WEEK TWO: 12-16 September 2011

• Harvest Moon -- A full moon that occurred early Monday morning is known as "Harvest Moon" since it is the full moon nearest the autumnal equinox. The name Harvest Moon originates from a legend that arises the moonlight from the nearly full moon provides mid-latitude farmers with extra natural light for harvesting their crops before the first frost that ends the growing season. Several astronomical factors involving the earth-moon-sun viewing geometry contribute to making this spectacular late summer (or early fall) event special - a large lunar disk that appears as a pumpkin hanging above the eastern horizon just after sunset for several consecutive evenings.
• Eye on the tropics -- The historic or statistical annual peak in the Atlantic hurricane season occurred over this past weekend (10-12 September), as determined as the date during the entire season with most frequent number of named tropical cyclones (tropical storms and hurricanes), based upon over 100 years of record. This date corresponds closely with the time of peak sea-surface temperatures across those sections of the North Atlantic considered hurricane-breeding areas. [NWS National Hurricane Center] [Note: So far this Atlantic hurricane season, which commenced on 1 June 2011, two tropical cyclones have reached hurricane status, while twelve have were tropical storms. EJH]
• Celebrate International Day for the Preservation of the Ozone Layer -- The United Nations Environment Programme has proclaimed that this upcoming Friday 16 September 2011 to be the International Day for the Preservation of the Ozone Layer, a commemoration of the day in 1987 when nations commenced the signing of the Montreal Protocol to limit and eventually ban ozone-depleting substances such as chlorofluorocarbons (CFCs) and other chlorine and bromine-containing compounds. [United Nations Environment Programme]

• US weather and climate reviewed for August and Summer 2011 -- Based upon preliminary data, scientists at NOAA’s National Climatic Data Center report that the recently concluded meteorological summer of 2011 (June, July and August) was the second warmest summer across the coterminous United States since sufficiently reliable climate records began in 1895. Texas, Oklahoma, New Mexico, and Louisiana had their warmest (June-August) summers on record. In fact, the statewide average summer temperatures for both Texas and Oklahoma exceeded the all-time seasonal temperature for any state in any season that had been set by Oklahoma in the summer of 1934. The nationwide temperature for August 2011 was only 0.1 Fahrenheit degrees below the warmest August on record; this monthly average temperature that was 3.0 Fahrenheit degrees above the 20th century (1901-2000) average.
  The nationwide August 2011 average precipitation was slightly (0.29 inches) below the 20th century average, while the nationwide summer precipitation was 1.0 inch above this average. Texas had its driest summer on record, with a statewide average of 2.44 inches of rain, which was 1.04 inches less than the previous driest summer in 1956. On the other hand, New Jersey and California had their wettest summers on record. [NOAA News]

• Pole-to-pole flights help paint first global portrait of greenhouse gases -- A three-year field campaign called HIPPO (HIAPER Pole-to-Pole Observations where HIAPER stands for High-performance Instrumented Airborne Platform for Environmental Research) ended this past week. This project, which was coordinated by the National Center for Atmospheric Research, involved research flights made from the Arctic to the Antarctic to sample greenhouse gases and aerosols. These flights, which were made at altitudes ranging from 500 feet to 45,000 feet above the Earth's surface, helped produce a detailed three-dimensional map of the global distribution of gases and particles that affect Earth’s climate. [UCAR/NCAR News]
• Data-collecting balloons sent aloft for wind energy project -- During this week, NOAA’s Air Resources Laboratory plans to launch weather balloons from the Duke Energy Ocotillo Wind Farm located near Forsan, TX at two-hour intervals that will carry radiosondes or small instruments designed to collect and transmit wind speed, wind direction, temperature, and relative humidity data. These data will be used to assess the vertical atmosphere structure over the wind farm, which will assist these wind farms in producing renewable wind energy. [NOAA News]
• An All-Hazards Monitor -- This Web portal provides the user information from NOAA on current environmental events that may pose as hazards such as tropical weather, fire weather, marine weather, severe weather, drought and floods. [NOAAWatch]
• Global and US Hazards/Climate Extremes -- A review and analysis of the global impacts of various weather-related events, including drought, floods and storms during the current month. [NCDC]

• A switch from coal to natural gas would not significantly slow climate change -- Computer simulations conducted by a senior atmospheric researcher at the National Center for Atmospheric Research indicate that a change from the burning of coal to natural gas, which emits less carbon dioxide, would not significantly slow changes in climate attributed to human activity. As part of the simulation, the contribution that the leakage of methane from natural gas contributes to increased global air temperatures was also considered. [UCAR/NCAR News]
• Clouds appear to amplify climate change -- An atmospheric science professor from Texas A&M University claims that clouds serve only to amplify changes in climate through "feedback" mechanisms rather than initiating climate change. His findings are based upon his study of the planetary energy budget together with rhythmic El Niño and La Niña events over the past 10 years. [LabSpaces] [You Tube]
• Hurricane landfall threat probabilities and climate variability revealed -- Scientists at the University of Miami’s Rosenstiel School of Marine & Atmospheric Science who studied the Atlantic hurricane records between 1950 and 2010 have determined a relationship between hurricane tracks and climate variability, such as those involving El Niño and La Niña events. [University of Miami’s Rosenstiel School of Marine & Atmospheric Science]

