Record high solar irradiance in Western Europe during first COVID-19 lockdown largely due to unusual weather

Pub­lished in Com­mu­ni­ca­tions Earth & Envi­ron­ment, Vol­ume 2, 37, 2021:

Spring 2020 broke sun­shine dura­tion records across West­ern Europe. The Nether­lands record­ed the high­est sur­face irra­di­ance since 1928, exceed­ing the pre­vi­ous extreme of 2011 by 13%, and the dif­fuse frac­tion of the irra­di­ance mea­sured a record low per­cent­age (38%). The coin­cid­ing irra­di­ance extreme and a reduc­tion in anthro­pogenic pol­lu­tion due to COVID-19 mea­sures trig­gered the hypoth­e­sis that clean­er-than-usu­al air con­tributed to the record. Based on analy­ses of ground-based and satel­lite obser­va­tions and exper­i­ments with a radia­tive trans­fer mod­el, we esti­mate a 1.3% (2.3 W m⁻²) increase in sur­face irra­di­ance with respect to the 2010–2019 mean due to a low medi­an aerosol opti­cal depth, and a 17.6% (30.7 W m⁻²) increase due to sev­er­al excep­tion­al­ly dry days and a very low cloud frac­tion over­all. Our analy­ses show that the reduced aerosols and con­trails due to the COVID-19 mea­sures are far less impor­tant in the irra­di­ance record than the dry and par­tic­u­lar­ly cloud-free weath­er.

Authors: Chiel C. van Heer­waar­den, Wouter B. Mol, Men­no A. Veer­man, Imme Bene­dict, Bert G. Heusinkveld, Wouter H. Knap, Ste­lios Kazadzis, Natalia Kouremeti and Stephanie Fiedler

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