summer weekday effect: industry heats up Tokyo, moistens U.S.
Two recent studies have shed new light on how the Monday-to-Friday
focus of urban work life helps shape local and regional climate.
In Japan, a group of university and federal scientists has found
that waste heat from air conditioning appears to be raising air
temperatures by at least 1–2°C on summer weekdays in
office-dense parts of Tokyo. Led by Yukitaka Ohashia (Okayama University
of Science), the team employed a multilayer model of urban areas—including
buildings and the “canyons” between them—and
a building energy-analysis model. This work was supplemented by
four days of observations from central Tokyo. Although the model
simulated nighttime temperatures well, it was unable to replicate
the observed weekday readings at ground level unless it factored
in the heat generated by air conditioners at rooftop level (about
36 meters or 120 feet).
For the southeast United States and nearby waters, Thomas Bell
(NASA) and colleagues found a distinct weekly cycle in summer precipitation
as detected by the Tropical Rainfall Measuring Mission satellite
from 1998 to 2005. The average coverage and duration of afternoon
showers and thunderstorms were more than 40% greater over land
areas on weekdays than on weekends, and more than 40% more of the
land-based thunderstorms grew to altitudes greater than 9 kilometers
(5.6 miles) from Tuesday to Thursday than from Saturday to Monday.
Bell and colleagues are now examining longer-term rainfall records
prior to 1998. Daniel Rosenfeld (Hebrew University of Jerusalem)
hypothesizes that the increased aerosol pollution on weekdays produces
a larger number of smaller droplets that rise to greater heights,
stimulating more ice-phase activity and more energetic thunderstorms. “It
will take modeling to sort all this out,” said Bell
at the American Meteorological Society’s annual meeting in
San Antonio, where he presented the work on 18 January.