• Studying air travel of microbes could be beneficial -- Researchers at Virginia Tech have been developing a new "aerobiological" modeling technique that involves the study of the travel of microbes in the atmosphere. The scientists hope that their research can be applied to the dispersion of these microbes and help in the monitoring of the spread of disease, crop security and changes in climate. [Virginia Tech]

• La Niña returns -- Last week, forecasters with NOAA's Climate Prediction Center upgraded their La Niña Watch to a La Niña Advisory based upon their analysis of the patterns of average sea surface temperatures (SST) across the tropical Pacific Ocean during the previous week. These SST anomalies (differences between observed and long-term average SSTs for the week) revealed below normal temperatures across the eastern tropical Pacific, which would indicate re-emergence of a La Niña event, an anomalous atmospheric and oceanic circulation regime that contributed to extreme weather around the globe during the first six months of 2011. The researchers foresee a gradual strengthening of the La Niña event through Northern Hemisphere fall and into winter. [NOAA News]
• Extreme summertime temperatures could become a regular occurrence -- Researchers at Boston University warn that the projected near-term increases in global mean temperature by 2 Celsius degrees would result in summertime temperatures across the US and elsewhere that would exceed observed historical extremes in at least half of all years. [LabSpaces]

• Tree ring analysis reveals centuries old forest fires -- A researcher at Texas A&M University describes his use of tree ring analysis to study the fire history of forests across the southern and central Appalachian Mountains over the last 300 to 400 years. He notes that fires across the region have decreased dramatically since the 1930s, following increased public awareness campaigns by various agencies such as the US Forest Service. [Texas A&M University TAMUtimes]
• Episodes of abrupt climate variability found during last 800,000 years -- An international team of researchers who reconstructed an 800,000 year climate record from ice cores extracted from the Greenland ice sheet report that the planetary climate has undergone very rapid transitions during this time span. [Cardiff University News Centre]
• Evidence of ancient iron-rich oceans helps change views of Earth's early history -- Researchers at the University of California, Riverside and colleagues from Canada, Australia, and China have found evidence in rock samples from around the world for an iron-rich ocean between approximately 1.8 billion and 800 million years ago, which helps modify previously held views of the evolution of early life on Earth. During these times, the ancient deep ocean was nearly devoid of free oxygen, but rich in iron, a key biological nutrient. [University of California, Riverside Newsroom]

• Public highly satisfied with National Weather Service -- In a recent public option survey conducted by an independent survey firm, the public rated NOAA's National Weather Service within the top 15 percent of federal agencies for customer satisfaction. The survey asked respondents to rate National Weather Service performance in the areas of routine climate, water and weather forecasts and services, dissemination services, support services, and severe weather awareness outreach. [NOAA News]
• Hail and severe storms risk management initiative launched -- During the last week, a collaborative weather risk management initiative between NOAA's Atmospheric and Environmental Research and the NOAA National Severe Storms Laboratory was announced that would aid the insurance industry anticipate and react to storm damage. [NOAA News]
• Website for human dimensions of climate change -- An interagency effort within the US federal government that included NOAA, the Bureau of Land Management and the US Forest Service, has resulted in a website called HD.gov (for HumanDimensions.gov) that provides users, such as natural resource managers, with information on the human dimensions on a variety of topics of interest such as climate change. [HD.gov]
• Earthweek -- Diary of the Planet [earthweek.com] Requires Adobe Acrobat Reader.

Concept of the Week: Feedback in Earth’s Climate System

In Earth’s climate system, feedback consists of a process where a change in one variable interacts with other variables of the system to alter that original variable. If the change reinforces the original quantity, it is known as a positive feedback. If the change suppresses the original quantity, it is a negative feedback. Feedbacks in Earth’s climate system are significant—thought to be responsible for more than half the global warming expected from human activities.

Consider examples of positive and negative feedback. A warming trend in climate is likely to accelerate the rate of melting of snow and ice, producing more bare ground that absorbs more solar radiation, further raising the air temperature. A cooling trend prolongs snow and ice cover in spring and summer so that less solar radiation is absorbed, more reflected to space, bringing about additional cooling. In both cases, feedback is positive because the initial change in temperature is amplified.

Consider an example of negative feedback. While feedbacks among temperature, cloud cover, and radiation are not well understood and depend upon circumstances (e.g., type and height of clouds), they could be either positive or negative. It is thought that a warming trend in climate should increase the rate of evaporation of water from Earth’s surface and thereby increase low cloud cover. A thicker and more extensive low-cloud cover reflects more solar radiation to space thereby inhibiting a further rise in surface temperature. Hence, this negative feedback would dampen the initial temperature change.

