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珠海凤凰山陆气相互作用与碳通量观测塔的基本观测及晴天主要观测量的日变化特征

Basic Observations and Diurnal Variation of Key Meteorological Variables on Clear Days in the Phoenix Mountain Area of Zhuhai

  • 摘要: 珠海凤凰山地处北回归线以南,森林植被覆盖率达90%,植被类型为南亚热带常绿阔叶林群落,是岭南地区典型的城市或村庄周边的再生森林,我们选择在凤凰山麓森林冠层较为平缓的低矮坡地建立了陆-气相互作用和碳通量的观测铁塔塔站。本文详细介绍了观测塔的地理环境、初步的仪器布设和基本观测,并利用已获得的资料分析了旱季典型晴天主要观测量的日变化特征。太阳总辐射及其分光辐射和反射辐射的日变化都是比较常规的中午最高的对称结构;冠层接收到的长波辐射比向上长波辐射低;气温日变化的峰值比太阳辐射滞后,白天达到最高值前的气温是低层高于高层,达到最高值后到落日前气温陡然下降,夜晚的气温是低层低于高层。相对湿度凌晨最大,下午最小,夜晚是低层相对偏湿,白天正好相反;11月份,珠海地区盛行旱季的偏北季风,有明显的海陆风的作用,白天的海风较强,夜晚的陆风较弱;森林冠层向大气释放的感热和潜热的量值基本相当,潜热基本为正;感热白天为正,夜晚基本为负;森林冠层吸收的二氧化碳的最高值出现在午后,此时空气中水汽浓度达到最低,向大气释放的二氧化碳在日出后的清晨最大,此时空气中的二氧化碳浓度达到最大,同时空气密度也最大;由于森林冠层高、密度大,土壤湿度基本没有日变化;表层土壤温度日变化的振幅随土壤深度加深而变小,土壤热流的变化是下午高,清晨低。本文还发现了一些值得深入探讨的现象,需要以后根据充沛的资料分析论证。

     

    Abstract: Zhuhai's Phoenix Mountain, where the forest vegetation coverage rate has reached 90%, is located just south of the tropic of cancer.The vegetation type is evergreen broadleaf forest, which represents the typical secondary forest type around cities and villages in Linnan in the south subtropical zone.A tower station for monitoring the interaction and CO2 flux between land and atmosphere has been built in the forest land at the foot of Phoenix Mountain.In this paper, the geographical environment, instruments and basic observations of this tower station are introduced in detail.The diurnal variations of key meteorological variables on a typical clear day in the dry season are analyzed.For total and spectral radiation and their reflection radiation values, results reveal a conventional symmetric structure, with the highest values at noon.Downward longwave radiation is lower than upward longwave radiation for the forest canopy.The peak value of air temperature lags that of solar radiation.The air temperature is lower in the upper layer than in the lower layer before its maximum;and then, after decreasing precipitously from this maximum to sunset during the day, it is lower in the lower layer than in the upper layer at night.For relative humidity, the maximum occurs in the early hours of the morning and the minimum occurs in the afternoon.The air is relatively wet in the lower layer at night, and vice versa during the day.In November, Zhuhai experiences a mainly northerly-blowing monsoon.The land and sea breezes play an obvious role, with the sea breeze being strong and the land breeze weak.The sensible heat fluxes are similar to the latent heat fluxes over the forest canopy, with the latter being basically positive.The sensible heat fluxes are positive during the day and negative at night.The maximum CO2 uptake by the forest canopy occurs in the afternoon, when the water vapor concentration is smallest.The maximum CO2 emission by the forest canopy occurs in the morning, after sunrise, when the CO2 concentration and air density are largest.The soil moisture content is almost constant in the same layer under tall and dense forest.The amplitudes of surface soil temperatures become smaller with soil depth.The soil heat flux is stronger in the afternoon and weaker in the morning.Some of the phenomena revealed in this paper should be analyzed and verified in future work as the datasets of these variables grow.

     

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