This is an update on the currently observed huge footprint of the Australian bushfires in the atmosphere over Punta Arenas. Already since several days we are observing an astonishingly high aerosol load over Punta Arenas. The sky during dawn and dusk remains in purple-orange lights produced by the illuminated stratospheric smoke plumes (photo taken by Cristofer Jimenez):

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The aerosol signatures are well observed by our lidar system PollyXT, which is - let's keep fingers crossed for the future - currently working well in documenting the evolution of the smoke plume over our DACAPO-PESO field site at University of Magallanes. That's actually a new job for the system which it serves already since mid of November 2019, when first tropospheric plumes of the Australian fires arrived over Punta Arenas. Before, the Polly lidar was deployed to provide primarily information about the microphysical structure of clouds in the presumably aerosol-free troposphere over Punta Arenas.

On 28 January, the Australian smoke aerosol spreads from the near surface up to 26.5 km height.

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And the smoke plume is still rising. This is likely caused by radiative heating of the plume that leads to an upward motion. At least the original injection height of the smoke by the fires and pyrocumulonimbus activity in Australia cannot explain such extraordinary layer heights.

Aerosol optical depth of the main layer (22 – 26 km) is 0.22 @ 532 nm wavelength (for experts: derived with the Klett-Fernald method, lidar ratio=60 sr and smoothing length = 300 m). This means, that only 80% of sunlight reach the Earth’s surface unaffected by scattering – making the sky much more ‘milky’. The normal value down there is 99%.

This fire season will definitely leave a footprint in the southern-hemispheric stratosphere (above approx. 12 km height) for the next months to years.

Find below an impression of how the LACROS field site looks like at night:

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[ps]

It is getting spring in Punta Arenas (yes, two digit maximum temperatures are possible now!).

For one of the instruments this means time to go home. The 94 GHz radar LIMRAD94 from LIM has been turned off and packed on Sep 25.

 

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It has been gathering data non-stop for nearly 10 months and needs some maintenance before it can go onto its next adventure: a ship-borne deployment onboard the RV Meteor at the field experiment (eurec4a) off of the coast of Barbados to study trade-wind cumuli in the beginning of next year. Having radars point exactly to zenith on a ship is of course only possible with a stabilization platform. We will test the newly-built platform at the manufacturer RPG in Germany in October.

Have a save trip, LIMRAD94!

[hk]

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More than three months LACROS has operated more or less unattended in the far south of Chile. In beginning of July, the mid-campaign-maintenance-team arrived. A couple of tasks was rather straightforward and could be done rather quickly, weather permitting. The 95 GHz cloud radar LIMRAD was outfitted with a pair of new radomes (covers that protect the antenna from the environment, but are transparent to radiation with wavelengths of a couple of millimeters) and the microwave radiometer HATPRO was re-calibrated.

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Others required some more fiddling. Measuring the pulse shape of the 35 GHz cloud radar MIRA required an oscilloscope and some disassembly of the scanner on the container roof. Nevertheless, the effort was justified. The pulses are still as fine as they were years ago. The other issue, strange effects in one of the PollyXT lidar channels could be narrowed down, but not be fully resolved yet. Some more equipment for alignment checks needs to be brought to Punta Arenas.

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Winter weather down here is quite variable: rain, snow, sunshine, mid-level clouds, wind and calms everything at quite a rapid pace. More common than during summer time are cyclone centers passing through to the north. At times, these easterly winds likely intensify precipitation by orographic effects.

For the next two and a half months, again a couple of researchers from Leipzig will take care of LACROS onsite at Punta Arenas.

[mr]