Climatic Thought: The Time Period Between Weather and Climate

Keywords: climatic thought, weather regimes, macroweather, subseasonal
Session Type: Virtual Paper
Day: Saturday
Session Start / End Time: 4/10/2021 08:00 AM (Pacific Time (US & Canada)) - 4/10/2021 09:15 AM (Pacific Time (US & Canada))
Room: Virtual 24

Abstract

An important conceptual distinction in the atmospheric sciences is the difference between weather and climate. It is well known that the current or short-term state of the atmosphere is different from the accumulation of conditions over some more lengthy time period. The AMS glossary suggests that the time period for climate is a month or more. Based on the quality of initial observations and character of the atmosphere, a successful deterministic weather forecast can extend to at least ten days. Due to the chaotic nature of the atmosphere, prediction for more lengthy time windows, as is done by the Climate Prediction Center, tends to rely on successful understanding of boundary conditions and how those conditions might shift during the coming weeks (or longer).
What is the shortest time window that one might call a climatic time period? Was Lorenz correct that this boundary is shorter than a month? This contribution to the development of climatic thinking looks at the fuzzy temporal boundary between weather and climate and some of the ideas that address this fuzzy temporal boundary. Concept development builds from early efforts that examined spells, Lamb weather types, and Grosswetterlagen. Extending from 10 days to three months, the character of the atmosphere during this time window has been labeled several different ways including: primary singularities, weather regimes, periods of blocking, macroweather, and subseasonal-to-seasonal. This review compares and contrasts the character and rationale used to establish these similar but different atmospheric constructs.