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Evaluation of the ASOS impact on climatic normals and assessment of variable-length time periods in calculation of normals

Chad Matthew Kauffman, University of Nebraska - Lincoln


The temperature and precipitation that describe the norm of daily, monthly, and seasonal climate conditions are “climate normals.” They are usually calculated based on climate data covering a 30-year period, and updated in every 10 years. The next update will take place in year 2001. Because of the advent of the Automated Surface Observations Systems (ASOS) beginning in early 1990s and recognized temperature bias between ASOS and the conventional temperature sensors there is an uncertainty of how the ASOS data should be used to calculate the 1971–2000 temperature normal. This study examined the uncertainty and offered a method to minimize it. It showed that the ASOS bias has a measurable impact on the new 30-year temperature normal. The impact varies among stations and climate regions. Some stations with a cooling trend in ASOS temperature have a cooler normal for their temperature, while others with a warming trend have a warmer normal for temperature. These quantitative evaluations of ASOS effect for stations and regions can be used to reduce ASOS bias in temperature normals. ^ This study also evaluated temperature normals for different length periods and compared them to the 30-year normal. It showed that the difference between the normals, is smaller in maritime climate than in continental temperate climate. In the former, the six-year normal describes a similar temperature variation as the 30-year normal does. In the latter, the 18-year normal starts to resemble the temperature variation that the 30-year normal describes. These results provide a theoretical basis for applying different normals in different regions. ^ The study further compared temperature normal for different periods and identified a seasonal shift in climate change in the southwestern U.S. where the summer maximum temperature has shifted to a late summer month and the winter minimum temperature shifted to an early winter month in the past 30 years. ^

Subject Area

Physical Geography|Physics, Atmospheric Science

Recommended Citation

Kauffman, Chad Matthew, "Evaluation of the ASOS impact on climatic normals and assessment of variable-length time periods in calculation of normals" (2000). ETD collection for University of Nebraska - Lincoln. AAI9997011.