Climatic conditions of Mount Everest

The climate knowledge of Mount Everest mainly includes the start and end time of rainy season, the change of high-altitude wind above 7000 meters and the daily change of surface wind speed at different heights. Understanding the start and end time of the rainy season of Mount Everest is mainly to arrange the climbing plan of Mount Everest, and try to avoid the rainy season and choose the dry season. It is more important for climbing from the north side to understand the change of high-altitude wind above 7000 meters of Mount Everest. According to the experience of mountain climbers in China, the season when the wind speed is less than 6 winds should be chosen to climb Mount Everest. The climate mentioned above is an important meteorological basis for climbers to choose the climbing season of Mount Everest. Understanding the daily variation of surface wind speed in mountainous areas is mainly for the schedule of climbing mountains every day.

This is a special weather phenomenon on the north side of Mount Everest. Generally, the mountain valley wind with obvious daily changes often prevails in mountainous areas. In a day and night, the phenomenon of alternating downhill wind and uphill wind is called valley wind. Generally speaking, mountain wind is also called valley wind, and air flows from the valley to the hillside; Downhill wind is also called mountain wind, and air flows from hillside to valley. The main reason for the formation of mountain valley wind is that the underlying surface in the valley and the atmosphere in the valley receive different solar radiation, resulting in the difference between the temperature on the hillside and the temperature at the same height in the valley. Generally speaking, it's mountain breeze from noon to midnight local time, and it's valley breeze at other times.

On the north side of Mount Qomolangma, the ice and snow surface is mainly at an altitude of 5300-7000m. After sunrise, the ice and snow surface temperature is still lower than the atmospheric temperature at the same height in the valley, so the downhill wind prevails almost day and night. The downhill wind formed by this glacier distribution is also called glacier wind. Glacier winds are strongest at 2-6 pm local time. The average wind speed below the ground 1000m can reach 10m/s, and the gust can reach 7-8.

Generally speaking, the daily variation of river flow in mountainous areas is mainly determined by the daily variation of glacial meltwater, which is mainly determined by the daily variation of temperature. After sunrise in spring, summer and autumn, when the sun shines on the surface of the glacier, the glacier gradually melts, and the running water flows into the valley, increasing the river flow. About 67% of the flow of Rongbu River on Mount Everest comes from glacial meltwater. Therefore, the flow of alpine rivers is very small before noon, and it is the largest in the afternoon to evening.

Seeing the weather from the clouds in mountain areas, there is a certain relationship between clouds and weather changes. Experienced climbers can infer short-term weather changes from the morphological changes of clouds, especially when climbing in northern Zhu Feng. The unique "Yun Qi" change of Mount Everest is closely related to weather changes.

The so-called "Yun Qi" refers to the convective "cumulus clouds" continuously generated at the top of Mount Everest. Affected by high-altitude strong winds, it fluttered with the wind. From a distance, it looks like a special weather phenomenon, with a flag hanging on the top of the mountain.

Observations and studies show that most of the "Yun Qi" at the top of Mount Everest floats from west to east, but when a special weather system comes, the "Yun Qi" will also float from east to west.

We know from many weather forecasts for climbing Mount Qomolangma that "Yun Qi" on the top of Mount Qomolangma can really be called "the highest weather vane in the world".

First of all, the wind direction near the top of Mount Qomolangma (8000-9000m above sea level) can be judged from the floating direction of Mount Qomolangma "Yun Qi". Secondly, the wind speed in the upper air can be estimated from the undulating wave shape at the top of Yun Qi.

If "Yun Qi" floats from west to east, and the cloud top is flat and smooth, after leaving the peak, the height of the cloud top gradually decreases or the cloud top fluctuates violently. The high-altitude westerly wind speed is more than 17 meters per second, which is not suitable for mountaineering activities above 7000 meters on that day.

If "Yun Qi" flutters from southwest to northeast, the cloud top fluctuates greatly, and the height of the cloud top gradually rises after leaving the peak, which means that the wind speed in the upper air does not exceed 15 m/s, and mountaineering activities can be carried out above 7000 m on the same day. But a day later, the high-altitude westerly trough will appear, and the strong wind will be accompanied by snowfall. 2-3 days is not suitable for mountaineering activities above 7000 meters. If "Yun Qi" flutters from east to west, it means that there is an easterly airflow in the upper air, and there will be a low pressure in India in the next 1-3 days, which will bring heavy snow and light winds. Generally speaking, it is not suitable for mountaineering activities above 7000 meters. However, on the north side of Mount Everest, for climbers who are familiar with the terrain and climbing route, they can also use this windy and hot weather to climb below 8500 meters, because the biggest threat to climbers from the north side is strong wind.

If there are few clouds on the top of Mount Everest, no "flag clouds" are formed, and the clouds are almost vertical, it means that the high-altitude wind force is less than 15 m/s, which is suitable for mountaineering activities above 7000 meters. If there are pod-shaped cumulus clouds near the top of Mount Everest, it means that the atmospheric structure near the peak is stable and the high-altitude wind force is not strong, which is also suitable for mountaineering activities above 7400 meters.