So-called squall lines frequently bring thunderstorms to the Amazon region, with impacts on surface meteorology and CO2 fluxes.
The atmosphere in tropical regions contains a lot of moisture in the form of water vapor. As a result, thunderstorms with heavy precipitation are prevalent. But these thunderstorms do not only bring a lot of rain. They often come with heavy, turbulent winds such as wind gusts. While the rain is important in providing water to the ecosystem, the turbulent winds also have important effects. Without turbulence, there would be little to no exchange of gases and particles between the forest canopy and the atmosphere above, as well as between distinct atmospheric layers. This is important for CO2 exchange and plant transpiration, but also for the structure of the forest. As a result, cloud formation and precipitation, as well as plant productivity and finally food production are impacted by turbulent air movement common in thunderstorms.
In the Amazon, such thunderstorms tend to occur along long lines spanning many hundreds of kilometers. They are initiated by ocean breeze from the Atlantic Ocean and are visible even from space. These so-called squall lines frequently travel long distances and eventually pass over the ATTO site.
© angepasst von den Geostationären Operationellen Umweltsatelliten (GOES-13-Satellit), die vom Zentrum für Wettervorhersage und Klimastudien (CPTEC/INPE: satelite.cptec.inpe.br/acervo/goes.formulario.logic) bereitgestellt werden
Marcos Gonçalves from the Federal University of Para and his colleagues now set out to analyze the occurrence of squall lines. They wanted to see what their impact on the turbulent exchanges near the surface is. The team used satellite images of the central Amazon region to identify the occurrence of squall lines. In 2014 they counted 12 and in 2015 14 squall lines.
In the next step, they looked at turbulence data and surface parameters from the ATTO site during the times when the squall lines passed over the ATTO site according to the satellite images. They noted that squall lines affect many variables near the surface:
- increase in precipitation rates, wind speed and relative humidity
- decrease in air temperature, shortwave radiation, sensible and latent heat flux
- the CO2 flux reversed its sign
While thunderstorms and squall lines had been studies before, scientists typically performed case studies of a single event. This is the first study to show the consequences of the presence of squall lines on surface exchanges over such a long two-year period. The results will be helpful to improve models of atmospheric chemistry and thermodynamics. Consequently, these insights can help to enhance and develop better forecasts of Amazonian weather and climate.
Gonçalves et al. published the study “Squall lines and turbulent exchange at the Amazon forest-atmosphere interface” in the journal Meteorology and Atmospheric Physics.
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