The abundant rainfall this weekend in the form of torrential showers and strong winds respond to the meteorological phenomenon known as DANA. Its arrival can be foreseen but not its consequences in the form of rain or storms.
It is an isolated atmospheric depression at high levels that is produced by the collision of a cold air mass in height with the warm air from the surface. This phenomenon, traditionally called "cold drop", gives rise to intense showers and storms. Thus, the entry of a mass of cold air into the core of the atmosphere that comes into contact with warmer air near the ground generates instability, which favors the formation of clouds that cause strong storms.
The DANA is formed from the polar jet, a current of very intense winds (between 150 and 300 km/h) that circulates in the upper part of the atmosphere (at an altitude of 9,000 meters) and whose route revolves around the North Pole. and from West to East (from North America to Europe and Russia). This phenomenon moves causing undulations, meanders that circulate around the planet, with time scales of between 7 and 10 days and that are drivers of storms, anticyclones and DANAs.
The State Meteorological Agency (Aemet) explains that a DANA has two types of causes: dynamic (associated with the phenomenon) and thermodynamic (due to the difference in temperatures). In the northern hemisphere and in mid-latitudes, "normally, storms and anticyclones circulate from west to east," but sometimes waves form and "one of the waves forms a kind of cold air pocket and is isolated." with a more erratic movement.”
The erratic movement of the cold air mass "makes it more difficult to predict" its trajectory, according to Aemet. In addition, a DANA "can cause adverse weather, but also high temperatures because, if it is located very far to the west, it generates the entry of a southerly wind and a rise in thermometers". storms; they are favored, but not always.
Aemet recommends using the acronym DANA to refer to this phenomenon, rather than the term "cold drop", which comes from the German school that named it kaltluftropfen. The Foundation for Urgent Spanish points out that the cold drop is produced by the entry of “an air mass that is released from a very cold current” and that when it descends on hot air “it produces great atmospheric disturbances.”
Extreme weather events are increasing due to the impact of climate change. It is not that DANA is produced by climate change, but rather that it contributes to an increase in DANAs and very possibly an increase in the virulence of precipitation.
In a country like Spain, the influence of sea temperature on the formation of DANAs is essential to understand this process. The Mediterranean Sea offers this necessary ingredient for the formation of strong storms and heavy rains. Its hottest waters at the end of summer act as a trigger mechanism for storms and torrential rains when a DANA arrives. This makes it easier for stormy clouds to form and rain to concentrate in a shorter space of time, being able to discharge between 100 and 200 liters per square meter in just one hour. According to climate change projections for the coming decades, the temperature of the Mediterranean will continue to rise. This has already risen 0.8ºC in the last hundred years on the Spanish Mediterranean coast and with an accelerated rise since 1980.
