Long narrow ridges of sand lying parallel to the direction of the prevailing winds are called Seif dunes.

Seif dunes are a type of sand dune formation that typically occur in desert regions. They are characterized by their elongated shape and their alignment with the direction of the prevailing wind. Here is a detailed explanation of Seif dunes:

Formation:
Seif dunes are formed by the action of wind on loose sand or sediment. They develop in areas where there is a steady wind blowing predominantly from one direction. The wind picks up sand particles and carries them along, depositing them in elongated ridges. Over time, these ridges grow and evolve into Seif dunes.

Shape and Alignment:
Seif dunes have a characteristic shape that resembles a crescent or a parabolic arc. They have gently sloping windward sides and steeper leeward sides. The windward side is usually smooth and convex, while the leeward side is often steeper and may have a rougher texture. Seif dunes can extend for several kilometers in length and can reach heights of up to 100 meters.

Alignment with Prevailing Winds:
One of the defining features of Seif dunes is their alignment with the direction of the prevailing winds. The prevailing wind blows consistently from one direction, causing the sand particles to accumulate and shape the dunes accordingly. This alignment is a result of the continuous deposition and erosion of sand particles by the wind.

Occurrence:
Seif dunes are commonly found in desert regions, particularly in areas with a dry climate and strong prevailing winds. They can be found in various parts of the world, including the Sahara Desert, Arabian Desert, and the deserts of Australia and North America.

Functions and Importance:
Seif dunes play an important role in desert ecosystems. They provide habitats for a variety of plant and animal species that are adapted to the harsh desert conditions. The dune morphology also affects the local climate by influencing wind patterns and sand movement. Additionally, Seif dunes are of interest to scientists studying desert landscapes and geological processes.

In conclusion, Seif dunes are long narrow ridges of sand that form parallel to the prevailing winds in desert regions. Their unique shape and alignment are a result of the continuous action of wind on loose sand, and they serve important ecological and geomorphological functions in desert ecosystems.