| A comprehensive fog observation was conducted during the winter of2010at the Jinzhou (plain) and Xuanen (mountain) of Hubei to study macro-and micro-physical structures of fogs in the area. By use the data of FM-100Fog Monitor, tethered balloon system, visibility meter from eight fog events in two areas, summarized the fundamental characteristics of the fog macro-and micro-physics in Western Hubei. Classed two types by the causations of fog formed and found out they have obvious differences. Fogs in Jinzhou are advection-radiation fog and Xuanen are radiation fog.Macro-physics:fogs in two areas are both liquid fog but the top fog temperature in Xuanen is under0℃. Advection-radiation fog in Jinzhou is first appeared in inversion layer near ground. The durations of this type fog in Jinzhou are between11to15hours, except22Dec (5h). The visibility less than50m is sustained8h (except22Dec). The thicknesses of fog in Jinzhou are180-250m and the depth of22Dec is just60m. During the fog formation thickness is usually less than50m. The inversion layer near ground is becoming wick with the cold advection and fog is developed upward. Fog then weakened gradually with temperature rise after sunrise, which reflected the day-variety of advection-radiation fog; The radiation fog in Xuanen is existed an inversion layer above400-600m not near ground. The relative humidity in inversion base is raised quickly than surface. The low cloud is first appeared in the inversion base and developed downward. The high-inversion is formed by special environment in Xuanen. With the high mountain around, space below400-600m is becoming relative closed and the air can easily be moist because of the radiation. The top of inversion base decide the thickness of this type fog. The life of high-inversion fog is less than4h. The fog layer had a near moist adiabatic lapse rate. The main mechanism is radiative cooling and upward soil heat flux, as well as warming effects and moisture losses through dew deposition from turbulent mixing in the stable boundary layer. The wick vapor input and the upper two factors largely determine the likelihood and timing of high-inversion fog formation. There is no heavy fog appeared in high-inversion fog.Micro-physics:The average number concentration of advection-radiation fogs in Jinzhou is equivalent to those in Nanjing of2006, yet the maximum is larger than Nanjing. The average LWC of fogs in Jinzhou is smaller than Nanjing of2006because of short time water vapor transportation. The number concentration and LWC of radiation fogs in Xuanen is smaller than Jinzhou and Nanjing. The maximum of average number concentration and LWC are only34cm-3and0.01g/m3, both are less than the observation of Nailing Mountain. The average droplet spectrums of two stations are similar and both of the number concentration declined exponentially with the increase of droplet diameter and droplets with a smaller diameter dominated, but in the section of droplets with a diameter above30μm the droplet numbers in Xuanen is larger than Jinzhou. One fog in Jinzhou appeared narrow-droplet spectrum and all fog events in Xuanen are broad-droplet spectrum, this is due to radiation fog in Xuanen is formed by low cloud attach the surface.The data of8fog episodes droplet spectrum are analyzed by the Morlet wavelet transformation. It shows that there exist several quasi-periodic oscillations:less than10minutes,10to30minutes,40minutes and100minutes, and also exist180minutes periodic variations of22Dec fog event in Jinzhou. The periodic less than10minutes is mainly occurred in mature period, which is related to fog microphysical process such as fog condensation, collection-sedimentation-condensation and collection. The long periodic is mainly due to advection. But large than100minutes periodic is not understand well, maybe because of the smoothing effect by instrument or the terrain, it needs further study. |
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