The catabatic or mountain wind

The katabatic wind is a wind that has its origin in the high mountains where the temperatures are quite low. Its etymological origin is the Greek word Catabasis which means descending. That is why another name for this wind is autumn wind. The temperature of the katabatic wind depends on the temperature of the region of origin and the amount of descent. The speed of the winds is generally 5 to 10 knots.

The mountain wind is a cool, high-density, downward wind that flows from the highlands to the stations located at the foot of the hills. As it happens, the rarer atmosphere in the high mountains radiates heat into the atmosphere on a clear, dry night at a much faster rate than on the plains. The slopes of the mountains, under the influence of radiation cooling, cool down much more quickly, and as a consequence, the air in close contact with the slopes of the mountains becomes much cooler. As it cools, it becomes denser and heavier and begins to slide down the slopes of the mountains, under the action of the force of gravity, at a speed normally in the range of 5-10 knots or 9-18 km / h. h. into the deep valley located near or at the foot of the hill plateau location and gets there in the early hours of the morning, causing quite cold there even in the relatively warmer months.

Here we discuss a typical Katabatic wind scenario in Pakistan taking into account the temperatures of Murree Hill Station, Islamabad Mountain Foot Station and Lahore Plain Station.

The Murree Islamabad setting

During the cold and dry fall months, the atmosphere in Murree is usually dry at night. The sky is quite clear and the relative humidity is very low. When the sun sets, due to the clear atmosphere and dry air, the slopes of the Murree Mountains cool at a rapid rate due to the re-radiation of heat accumulated during the day back into the atmosphere. As mountain slopes cool, so does the air in close contact with them. It is now known that temperature is inversely proportional to the density of air. Therefore, the air becomes dense and heavy and under the influence of the force of gravity it begins to descend towards the foot of the hills at an average speed of 5-10 knots. It arrives in Islamabad in the early hours of the morning and creates quite a chill there that would not otherwise be possible if there had not been a catabatic phenomenon. The following temperature comparison will further illustrate the point.

Let’s compare the typical late October temperatures for Murree (a hill station), Islamabad (a plateau station located near the hills), and Lahore (a plain station located away from the hills). As described above, the conditions necessary for a catabatic effect to be fully established are a clear atmosphere, little or no wind at the source location, and low relative humidity. By the way, all of these factors are available in Murree from late October to early November. The temperature in Murree drops sharply at night and the air along the slopes becomes colder, descending towards Islamabad, cooling it more than 5-6 degrees compared to the plain seasons. Sometimes the minimum temperature in Islamabad falls below the Murree minimum, the location of the source of the katabatic wind. Typical nighttime highs and lows for Murree, Islamabad, and Lahore for late October are as follows:

Murree 19 8

Islamabad 29 7

Lahore 31 15

Note the effect of the katabatic wind on the Islamabad low temperature. It is 8 degrees Celsius colder than Lahore, although the maximum is 10 degrees warmer than Murree. Also note the daily temperature range in Islamabad which is a whopping 22 C. This is typical for the Katabatic Regions.

In short, the katabatic wind is a cold, dense wind that drastically alters the temperature regime of the area over which it descends.