This post is a comment on the meteorological aspect of the heavy rains last week in Spain. It begins with a quote from an earlier post, followed by comments to a video in Spanish and excerpts from various Wikis. Then I tried to find some data that could illustrate what happened. At the end, I make a few comments about what people think of the event and add my current perspective.
Yesterday at 11:53 PM I posted from an article:
What is DANA weather in Spain
Updated June 2024
DANA is a Spanish acronym for
Depresión Aislada en Niveles Altos. It translates to"
Isolated Depression at High Altitudes". A DANA is a type of weather phenomenon in which
a "pocket" of cold air in the upper atmosphere separates from the main stream and sweeps over a warmer air mass. This process can result in severe weather, including heavy rains, and flooding. In recent years there has been an increase in heavy and torrential rains on the Mediterranean side of the Iberian peninsula.
During a DANA alert, stay indoors is possible and if you are driving, be aware of flooding and strong water currents, especially in hilly and mountainous areas where mudslides area risk.
"La gota fría" is another Spanish expression often heard in connection with the DANA weather system. "La gota fría" literally means "the cold drop". This term refers to the same phenomenon as a DANA when a "pocket" or "drop" of cold air forms in the upper atmosphere and separates from the main stream.
"La gota fría" is a well-known expression in Spain, especially in the coastal regions where this phenomenon is common and can cause severe storms.
However, I did not think I understood it well enough, so I looked for more explanations: I found a video in Spanish from BBC:
Qué es una DANA, el fenómeno meteorológico que provocó el peor desastre natural del siglo en España whch translated is "What is a DANA, the meteorological phenomenon that caused the worst natural disaster of the century in Spain"
The person is saying, from what I understand, that Jet Stream air circulating at an altitude of 11,000 meters, introduced cold air coming from Greenland over Spain which collided with humid warm air over the Mediterranean. (Warmer air can hold much more water vapor than colder air. When warm humid air is then suddenly cooled down, the water vapor condenses.)
The video has this text below:
Climate change
United Nations • Climate change refers to long-term shifts in temperatures and weather patterns. Human activities have been the main driver of climate change, primarily due to the burning of fossil fuels like coal, oil and gas.
Comment: Some in the global media landscape use every possible opportunity to push for the anthropogenic climate change narrative and the presented or implied solution of the green agenda. Burn less coal, oil, and gas and heaven will be restored.
Then I went to the Wikis. This can be both good and bad, but it still helped to make the concepts clearer after looking up a few entries:
The
English Wiki for "Cold drop" has:
A
cold drop is a term used in Spain and France that has commonly come to refer to any high impact rainfall events occurring in the autumn along the Spanish Mediterranean coast or across France.
In Europe, cold drops belong to the characteristics of the Mediterranean climate.
The Spanish-language name of gota fría was directly adapted from the term Kaltlufttropfen introduced by German meteorologists, and became very popular in 1980s Spain as a
blanket term to refer to any high-impact rainfall event.
In the Spanish Levante, these events are typically caused by the interaction of upper-level low pressure systems strangled and ultimately detached from the zonal (eastward) circulation displaying stationary or retrograde (westward) circulation with humid and warmer air masses provided by an overheated Mediterranean in the Autumn. The Spanish equivalent of
cut-off low is DANA (
Depresión Aislada en Niveles Altos). Such recurring synoptic configurations are not necessarily associated to cold drop events.
[...]
Spain
If a sudden cut off in the jet stream takes place (particularly on the
Atlantic Ocean),
a pocket of cold air detaches from the main jet stream, penetrating to the south over the Pyrenees into the warm air in Spain, causing its most dramatic effects in the Southeast of Spain, particularly along the Spanish
Mediterranean coast, especially in the
Valencian Community. The torrential rain caused by a cold drop can result in devastation caused by torrents and
flash floods.
This phenomenon is associated with extremely violent downpours and storms, but not always accompanied by significant rainfall.
For this, high atmospheric instability in the lower air layers needs to combine with a significant amount of moisture.
Disasters
The great Valencia flood on 14 October 1957 was the result of a three-day-long cold drop and caused the deaths of at least 81 people.
The
Vallès floods on 25 September 1962 in the province of Barcelona were caused by a cold drop (gota fría), heavy rain, overflowing the Llobregat and Besòs rivers. The official death toll was 617.
On the night of 29-30 October 2024,
a DANA caused considerable loss of life and extensive damage, especially in the
Valencian Community and the provinces of Albacete, Almería, and Málaga.
