotch as a private scientific center for the study and measurement of the atmosphere, it was the site of many pioneering weather experiments and discoveries. The earliest kite soundings of the atmosphere in North America in the 1890s and the development of the radiosonde in the 1930s occurred at this historic site.

Today, the Observatory is a National Historic Landmark and remains committed to continuing its extensive, uninterrupted climate record with traditional methods and instruments. The recently established Science Center expands this mission by enhancing public understanding of atmospheric science.

We are grateful for the generous support of members, friends, and corporations who make it possible to continue our benchmark climate observations and educational outreach programs.  Please contact Charles Orloff by phone: (508) 776-1879 or email: corloff@bluehill.org if you would like to make a donation to the Observatory.
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blue hill logo     Charles Orloff, Executive Director
     corloff@bluehill.org
     (508) 776-1879

     Don McCasland, Program Director

     dmccasland@bluehill.org
     (617) 696-0562
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