Red sky in Goiás is caused by dust and pollutants in dry air

The reddish sky that has attracted attention in Goiás at this time of year is caused by an optical effect enhanced by the dry climate. The phenomenon happens when sunlight breaks at dawn or sunset and hits dust particles and pollutants accumulated in the air, André Amorim, manager of the Goiás Meteorological and Hydrological Information Center (Cimehgo), told g1.

"When colliding with this dust, the light takes on this reddish or orange tone, creating a very striking visual effect, which gives the impression that the horizon is on fire," said André.

For Elisabete Alves, coordinator of the National Institute of Meteorology (Inmet), the reddish tone is linked to the prolonged drought in the state. Without rain for months, soil moisture drops drastically, leaving the earth loose and making it easier to lift dust.

Wind currents known as "low-level jets", the same atmospheric routes responsible for carrying moisture from the "flying rivers" from the North to the Central-West, bring smoke and soot originating from fires in the Amazon and Mato Grosso, overloading the Goiás atmosphere with aerosols, according to Elisabete.

Find out why the sky turns red in Goiás at this time of year — Photo: Wesley Costa/O Popular

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Cold fronts

According to Elisabete, the instability caused by the passage of cold fronts during the beginning of spring induces rain showers capable of "washing" the atmosphere, settling dust and soot in suspension, in addition to alleviating the heat and occasionally raising the air humidity levels.

As it is a transition period between drought and the wet cycle, the beneficial effects of these cold fronts are temporary. After the rain ends, the dry air mass returns to predominate over the state, causing temperatures to rise and the air to dry out again until the next rains.

Wave blocking

The director of the Plêiades do Sul astronomy club, Ary Martins, said that, with the air saturated with pollutants, the passage of light is even greater blocked. The excess of solid particles not only retains the short waves, but also blocks and scatters the longer wavelengths, corresponding to orange and red.

It is this direct interference with the larger waves, according to Ary, that increases the dispersion of warm colors, resulting in the orange aspect that dominates the landscape.

"At dusk, the sun's rays travel through a larger section of the atmosphere and the shorter blue wavelengths are already naturally dispersed. With many suspended particles, the blocking of the waves affects not only the short waves, but also the longer ones, associated with orange and red, spreading these colors and intensifying the red sky", he highlighted.

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