Boston Harbor & Islands Science Symposium Northeastern University, 11-12 April, 2017 THE COASTAL INFLUENCE ON LOCAL CLIMATE CHANGES AT THE BLUE HILL METEOROLOGICAL OBSERVATORY MICHAEL J. IACONO1,2, DON McCASLAND1, and JONATHAN O’BRIEN1 (1) Blue Hill Meteorological Observatory, Milton, MA, USA ([email protected]) (2) Atmospheric and Environmental Research, Lexington, MA, USA

Blue Hill Observatory Background Climate Changes at BHO Since 19th Century Coastal Influence on BHO Climate Changes

Sea-Breeze/Backdoor Front Climatology • Location: Summit of in Milton, Annual Temperature Description: (10 miles SSW of , 7 miles SW of Boston Harbor) • Wind direction shift • Founder: Abbott Lawrence Rotch on February 1, 1885 • 30-year mean now to east during day • Elevation: 635 feet (194 meters) above mean sea-level. warmer than 1870s by 4°F (2.2°C) • Wind speed jump • Climate: Longest continuous weather records in North America • Little or no rain (1885 to present). Observer on duty every day of the year. • Large decadal • Large temperature variations • Designation: National Historic Landmark (1989) decreases: • Global and local • Webpage: www.bluehill.org • 13°F in 5 minutes on influences May 11, 1996 • 29°F in 20 minutes on May 9, 2000 • 32°F in 1 hour on April 16, 2003 Annual Precipitation • 38°F in 2 hours on April 17, 2002

• 30-year mean rising since mid-20th century Winter Temperature Trends by Wind Direction • More rain expected in warmer climate • Largest increases • Large inter-annual from NW-E changes • Decreases or Weather Observations smallest increases from SE-SW • Quality: Traditional observing methods and instruments are Annual Wind Speed used to ensure long-term consistency • May indicate larger • Parameters: • 30-year mean falling influences from Outdoor Instrument Enclosure: Temperature sharply since 1970s land than ocean Dew Point Temperature and Precipitation • Due to vegetation Precipitation Snowfall growth or global Snow Depth circulation changes Wind Speed / Direction Annual Wind Speed Trends by Wind Direction Peak Wind Gust Station Pressure • Annual mean wind speed by Sunshine Duration wind direction for 1970-1982 Cloud Cover Annual Sunshine (blue) and 2000-2012 (red) Cloud Types • Percent wind speed decreases Visibility, etc. • Increase 1950s-60s from 1970-1982 to 2000-2012 are • Historic Instruments: may have been larger for overland directions (S, Hazen Shelter: cloud/ocean influence SW, W, NW and N), than onshore Thermometers • Decrease 1970s-80s directions (NE, E and SE).

due to air pollution • May indicate larger impact from • Increase since 1990s reforestation over continental US due to fewer aerosols or shifts in circulation rather than Ombroscope: Campbell-Stokes (less air pollution) intensity of ocean storms. Time of Precipitation Sunshine Recorder