Understanding feedback in the climate system is essential for modeling and predicting climate change. If some agent or mechanism alters the climate, then feedback may either amplify (positive feedback) or dampen (negative feedback) the change in climate. As demonstrated later in this course, many agents and mechanisms can bring about climate change (e.g., variations in solar energy output, regular fluctuations in Earth-Sun geometry). While these climate forcing agents and mechanisms drive climatic change, processes within the planetary climate system involving feedbacks significantly impact the magnitude of climate change.

Overall, which type of feedback prevails in Earth’s climate system, positive or negative? A system in which positive feedback prevails is unstable. For Earth, this would move the climate regime toward an extreme characterized by excessive cold that would encase the planet in snow and ice ("snowball" or "ice ball" Earth) or toward the other extreme resulting in much higher temperatures—the product of a runaway greenhouse effect. Although Earth’s climate has varied considerably over the billions of years that constitute geologic time, it appears likely that Earth’s climate system has been nearly stable with negative feedbacks generally compensating for positive feedbacks.

Concept of the Week: Questions

Place your responses on the Chapter Progress Response Form provided in the Study Guide.

1. The magnitude of a climate change [(largely depends upon)(is independent of)] positive and negative feedback phenomena operating in Earth’s climate system.
2. Through much of Earth history, it appears that [(positive feedbacks)(negative feedbacks)(a general balance between positive and negative feedbacks)] have (has) prevailed.

• 12 September 1987...Peak sustained winds in Hurricane Max reached 155 mph, the highest observed for an Eastern Pacific hurricane. (The Weather Doctor)
• 13 September 1922...The temperature at El Azizia in Libya soared to 136 degrees to establish a world record at a surface weather station. To make matters worse, a severe ghibi (dust storm) was in progress. (The Weather Channel) (NCDC)
• 13 September 1988...Hurricane Gilbert smashed into the Cayman Islands, and as it headed for the Yucatan peninsula of Mexico strengthened into a monster hurricane, packing winds of 175 mph. The barometric pressure at the center of Gilbert reached 26.13 inches (888 mb), an all-time record for any hurricane in the Caribbean, Gulf of Mexico, or the Atlantic Ocean. Gilbert covered much of the Gulf of Mexico, producing rain as far away as the Florida Keys. (The National Weather Summary) (Storm Data)
• 14 September 1937...The mercury soared to 92 degrees at Seattle, WA, a record for September. (The Weather Channel)
• 14 September 1970...The temperature at Fremont, OR dipped to 2 degrees above zero to equal the state record for September set on the 24th in 1926. (The Weather Channel)
• 14 September 1987...Barrow, AK received 5.1 inches of snow, a record for September. (Sandra and TI Richard Sanders - 1987)
• 14 September 1988...Pressure in the eye of Hurricane Gilbert moving across the Caribbean Sea fell to 885 millibars (26.17 inches of mercury), the lowest recorded barometric pressure in the Western Hemisphere. Ultimately, 318 died in seven countries across the Caribbean and Gulf of Mexico.
• 15 September 1939...The temperature at Detroit, MI soared to 100 degrees to establish a record for September. (The Weather Channel)
• 15 September 1982...A snowstorm over Wyoming produced 16.9 inches at Lander to establish a 24-hour record for September for that location. (13th-15th) (The Weather Channel)
• 16 September 1881...Iowa's earliest measurable snow of record fell over western sections of the state. Four to six inches was reported between Stuart and Avoca. (The Weather Channel)
• 16 September 1964...The temperature at Concord, NH dropped to 27 degrees ending the shortest growing season on record (100 days). (Intellicast)
• 16 September 1988...Hurricane Gilbert made landfall 120 miles south of Brownsville, TX in Mexico during the early evening. During its life span, Gilbert established an all-time record for the Western Hemisphere with a sea-level barometric pressure reading of 26.13 inches. Winds approached 200 mph, with higher gusts. Gilbert devastated Jamaica and Mexico's Yucatan Peninsula. (The National Weather Summary) (Storm Data) (The Weather Channel)
• 16 September 2004, Birmingham, Alabama: Birmingham, AL set two all-time records for the city as Hurricane Jeanne crossed the city: Lowest sea level pressure on record, 986.8 millibars (29.14 inches of mercury), and the greatest 24-hour rainfall event on record, 9.75 inches. (The Weather Doctor)
• 17 September 1829...The Siebold Typhoon, Japan's most catastrophic typhoon, inflicted widespread damage over much of Japan. On the southern island of Kyushu, the storm surge off the Ariake Sea kills 10,000. (The Weather Doctor)
• 17 September 1932...Westerly, RI received 12.13 inches of rain, which set a 24-hour precipitation record for the state. (NCDC)
• 17 September 1963...Nearly 2.5 inches of rain fell in 24 hours, the most intense rain for Yuma, AZ during the period between 1909 and 1977. (The Weather Doctor)
• 18 September 1991...2.4 inches of snow fell at Duluth, MN to set a new record for September. (Intellicast)

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Prepared by Edward J. Hopkins, Ph.D., email hopkins@meteor.wisc.edu
© Copyright, 2011, The American Meteorological Society.