FESSTVaL experiment — week 12 and 13

Researchers from the Uni­ver­si­ty of Cologne were the PIs in charge of the FES­ST­VaL cam­paign on the first 2 weeks of August (weeks 12 and 13 from the total cam­paign):

Dur­ing the 12th week of the Dr. Eduar­do Wei­de Luiz was the PI. The week was full of false alarms and no strong pre­cip­i­ta­tion hap­pened in Lin­den­berg. The rain insist­ed in avoid­ing the region, even with the pres­ence of a frontal sys­tem pass­ing by. There was only a bit of rain and some weak­er cold pools, but it was a week of not so many inter­est­ing mete­o­ro­log­i­cal events over the FES­ST­Val site

s. The region around, how­ev­er, was affect­ed by some stronger rain show­ers, which indi­rect­ly affect­ed the tem­per­a­ture at the sites, but with no asso­ci­at­ed mea­sured rain.

Inter­est­ing­ly, two noc­tur­nal low lev­el jets events hap­pened, one relat­ed to a cold pool and anoth­er to the noc­tur­nal tem­per­a­ture inver­sion. In addi­tion, Sun­day was rel­a­tive­ly inter­est­ing for the gust’s enthu­si­asts, with winds above 10 m/s at 10 m height. Unfor­tu­nate­ly, this week was not good for extra mea­sure­ments, like the launch of some radioson­des.

Shal­low con­vec­tion on 31 July

Week num­ber 13 had as PI Dr. Stephanie Fiedler and was not as unlucky as the pre­vi­ous week. Two impres­sive cold pools at the begin­ning of the week were mea­sured. Both were poor­ly fore­cast­ed by numer­i­cal weath­er pre­dic­tion mod­els and char­ac­ter­ized by sharp tem­per­a­ture reduc­tions, the onset of rain­fall, and an increase in near sur­face wind speed. Cold pool ‚Frank‘ on Mon­day and ‚Stephanie‘ on Tues­day came to the FES­ST­VaL site in the late evening around 22:00 local time. The event on Tues­day ini­tial­ly approached the sites direct­ly from the West and turned slight­ly north­ward just before enter­ing the mea­sure­ment net­work. It was pos­si­ble to wit­nessed light­ning and a beau­ti­ful anvil of the sys­tem, as shown below.

The rest of the week was com­pa­ra­bly calm, dry, and warm due to a semi-sta­tion­ary high-pres­sure sys­tem that deter­mined the local weath­er con­di­tions. Large­ly cloud-free con­di­tions led to ide­al con­di­tions for the devel­op­ment of a sta­bly strat­i­fied noc­tur­nal bound­ary lay­er in two con­sec­u­tive nights, mon­i­tored with addi­tion­al radiosonde launch­es around 21 and 03 UTC. The sur­face inver­sion in the first night was unusu­al­ly strong for this time of the year. We have seen noc­tur­nal low-lev­el jets, although with rel­a­tive­ly low wind speeds in their jet core due to the weak hor­i­zon­tal pres­sure gra­di­ent. Increased aerosol bur­den towards the end of the week caused scenic sun­sets (see below). It has also allowed to take inter­est­ing day­time mea­sure­ments of the aerosol opti­cal depth with a new sun­pho­tome­ter acquired by UoC that will be com­pared to the instru­ments installed at the radi­a­tion cen­tre of DWD in Lin­den­berg. Even Fri­day the 13th of this week there­fore was a lucky day with inter­est­ing weath­er and an aerosol plume pass­ing the site — a great end just before a calm, sun­ny, and warm sum­mer week­end.