Dust that lifted from a dry Patagonian lake and reached the Atlantic could be seen on various satellite images in March 2020.
24 January 2022
06 March 2020
By HansPeter Roesli (Switzerland)
Patagonia is the only landmass exposed to southern westerlies and within the region there is a semi-dry lake, Colhué Huapí, which is a major dust source.
Lake Colhué Huapí is situated inland around 100 km northwest of Comodoro Rivadavia on the Atlantic coast and 300 km to the east of the southern section of the Andes. The lake, which covers a shallow depression, has a pronounced annual level cycle which changes from high (2 m deep) after the snow-melt, to dry in the warm season. For comparison the nearby Lake Musters has water all year round.
Figure 1 shows the two extremes of the last annual cycle: blue-water in August 2019, brown-dry in March 2020. Comparing the August 2019 state to this annotated satellite image shows that in 2019 the lake did not reach its maximum extent.
Subjective day-by-day inspection between January 2019 and May 2020 of visible MODIS/VIIRS imagery on NASA’s World View (https://worldview.earthdata.nasa.gov/) revealed that for the majority of the time the areas around the lake and east of it were shrouded in faint dust from the dry parts of the lake. Also, every month or so stormy westerlies lifted more dust than usual and spread it over the adjacent Golfo de San Jorge.
Dust events 2019-2020
List of dust outbreaks where dust streaks were well visible over the Golfo de San Jorge, subjective inspection of True Color RGBs from MODIS/VIIRS on WorldView .
2019: 28 Jan, 19 Feb, 17 Mar, 12 May, 17 & 18 May, 26 Jul, 26 Aug, 29 Sep *, 31 Oct, 03 Nov, 06 Nov, 15 Nov, 17 Nov, 18 Dec *
2020: 14 Jan, 25 Jan, 03 Feb, 14 & 15 Feb *, 07 Mar *, 04 Apr, 16 May
*major outbreaks with strong dust signal over water
In the warm season between October 2019 and March 2020, four of these events (marked with an asterisk) produced particularly dense and long dust streamers that reached over and into the South Atlantic.
On 7 March 2020 at 18:56 UTC a crew member on the International Space Station (ISS) took a photo of one such event, Figure 2 compares the ISS photo with a True Color RGB from GOES-East data, observed around the same time. For better comparison the ISS photo was rotated in order to have the dust streamers aligned with those on the GOES image. Obviously, the ISS photograph has better spatial resolution. It shows several distinct dust streamers taking off over the dry Lake Colhué Huapí (under two cloud banks on the left-hand ISS image border). Due to the very different points of observation (ISS from south-west at 400 km altitude, GOES-East from north at 36’000 km altitude) the dust streamers were sightly shifted north and southward with respect to the background.
Some of the streamers on the ISS photo were already visible in the early local morning at 13:08 UTC on a True Colour RGB from OLCI on Sentinel-3B (Figure 3).
In the following night, one day from full Moon on 8 March at 05:10 UTC, the Day-Night Band (DNB) on NOAA-20 saw a dust plume straddling the 60°E longitude, some 700 km from its origin (Figure 4). The arched light-grey veil compares well to the pink dust signal on the adjacent Dust RGB image from GOES-East. The two clusters of lights to the south of the dust arc were most probably from fishing boats.
On 7 March the dust was lifted in the back of a deep depression (central pressure less than 964 hPa), centred just south of the Terra del Fuego (Figure 5). It influenced gale-force westerly winds across the Patagonian steppe, in the lee of the moderately high southern section of the Andes along the Chilean coast (Foehn effect).
In the area of interest the GFS analysis of the wind field at 18:00 UTC (Figure 6) indicated wind speeds of 40 kt to 50 kt at 950 hPa. Between 15:00 UTC and 17:00 UTC the METAR messages from the coastal Comodoro Rivadavia Aerodrome (SAVC, 87860) reported drifting dust with horizontal visibility down 5 km/3 km and wind gust up to 40 kt.
RGB image sequences from GOES-East show the evolution of the dust outbreak. The GOES-16 True Color RGBs (Figure 7) zoom in on the gulf area and the first hours of the event that started right after day break.
On the Dust RGBs (Figure 8) the dust veil may be followed up to its ingestion into the depression that, at the end of the animation at 03:00 UTC on 8 March, had moved from Terra de Fuego towards the Weddell Sea.
By that time the dust head had travelled at least 1000 km eastward, which corresponds to an average speed of 45 kt over 12 hours, well in line with the analysed winds shown above.
Dust RGBs at six-hour intervals between 7 March 06:00 UTC and 8 March 12:00 UTC (Figure 9) give an idea of the event at synoptic scale.
On both animations (Figures 7 and 8) transient banks of altocumuli lenticularis stayed stationary over the coastal area. They signalled the presence of standing waves in a laminar atmosphere. NASA’s Earth Observatory website reported on a similar event in May 2013 .
Other South American dust cases
Dust from Africa travels to Brazil
Typically, every year between June and August dust travels across the Atlantic, as shown in this Meteosat-10 imagery.
Smoke & dust streamers over Argentina seen by Meteosat-10
Strong winds, high temperatures, and months of drought fuelled an outbreak of wildfire in northern Argentina in September 2013.
Dust squall (haboob) over Argentina
Dust squall (haboob) over Argentina causes fatal road accidents.
Zonda wind carries dust across Bolivia & Argentina
Example of the viento blanco and viento zonda carrying large amounts of dust across Bolivia and Argentina.
Latest case studies
Chalane crosses southern African subcontinent
Tropical Storm Chalane landfall in Madagascar and Mozambique in December 2020 then crossed the entire South African subcontinent.
Early summer convection in Argentina & Uruguay
Severe convection in central Argentina in December 2020.
Pacific cirrus above stratocumulus
New NIR1.3 channel on GOES ABI helps to detect thin cirrus clouds above low-level clouds.
Nearly-record snowfall in the western Alps
Winter 2020 started with more than 2 m snow in the Alps and an extreme amount of rain.
Upwelling in the Gulf of Tehuantepec
Strong upwelling of cold ocean waters and an increase in phytoplankton growth in the Gulf of Tehuantepec.