Forest canopy reduces shortwave radiation and increases the incoming longwave radiation to snowpacks beneath forest canopies. Furthermore, the effect of forest canopy may be changed by complex topography. In this pape...Forest canopy reduces shortwave radiation and increases the incoming longwave radiation to snowpacks beneath forest canopies. Furthermore, the effect of forest canopy may be changed by complex topography. In this paper, we measured and simulated the incoming longwave radiation to snow beneath forest at different canopy openness in the west Tianshan Mountains, China(43°16'N, 84°24'E) during spring 2013. A sensitivity study was conducted to explore the way that terrain influenced the incoming longwave radiation to snow beneath forest canopies. In the simulation model, measurement datasets, including air temperature, incoming shortwave radiation above canopy, and longwave radiation enhanced by adjacent terrain, were applied to calculate the incoming longwave radiation to snow beneath forest canopy. The simulation results were consistent with the measurements on hourly scale and daily scale. The effect of longwave radiation enhanced by terrain was important than that of shortwave radiation above forest canopy with different openness except the 20% canopy openness. The longwave radiation enhanced due to adjacent terrain increases with the slope increase and temperature rise. When air temperature(or slope) is relatively low, thelongwave radiation enhanced by adjacent terrain is not sensitive to slope(or air temperature), but the sensitivity increases with the decrease of snow cover area on sunny slope. The effect of longwave radiation is especially sensitive when the snow cover on sunny slope melts completely. The effect of incoming shortwave radiation reflected by adjacent terrain on incoming longwave radiation to snow beneath forest canopies is more slight than that of the enhanced longwave radiation.展开更多
This study used SKS waveforms from the International Deep Profiling of Tibet and the Himalayas(INDEPTH) III dataset and a new 2D method for modeling seismic waves in anisotropic media to construct an image of anisotro...This study used SKS waveforms from the International Deep Profiling of Tibet and the Himalayas(INDEPTH) III dataset and a new 2D method for modeling seismic waves in anisotropic media to construct an image of anisotropic structures beneath central Tibet.A preferred model revealed three-segment anisotropic structures in the upper mantle beneath the study region.Waveform modeling demonstrated that the anisotropy was mainly generated by the lithosphere but not the asthenosphere,and that an anisotropic model with a flatter axis of symmetry provides a more consistent interpretation of the observations than models having steeply dipping symmetry axes.A relatively low velocity zone may underlie or intermingle with the anisotropic structures in the northern portion of the region.Synthetic tests also indicate that variations in the elastic constants and depth extent of the anisotropy assumed by the calculations do not affect the general conclusions,although trade-offs exist among certain model parameters.The modeling results suggest that the complex seismic structures in central Tibet were associated with underthrusting of the Indian lithosphere beneath the Asian lithosphere;the inferred flat symmetry axis of the anisotropy was likely generated during this collision process.If this were not the case,the inherited anisotropy would exhibit a steeply dipping axis of symmetry,parallel to the direction of underthrusting.展开更多
基金funded by National Key Technology Research and Development Program of the Ministry of Science and Technology of China(Grant No.2012BAC23B01)National Natural Science Foundation of China(Grant Nos.41271098,41171066)China Special Fund for Meteorological Research in the Public Interest(GYHY201206026)
文摘Forest canopy reduces shortwave radiation and increases the incoming longwave radiation to snowpacks beneath forest canopies. Furthermore, the effect of forest canopy may be changed by complex topography. In this paper, we measured and simulated the incoming longwave radiation to snow beneath forest at different canopy openness in the west Tianshan Mountains, China(43°16'N, 84°24'E) during spring 2013. A sensitivity study was conducted to explore the way that terrain influenced the incoming longwave radiation to snow beneath forest canopies. In the simulation model, measurement datasets, including air temperature, incoming shortwave radiation above canopy, and longwave radiation enhanced by adjacent terrain, were applied to calculate the incoming longwave radiation to snow beneath forest canopy. The simulation results were consistent with the measurements on hourly scale and daily scale. The effect of longwave radiation enhanced by terrain was important than that of shortwave radiation above forest canopy with different openness except the 20% canopy openness. The longwave radiation enhanced due to adjacent terrain increases with the slope increase and temperature rise. When air temperature(or slope) is relatively low, thelongwave radiation enhanced by adjacent terrain is not sensitive to slope(or air temperature), but the sensitivity increases with the decrease of snow cover area on sunny slope. The effect of longwave radiation is especially sensitive when the snow cover on sunny slope melts completely. The effect of incoming shortwave radiation reflected by adjacent terrain on incoming longwave radiation to snow beneath forest canopies is more slight than that of the enhanced longwave radiation.
基金financially supported by the National Natural Science Foundation of China(Grant No.40974030)
文摘This study used SKS waveforms from the International Deep Profiling of Tibet and the Himalayas(INDEPTH) III dataset and a new 2D method for modeling seismic waves in anisotropic media to construct an image of anisotropic structures beneath central Tibet.A preferred model revealed three-segment anisotropic structures in the upper mantle beneath the study region.Waveform modeling demonstrated that the anisotropy was mainly generated by the lithosphere but not the asthenosphere,and that an anisotropic model with a flatter axis of symmetry provides a more consistent interpretation of the observations than models having steeply dipping symmetry axes.A relatively low velocity zone may underlie or intermingle with the anisotropic structures in the northern portion of the region.Synthetic tests also indicate that variations in the elastic constants and depth extent of the anisotropy assumed by the calculations do not affect the general conclusions,although trade-offs exist among certain model parameters.The modeling results suggest that the complex seismic structures in central Tibet were associated with underthrusting of the Indian lithosphere beneath the Asian lithosphere;the inferred flat symmetry axis of the anisotropy was likely generated during this collision process.If this were not the case,the inherited anisotropy would exhibit a steeply dipping axis of symmetry,parallel to the direction of underthrusting.
