Weather conditions conducive to the formation of mountain valley wind

The weather condition favorable to the formation of mountain valley wind is the large temperature difference between day and night between hillside and plain.

The cause of mountain valley wind is mainly the temperature difference between hillside and valley, mountain and plain when day and night alternate. The temperature difference brings the density and pressure difference of the near-surface atmosphere, and the pressure gradient force pushes the airflow from the high pressure (low temperature) area to the low pressure (high temperature) area. In addition, the movement of downhill wind and mountain wind at night is also affected by gravity and friction.

The circulation pattern of mountain-valley wind is related to topography, so its performance in basins and plateaus will be different from that in the usual theory, and circulation coupling will occur when it appears simultaneously with other local winds such as urban heat island circulation and land-sea wind. Mountain valley wind is related to agricultural production and urban pollution in mountainous areas, but it usually only dominates the local wind and temperature field changes in sunny days.

The influence of mountain breeze on air quality;

Under static meteorological conditions, the mountain-valley wind has obvious transport and aggregation effects on the discharged air pollutants. In addition to pollution emissions, on windy days, pollutants are blown away by mountain winds (north winds) in the morning and morning. From the afternoon to the first half of the night, the pollutants re-gathered due to the influence of the valley wind (south wind). Air pollutants continue to circulate and accumulate day after day, until the strong cold air goes south and the strong wind completely removes the pollutants, and the pollution process ends.

Sometimes, pollutants keep accumulating and air quality does not change periodically. It may be because it is controlled by a certain weather system, so that its dominant wind direction offsets the valley wind, or it may be because of other meteorological factors, and the valley wind is not obvious. So we can't generalize, but also analyze specific problems.