Surely you have ever heard someone mention the term cold drop or DANA (Isolated Depression at High Levels), especially if you live in Spain or are aware of the news there. This atmospheric phenomenon causes instability in the climate and a drop in temperatures, but what does “the cold drop” mean?
In this AgroCorrn article we are going to talk about what cold drop is , its main characteristics, how it is formed and its effects that can be devastating.
What is cold drop – definition
According to the State Meteorological Agency, a cold drop or DANA (High Level Insulated Depression) is a large mass of air at low temperature that has separated from a polar jet. This, being in areas with a warmer climate , interacts with the higher temperature air in the area and causes storms of all kinds and meteorological instability, which can cause, among other things, winds of up to 100 km / h.
It is more common for them to occur in coastal areas next to warm waters, since the moisture-laden air that rises from these warm seas favors the formation of these cold drops when it meets the polar jets. This is the case of, for example, the Mediterranean coast. Furthermore, DANAs can have quite large diameters, up to several hundred kilometers.
How the cold drop is formed
To talk about the formation of the cold drop, the concept of the polar jet must first be explained . This is a very cold air current that occurs around one of the two poles of the planet. It is a stream with great force and little thickness, hence its name jet, which can travel at more than 180 km / h. They occur at an altitude of between 7 and 12 km above sea level and their shape tends to meander depending on the specific climatic conditions.
When one of these polar jets comes into contact with the warm winds from areas such as the Mediterranean, sometimes a part of that jet “breaks” or separates from the original current. When this happens, that cold air mass is trapped between warmer currents, giving itself the so-called cold drop or DANA .
Of course, this does not always happen, and certain atmospheric circumstances are necessary for a part of that polar jet to separate. It is more common for these circumstances to occur, for example, in summer, since the horizontal thermal gradient is smaller and it is easier for the polar jet to give rise to more turns and meanders in its path, which makes it easier for one of them to be able to end up closing and isolating itself. For example, on the Mediterranean coast, the vast majority of these phenomena occur between September and November.
Effects of cold drop
DANA does not have a fixed duration and its effects last until the cold air mixes with the surrounding warm air and dissolves, or until the cold air pocket rejoins the polar jet from which it was separated.
The effects of the cold drop or DANA include torrential rains that can cause the overflow of rivers and waterways, electrical storms and high-speed winds and force, which on the coasts can be accompanied by dangerous waves.
Given the effects of a cold drop, a whole package of measures is recommended to take if you are in an area with a cold drop :
- In the face of torrential rains, it is necessary to get away from any watercourse, especially if it is near low areas. It is also necessary to slow down when driving and avoid crossing flooded areas at all costs, since there is no way to know the true depth of the water or its strength until it is too late to avoid it.
- Against storms, it is better to stay inside the car or near buildings and if you are in the open, then you have to avoid trees and metal constructions, such as wire fences, which can conduct lightning electricity at a great distance .
- Faced with strong winds, you should always move away from the coast, reinforce the doors and windows and stay away from cornices and balconies on the street, since old or weak constructions can give way.