Please note that I wrote "weather observations", not "weather" per se :-)
I'm just finishing up processing all the 2020 weather data from NCEI's ISD (National
Center for Environmental Information Integrated Surface Database), which has become a
ritual for me every January for the past decade.? When I got to processing the data for
East Asia, I was puzzled initially to get only 64 usable weather files for China, instead
of the usual 400, and? even fewer for Japan.? When I looked in the metadata, I found? this
was due to the absence of Cloud Cover information I need to calculate the solar
radiation.? Attached is a table showing the number of cloud cover reports by month,
followed by the annual average, for all ISD stations in China and Japan for 2020.
I was startled when I first looked at this table.? In China, 80% of the weather stations
all stopped reporting cloud cover in April.? In Japan,? the dropoff was even greater,
although not as uniform as in China, with many stations not reporting Cloud Cover
throughout the year,? many others stopping in February or March, leaving only 21 stations
(8%)? that had Cloud Cover data? for the entire year.
I can't find any reasonable explanation for this change except for the lockdowns due to
the pandemic.? Although weather stations have become automated everywhere, Cloud Cover
reports are still based on human observation, excepting those ASOS (Automated Surface
Observing System) stations equipped with? upward-looking lasers and ceilometers. I've
noted two years ago that Cloud Cover data have been dropping steadily in recent years (see
attached e-mail "Decline of cloud cover report in the ISD"), but what's happened? this
time in China and Japan clearly has a very different cause.? All the more reason to move
to satellite-derived solar radiation !
Joe
--
Joe Huang
White Box Technologies, Inc.
346 Rheem Blvd., Suite 205A
Moraga CA 94556
yjhuang at whiteboxtechnologies.com
http://weather.whiteboxtechnologies.com for simulation-ready weather data
(o) (925)388-0265
(c) (510)928-2683
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