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Category Archives: Seasons
Each winter we keep track of the areal extent of air colder than 23 degrees Fahrenheit at the 850 mb pressure level (about 1 mile above sea-level) around the entire Northern Hemisphere. This measure allows us to characterize the intensity of the winter season with respect to the lower tropospheric temperature.
Over the past 75 seasons there has been a systematic decrease in the December-January-February, or DJF, average areal extent of about 4.6%, and this is an unequivocal sign of global warming, measured in the winter season. Continue reading
The U.S. National Climate Assessment is mandated by the Global Change Research Act of 1990. The assessment is conducted about every four years and is an authoritative scientific analysis of climate change risks, impacts and responses in the U.S.
The nation this month completed the Fifth National Climate Assessment, or NCA5. The National Oceanic and Atmospheric Administration is the administrative agency for NCA5 and certifies that the report meets Information Quality Act and Evidence Act standards. The assessment is an extensive process that includes internal and external review from federal agencies, the general public and external peer review by a panel of experts. Continue reading
The surface waters of our polar oceans freeze seasonally, forming a layer of sea ice that varies in thickness from centimeters to meters. The era of polar orbiting satellites has enabled the monitoring of sea ice distribution for more than four decades.
Seasons are reversed between the Northern and Southern hemispheres, so the sea ice maximum and minimum occur at different times of the year. Generally speaking, around mid-September the extent of the sea ice at the south pole is reaching a maximum, while in the Arctic it is approaching a minimum in September as our Northern Hemisphere summer comes to an end. Continue reading
As we enter the month of October and the traditional end of the warm season, it’s interesting to note that the average temperature last month, through Sept. 28, was 4.0 degrees above normal in Madison.
That is by far the biggest deviation among traditional warm-season months — June, July, August and September. All were warmer than average this year: June was 0.8 degrees, July just 0.5 degree and August only 1.2 degree above the respective norm. Continue reading
This year, the autumnal equinox occurred on Saturday, Sept. 23, at 1:50 a.m. Central Time. During the equinox, the sun shines directly on the equator as its position moves from one hemisphere to the other. The word “equinox” is derived from the Latin word “aequus,” which means “equal,” and “nox,” which is the Latin word for “night.” During the 24 hours of the equinox, there are about 12 hours of day and 12 hours of night.
You may hear that daylight and nighttime are of equal length on the equinox. But during the equinox at our midlatitude location, there are approximately eight more minutes of daylight for two reasons: the sun’s shape and atmospheric refraction. Continue reading