Why in news?
Starting on October 28, intense rains hit southern and eastern Spain, submerging towns, cutting off roads, and impacting millions. Flash floods in Valencia have resulted in at least 64 fatalities.
In some regions, more than a month's worth of rain fell within a day, with Andalusia experiencing four times the usual October rainfall. Between 150 and 200 liters per square meter fell in just two hours, according to Spain’s meteorological agency.
The intense rainfall is attributed to “gota fría” (cold drop) or DANA (isolated high-altitude depression), an annual weather pattern that brings heavy rain.
What’s in today’s article?
- Cumulonimbus clouds
- DANA
- Is DANA or cold drop becoming more intense?
Cumulonimbus clouds
- About
- These are large, towering clouds associated with thunderstorms and severe weather.
- They form from warm, moist air rising rapidly in unstable atmospheric conditions and are characterized by their massive, anvil-shaped tops that can reach heights of up to 12,000 meters (39,000 feet) or more.
- These clouds are composed of water droplets at lower levels and ice crystals at higher altitudes due to the cold temperatures.
- Key Characteristics of Cumulonimbus Clouds
- Vertical Growth: They can extend high into the atmosphere, often reaching the stratosphere.
- Thunderstorm Clouds: They are responsible for intense weather phenomena such as thunderstorms, heavy rain, hail, lightning, and even tornadoes.
- Anvil Shape: Their tops spread out in a flat, anvil-like shape when they hit the upper levels of the atmosphere.
- Dense and Dark: They appear dark on the bottom due to the thickness of water droplets, which block sunlight.
DANA
- About
- DANA is the acronym for “depresión aislada en niveles altos,” or isolated depression at high altitudes.
- The DANA (cold drop) phenomenon occurs when cold air descends over the warm Mediterranean waters, creating atmospheric instability.
- This meeting causes a significant temperature difference between the layers of the atmosphere.
- As a result, warm, moist air rises quickly, forming dense cumulonimbus clouds that release heavy rain.
- How DANAs form
- Role of the Polar Jet Stream
- The polar jet stream—a high-altitude, fast-moving wind current separating polar and tropical air—affects the occurrence of DANA, intensifying rainfall patterns in parts of Spain.
- A fast-moving wind current in the troposphere separates cold polar air from warm tropical air.
- Cold air separation
- A pocket of cold air separates from the polar jet stream and descends over the Mediterranean Sea.
- Atmospheric instability
- The contrast between the cold air and warm air causes the warm air to rise quickly, creating atmospheric instability.
- Cumulonimbus clouds
- The rising warm air becomes saturated with water vapor and forms dense cumulonimbus clouds.
- Occurrence
- DANAs are more likely to occur in autumn and spring when temperature variations are more pronounced. They can also cause large hail storms and tornadoes.
- Affected regions
- The clouds produce heavy rain in parts of Spain, Portugal, Italy, France, and other areas around the Mediterranean Sea.
Is DANA or cold drop becoming more intense?
- Increased Frequency and Intensity of Cold Drops
- Experts note that cold drops have become more frequent and intense in recent years, with their effects spreading to a wider geographical area.
- The Spain’s meteorological agency indicated that heavy rains from cold drops now also impact inland cities like Madrid, where such abundant rainfall was previously uncommon.
- Impact of Climate Change
- This change is partly attributed to soaring global temperatures, which allow warmer air to hold more moisture, leading to more intense rainfall.
- The rise in sea surface temperatures of the Mediterranean Sea has further exacerbated the situation, with record high temperatures recorded in August.
- Experts emphasized that cold drops are formed by the interaction of cold air with increasingly hotter surfaces, contributing to this phenomenon.
