It's that time of year when Bengaluru is swept with strong, gusty winds while skies remain cloudy. While newcomers may be confused by the sudden shift in weather, long-time residents have probably heard the term ‘Aashada gaali’ or ‘Aashada winds’ used to explain it. But what exactly is it? Latha Sridhar, a scientist at the India Meteorological Department, Bengaluru, explains, “‘Aashada gaali’ is not a separate meteorological phenomenon but has been recognised in local weather lore for centuries.There is even a saying in Kannada, “Aashada gaalige aane kocchi hoyitu which means even elephants are swept away during the Aashada month’s winds, it roughly coincides with July. It’s a traditional term referring to the characteristic strong, persistent winds.” She adds, “Typically, in the agrarian community, farmers associate these winds with good soil moisture and see it as a sowing season for kharif crops. While in coastal areas, sea conditions are very rough, so fishermen communitiesare impacted.”
For an explanation rooted inscience, we have to look at the prevailing winds over India at this time of the year: the South Westerlies, which bring monsoon rains to Karnataka.“‘Aashada gaali’ is associated with the strengthening of the southwesterly winds’ flow over the Indian peninsula after the onset of the south west monsoon.This happens because of the establishment of a strong pressure gradient – there is high pressure over the southern Indian Ocean while low pressure is formed over northwest India and Pakistan, which causes intensified flow of moisture laden air from the Arabian Sea towards the west coast and interiors of Karnataka,” explains Sridhar.
Part of the South Westerlies is a low jet stream, easily noticed because it flows at a lower level than others, explains Sridhar, saying, “It is formed 1-1.5 kilometres above sea level, much lower than other jet streams like the Subtropical Westerly Jet or the Tropical Easterly Jet, which are formed at high altitudes." These winds, also known as the Somali Jet or Findlater Jet, travel at ‘high speeds reaching 25-40 knots (37to 74 km/h) over the Arabian Sea,’ adds Sridhar, noting that as they flow through the gaps and terrain of the Western Ghats, they maintain the same speeds or reduce a little. Eventually resulting in the approximately 35 km/hr winds we’ve been experiencing in the city. Another thing that makes them stand out in people’s memories is the fact that, unlike thunderstorm winds, they are persistent. “Thunderstorm winds dissipate within half an hour or so, but in this phase, the winds are continuous and accompanied by intensive cloud cover over days or weeks,” says Sridhar.