Other areas
Cut-off lows are apparent near the
Sierra Nevada de Santa Marta in the
Colombian Caribbean, with peaks surpassing 5 km in altitude in close proximity to a warm sea.
They can also occur elsewhere in the southern hemisphere, such as in South Africa, Namibia, South America and southern Australia. In the northern hemisphere, besides Southern Europe and France, they can occur in China and Siberia, North Pacific, Northeastern United States and the northeast Atlantic.
The
German Wiki "Kaltlufttropfen" explains if translated:
Meteorologists refer to a high-altitude low in the upper troposphere as a cold air drop. It is created through a cut-off process.
Construction[edit] Edit source]
It consists of very cold air of polar origin, typically has a horizontal extension of 300 to 1000 km and is located at an altitude of 5,000 to 10,000 meters above sea level. A drop of cold air is not recognizable as a low-pressure area on the ground; at most, it is noticeable by a small cyclonic bulge of the isobars. A drop of cold air also has no fronts. However, during its passage about the same weather phenomena can be observed as with a low, only in reverse order:
Front: Especially in winter cloud formations with showers like in a cold front, otherwise due to sinking processes cloudiness decrease or clearing clouds.
Back: Area of closed sliding clouds with sometimes longer-lasting precipitation as in a warm front – not as pronounced in summer.
Center: Low altitude temperatures cause high instability, therefore often high-reaching cumulus clouds with showers and thunderstorms, especially in summer. The weather situation that led to the so-called Heinrichsflut in northern Hesse, eastern Westphalia and southern Lower Saxony in July 1965 is considered an example of such a severe thunderstorm situation.
A barometer on the ground can indicate high pressure despite the presence of a drop of cold air and thus suggest 'fine weather'. However, it is usually very cloudy and the long-lived eddies that form at altitude can cause violent thunderstorms and snowfall in winter.
Gota Fría[edit] Edit source]
In Spain, cold drop repeatedly cause intense precipitation and storms, especially in autumn. If the surface temperature of the Mediterranean Sea is still relatively high and there is a high-altitude low south of Spain, a lot of rising moisture can be transported over the Spanish mainland by the counterclockwise rotating air masses. When several factors interact (air pressure at lower altitudes, jet streams, orography, etc.), storms occur, which are called Gota Fría (literally: 'cold drop') after the Spanish translation for cold air drop. Since the 1980s, Gota Fría has been increasingly used as a name for any type of heavy rainfall, Spanish meteorologists have started to refer to cold drop as depresión aislada en niveles altos (DANA, German: 'isolated high-altitude low'). [1]
The DANA phenomenon is mainly associated with the Spanish mainland and the Mediterranean Sea, but it is not limited to these regions. It can actually occur in the Atlantic Ocean as well, including the Canary Islands. These have a year-round mild climate with relatively warm sea temperatures, which contributes to the formation of rising moist air masses. If an isolated high-altitude low forms and passes over these warm and humid air masses, this can lead to strong storms and intense precipitation, similar to the Spanish mainland. [2]
A Gota Fría, for example, led to the Great Flood of Valencia in 1957 and the flood disaster in Spain in 2024 with more than 200 deaths.
The English Wiki has a note that suggests merging the "Cold drop" Wiki with the "Cut-off low" which explains:
A
cut-off low (or
cutoff low), sometimes referred to as the
weatherman's woe, is defined by the National Weather Service as
"a closed upper-level low which has become completely displaced (cut off) from basic westerly current, and moves independently of that current." Cut-off lows form in mid-latitudes (usually in the subtropics or between 20° and 45°) and can remain nearly stationary for days.
Formation
A cut-off low is a cold-core low where wind in the upper levels of the troposphere is "cut off" from the primary westerly winds of the jet stream. They are formed when a trough in the upper-air flow pinches off and separates into a closed circulation. It is defined by concentric isotherms around the core of the low.
Because they are a feature of the mid- to upper-troposphere, they may not be visible on a surface weather analysis. Because they are separated from the main westerly flow, cut-off lows can move slowly and erratically. In certain arrangements, known as a
block or a blocking pattern, they can remain in place for long periods of time.
Whilst cut-off lows can form at any time of the year,
they are more common in autumn, winter and spring in much of the areas affected, particularly in Australia and the Mediterranean Basin, when a mass of polar air is brought towards more southern regions (or northern, in the southern hemisphere) by the jet stream moving between 5 and 9 km
altitude.
[...]
Characteristics
A cut-off low situated over Italy and the tip of northern Libya.
