5:15 PM - 7:15 PM
[MIS12-P14] Variation and Meteorological Conditions of Cold-Air-Pool Structure in Kamikochi
Keywords:Mountain region, Cold-Air-Pool, Radiation cooling, Temperature inversion, The Northern Japanese Alps
In basin-like terrain surrounded by ridges, cold air generated by radiative cooling tends to accumulate in valley bottoms, causing a phenomenon called Cold-Air-Pool, in which the lower the elevation, the lower the temperature. While there are many examples of intensive, short-term studies of Cold-Air-Pool, there are few examples that mention variations in the structure and characteristics of Cold-Air-Pool based on medium- to long-term observations over multiple years. In this study, seasonal variations in the structure (layer thickness, inversion strength) and characteristics (frequency, duration) of Cold-Air-Pool in the Kamikochi region are discussed based on seven years of observations from December 2016 to November 2023, using pressure patterns and observed values.
The frequency of Cold-Air-Pool formation tended to be low in winter and increased during summer. The layer thickness and inversion strength of the Cold-Air-Pool tended to increase from late autumn to winter and decrease during summer. The duration of the inversion tended to be longest in autumn and shortest in spring. The monthly mean values of the layer thicknessl, inversion strength, and duration were positively correlated with each other, with thicker Cold-Air-Pool tending to have greater inversion strength and longer duration. The specific humidity, the layer thickness, and the inversion strength at the upper elevations were negatively correlated, indicating that seasonal changes in specific humidity also affected seasonal changes in the structure of the Cold-Air-Pool.
In the spring season, the weather changes rapidly, and the time for the formation of Cold-Air-Pool is shortened even when the high pressure system covers the area. Therefore, the formation of thickly layered, well-developed Cold-Air-Pool is difficult. In summer, the frequency of formation increases, but the specific humidity is high and radiative cooling is suppressed, resulting in a thin layer and low inversion intensity. In autumn, high pressure and clear and calm days tend to occur continuously, resulting in the formation of Cold-Air-Pool with thick layers and long durations. In winter, the frequency of anticyclonic coverage is the lowest and the duration is shorter than in autumn, but the specific humidity is the lowest, and Cold-Air-Pool with thicker layers and greater inversion strength are more likely to form.
The frequency of Cold-Air-Pool formation tended to be low in winter and increased during summer. The layer thickness and inversion strength of the Cold-Air-Pool tended to increase from late autumn to winter and decrease during summer. The duration of the inversion tended to be longest in autumn and shortest in spring. The monthly mean values of the layer thicknessl, inversion strength, and duration were positively correlated with each other, with thicker Cold-Air-Pool tending to have greater inversion strength and longer duration. The specific humidity, the layer thickness, and the inversion strength at the upper elevations were negatively correlated, indicating that seasonal changes in specific humidity also affected seasonal changes in the structure of the Cold-Air-Pool.
In the spring season, the weather changes rapidly, and the time for the formation of Cold-Air-Pool is shortened even when the high pressure system covers the area. Therefore, the formation of thickly layered, well-developed Cold-Air-Pool is difficult. In summer, the frequency of formation increases, but the specific humidity is high and radiative cooling is suppressed, resulting in a thin layer and low inversion intensity. In autumn, high pressure and clear and calm days tend to occur continuously, resulting in the formation of Cold-Air-Pool with thick layers and long durations. In winter, the frequency of anticyclonic coverage is the lowest and the duration is shorter than in autumn, but the specific humidity is the lowest, and Cold-Air-Pool with thicker layers and greater inversion strength are more likely to form.