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Thermal Effect Of Land Cover And Snow Cover On The Underlying Middle-Thick Seasonal Frozen Ground In The Active Layer In The Changbai Mountains

Posted on:2015-02-14Degree:DoctorType:Dissertation
Country:ChinaCandidate:X J MengFull Text:PDF
GTID:1220330431981722Subject:Physical geography
Abstract/Summary:PDF Full Text Request
Frozen ground is one of the major components in the cryosphere on earth. Itsoccurence, distribution and thermal regime are affected by many factors, especiallyvegetation and snow cover in local scale.In the Changbai Mountains,Northeast China,ground surfaces are generally characterized by extensive presence of land cover andsnow cover,which significantly affect the temperatures of underlying seasonal frozenground,and thus the freeze-thaw processes and formation and evolution of ChangbaiMountains middle-thick seasonal frozen ground.In order to study the thermal effects of land cover and snow cover on groundtemperature in the active layer and at shallow depths,six representative sites werechosen. They include a Korean pine oak forest; a farmland, a wetland in the Mudanling of the Changbai Mountains.In order to understand the thermal impacts of vegetation removal on theunderlying frozen ground, six HOBO machines and three automatic weather stationsand multiple handheld weather instruments were laid in forest,farmland and weland,they were observed two winters.The main conclusions are as follows:1) Different levels of vegetation,the impact on the climate are not the same. Sinceplants up,canopy dense and multi-layer film, the forest has a strong cooling effect inwinter. Analysis shows that,the canopy will absorb and reflect about40%of the solarradition compared with the top of canopy, thus leading to the low temperatures,thecooling rate is about2℃. Due to the larger spacing,plant height and leaves litter in thewinter,its impact on the solar radiationg is very small,so little effect on theunderlying soil ground temperature.Wetland vegetations height is small,the coolingeffect is not large,but slightly higher than the arable land.2)Due to different individuals and coverage of the morphology, differenttemperature on the underlying soil. Monitoring found forest cooling effect can beobvious,shallow geothermal temperature can displaced about2℃, ahead of frozentime and increased frozen depth.The arable and grassland are relatively weak.3)The influence of snow to the seasonal frozen ground during thaw and melttimes are different.Snow has strong insulation effect,different depths in differentinsulation influence.In the area of Changbai Mountains, less than5cm of snow underlying shallow geothermal has little influence, but the snow in the15-20cm, thedisplacement caused by the temperature at about2-4.1℃, scholars often draw if theplot Xiaoli snow depths exceeding80cm, can cause more than7.79℃temperatureshift. Snow early in the soil freezing, shallow geothermal weakening performance isreduced, so that the freezing depth shallow, but in the soil thawed, because it needs toabsorb a lot of latent heat, resulting in a slower recovery in the shallow groundtemperature, soil freezing time was prolonged.4)Disturbance of vegetation and snow cover have a great impact on theseasonally frozen. Clear vegetation, so that the surface is completely bare, thenremoved the cooling effect of vegetation, so that the time delay of the underlying soilfreezing, freezing depth changes. Different snow cover have an impact on the responseto the underlying soil temperature. However, there is often a cross between the twoaffected after that vegetation cleared, uncleared snow plots compared to thickerplots,the insulation effect is manifested.5)Through active and passive Remote sensing of snow and ground, we get lots ofmaps of Changbai Mountains during2001to2010.These maps will be placed on theland use map, According to interfere with the ability of vegetation and snow surfacetemperature, we adjusted the data on the grid. Then look foe isotherm10.2℃as thesouthern boundary of middle-thick seasonal frozen ground. Its movements arediscussed. Its show that the line moves a lot.In fact, the study on the influences of vegetation and snow on groundtemperatures and freeze-thaw process in the Changbai Mountains, Northeastern Chinais still at the initial stage. The results of this paper just lay the foundation for laterstudies and long-term monitoring.
Keywords/Search Tags:Changbai Mountain, Forests, Snow cover, Seasonal Frozen Soil, Thermal regimes
PDF Full Text Request
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