The diameter of a cut-off low can vary from a few hundred to a thousand kilometers. The air there is homogeneous and without a front line separating it from the surrounding masses, while having a decisive influence on the weather. It then most often leads to an atmospheric blocking circulation and the formation of an upper level low. High cold drops, between 1,000 and 10,000 m, are regions of low stability, while low cold drops are regions of relatively stable air.
Composed of very cold air of polar origin, it typically has a horizontal extent of 300 to 1000 km and is 5,000 to 10,000 meters above sea level.
Movement
A cut-off low has a slow movement, typically over a confined region, where it produces heavy rainfall. They are volatile,
baroclinic systems that meander to the west with strong
convergence and an ascending motion, especially when they are deepening. A cut-off low can persist from a few days to more than a week. It may be absorbed into the general circulation while another forms in the same place a few days later. The evolution and movement of a cold low, like any weather blockage, is therefore uncertain.
Effects
Effects of a cut-off low of September 1997 in Alicante.
Cut off lows typically create unsettled weather and, in the warm season, they may produce a lot of
thunderstorms. A cut-off low has a slow movement, typically over a confined region, where it produces heavy rainfall, and can result in severe flooding. For example, a cut-off low was responsible for the
July 2021 floods in Europe.
Regional impacts
In southeastern Australia, cut-off lows can be associated with
Australian east coast lows, which are
subtropical cyclones or
extratropical cyclones that originate from the east. In eastern Australia, a cut-off low can bring accumulating and widespread snowfall at low-level areas and as well as elevated regions in the
subtropics.
In Spain, cut-off lows are often referred to as DANA (Depresión Aislada en Niveles Altos, 'Isolated Upper-Level Depression'), which stresses the characteristic of upper-level lows, differentiating them from other lows, such as
thermal lows originating in lower atmosphere levels during the Summer months.
Ventusky has a function that allows for searching the history, and I tried October 29. Here is a screenshot:
The air is coming from the ocean and it is probably humid. The dark colors indicate the amount of precipitation for the three-hour period. The temperature was 21 degrees. The humidity out at sea away from the area of rain was 90 %.
Then changing the parameters, here is a view of the airflow at an altitude of 5500 meters as well as an indication of the temperatures:
Near Valencia, the temperature at 5500 meters was -15 Celsius, while it near the low just south of Spain was minus 22 Celsius. Notice that the high-pressure system over the Atlantic brings cold air from the north to the south.
The Low then spins some of it around presumably causing the clash between cold and warm humid air from the Mediterranean.
Why are the temperatures in the low-pressure system so low compared to the surrounding air masses? I tried to scroll back in the records and found this picture for October 24. This was five days before the downpour. Notice that there is a tongue of cold air from the north, located southwest of Ireland. It has arrived there from higher latitudes and has been spun around by the high-pressure system over the Atlantic.
For October 25 the indications are that something is changing, the cold air from the north has separated and has begun to spin around itself in an independent low-pressure system.
On October 26, the situation is developing, the low is moving south.
October 27, two days before deluge day, shows a clear separation of the low that keeps moving south with the cold air from the north still spinning around itself. In the center of the low, it is minus 26 Celsius.
The day before the deluge, the temperature in the coldest areas of the low at 5500 meters is still minus 25 C.
There is still much I don't understand about the situation. Is it for instance possible that when the warm air coming from the sea hits land and is pushed up, is cooled down faster if there is already colder than usual air at altitude? Here is a geophysical map of the Iberian Peninsula:
While there have been speculations that the rains were assisted, it is difficult to prove they were. There seem to be reasonable explanations for what happened. However, since the governments of many countries have taught their populations to trust them, come plague, hell-fire, or high water, when something does show up where they don't know what to do, or are just plain incompetent, some try to cover their positions, when they know it is so bad that they could be fired or lose the confidence of the populations. Is that why the authorities in Spain, as reported in Spanish media, have had difficulties with counting the dead and the missing?
Agendas do differ, also in governments. Some want to keep their job at all costs. Many, hopefully, sincerely want to help their constituencies and the people they serve, but some may also allow a situation to develop in a certain way and allow others to cover their backsides, because the chaos of the mix of inability, negligence, incompetence, and contradicting rules and regulations not geared to such events, suits what they would like to achieve anyway. As the BBC video, (or was it really Google?) lost no pace to point out:
Climate change
United Nations • Climate change refers to long-term shifts in temperatures and weather patterns. Human activities have been the main driver of climate change, primarily due to the burning of fossil fuels like coal, oil and gas.
While many people in the Valencia area will have to struggle to get back on their feet, one message pressed on the global public seems to be that they need to go green, but also keep their minds shut, and their eyes closed to what is going on around them.
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