Observations and modeling of incoming longwave radiation to snow beneath forest canopies in the west Tianshan Mountains, China

2014 ◽  
Vol 11 (5) ◽  
pp. 1138-1153 ◽  
Author(s):  
Heng Lu ◽  
Wen-shou Wei ◽  
Ming-zhe Liu ◽  
Xi Han ◽  
Wen Hong
Keyword(s):  
Longwave Radiation ◽  
Tianshan Mountains ◽  
The West ◽  
Forest Canopies

scholarly journals Modelling longwave radiation to snow beneath forest canopies using hemispherical photography or linear regression

2008 ◽  
Vol 22 (15) ◽  
pp. 2788-2800 ◽  
Author(s):  
Richard Essery ◽  
John Pomeroy ◽  
Chad Ellis ◽  
Tim Link
Keyword(s):  
Linear Regression ◽  
Longwave Radiation ◽  
Hemispherical Photography ◽  
Forest Canopies

scholarly journals Characteristics of the lower ablation zone of the West Greenland ice sheet for energy-balance modelling

1996 ◽  
Vol 23 ◽  
pp. 160-166 ◽  
Author(s):  
Michiel van den Broeke
Keyword(s):  
Heat Flux ◽  
Energy Balance ◽  
Global Radiation ◽  
Ice Sheet ◽  
Greenland Ice Sheet ◽  
Longwave Radiation ◽  
Turbulent Fluxes ◽  
Ablation Zone ◽  
The West ◽  
West Greenland

In this paper, we present the summer-time energy balance for a site in the lower ablation zone of the West Greenland ice sheet. The summer climate of this part of Greenland is sunny and dry. The energy that is available for melting (on average 174 W m−2or 4.5 cm w.e.d−1) is mainly provided by net global radiation two-thirds and sensible-heat flux (one-third). The contribution of the sub-surface heat flux, the latent-heat flux and the net longwave radiation to the energy balance are small. We tested some parameterizations to calculate energy-balance components that are currently used in general circulation models, energy-balance models and mesoscale meteorological models. For the area and time period under consideration, parameterizations that use screen-level temperature for the calculation of incoming longwave radiation systematically underestimate this quantity by 10 W m−2owing to the proximity of the melting-ice surface that restricts temperature increase of the lowest air layers. The incoming global radiation was predicted correctly. Simple explicit schemes that calculate the stability corrections for turbulent fluxes as a function of the bulk Richardson number tend to underestimate the turbulent fluxes by 15 W m−2. The aerodynamic roughness lengthz0derived from wind-speed profiles appears to be erroneously small, leading to underestimation of the fluxes by 30 W m−2. Probably, the wind profile is distorted by the rough terrain. An estimate ofz0biased on microtopographical survey yielded a more realistic result. Because all errors work in the same direction, the use of some of the parameterizations can cause serious underestimation of the melting energy.

Canopy openness and leaf area in chronosequences of coastal temperate rainforests

2000 ◽  
Vol 30 (2) ◽  
pp. 239-256 ◽  
Author(s):  
Gordon W Frazer ◽  
J A Trofymow ◽  
Kenneth P Lertzman
Keyword(s):  
Leaf Area ◽  
Tsuga Heterophylla ◽  
Thuja Plicata ◽  
Canopy Openness ◽  
East Side ◽  
The West ◽  
Old Growth ◽  
Regional Patterns ◽  
Forest Canopies ◽  
Old Growth Forest

We examined spatial and temporal differences in canopy openness and effective leaf area (Le) in a series of eight forest chronosequences located on southern Vancouver Island, British Columbia. Structural attributes were measured on the west and east side of the island in immature, mature, and old-growth stands using hemispherical photography and the LAI-2000 plant canopy analyzer (PCA). Old-growth forest canopies were distinct from those of younger stands: they were more open, more heterogeneous in their openness, and maintained a lower stand Le. Although the overall developmental trajectories of forests were similar across the study sites, site-to-site differences in the rate and magnitude of these temporal changes indicated that site-specific factors also play a significant role in determining the character of forest canopies and their development. The most significant changes in canopy structure did not emerge until the later stages of stand development (150-200 years). Douglas-fir (Pseudotsuga menziesii (Mirb.) Franco) dominated east-side forests were, on average, more open, more heterogeneous, and had a lower stand Le than the stands dominated by western hemlock (Tsuga heterophylla (Raf.) Sarg.) and western redcedar (Thuja plicata Donn.) forming the west-side chronosequences. Shoot clumping, along with other evidence, suggested that species-related differences in leaf display and the geometry of branching structure might have contributed significantly to these regional patterns.

scholarly journals Investigating Variability of Outgoing Longwave Radiation over Peninsular Malaysia Using Wavelet Transform

2013 ◽  
Vol 26 (10) ◽  
pp. 3415-3428 ◽  
Author(s):  
E. S. Lim ◽  
Uma Das ◽  
C. J. Pan ◽  
K. Abdullah ◽  
C. J. Wong
Keyword(s):  
Wavelet Transform ◽  
West Coast ◽  
Outgoing Longwave Radiation ◽  
Longwave Radiation ◽  
Peninsular Malaysia ◽  
Mountain Range ◽  
Northeast Monsoon ◽  
The West ◽  
Time Frequency ◽  
Semiannual Variation

Abstract The present study analyzes and quantifies the spatial–temporal variability of outgoing longwave radiation (OLR) over peninsular Malaysia using the continuous wavelet transform (CWT) from 2003 to 2010. The goal is to understand the long-term variability of OLR over Malaysia in terms of time–frequency variations in relation to the monsoon period and other weather phenomena. The study regions selected were the west coast, east coast, and southern part of peninsular Malaysia. The OLR variation characteristics in time and space derived from wavelet transform were found to be distinctly different in these three regions. In these three regions, OLR showed significant periodicities dominated by the annual cycle, followed by a semiannual cycle. The west coast of peninsular Malaysia has a lower annual component compared to the other regions because of the rain-sheltering effect by the mountain range that blocked the heavy rainfall from northeast monsoon winds. Besides that, the results show that the wet and dry spells coincide with local monsoon and intermonsoon periods. Meanwhile, the results also revealed that the semiannual variation is statistically significant during 2004–06. The strong semiannual variation is coincident with several droughts that resulted from the strong El Niño events in 2004–06. In addition, the phase plot of wavelet coefficients shows that the variations at various scales are in phase, which coincided with the sudden variations of OLR, indicating heavy flood occurrences in the southern part of peninsular Malaysia. The results show that CWT is a powerful tool for analysis of phenomena involving multiscale interactions that exhibit localization in both time and frequency.

scholarly journals Evaluation and Projection of Wind Speed in the Arid Region of Northwest China Based on CMIP6

2021 ◽  
Vol 13 (20) ◽  
pp. 4076
Author(s):  
Yunxia Long ◽  
Changchun Xu ◽  
Fang Liu ◽  
Yongchang Liu ◽  
Gang Yin
Keyword(s):  
Wind Speed ◽  
Arid Region ◽  
Surface Wind ◽  
Surface Wind Speed ◽  
Northwest China ◽  
Tianshan Mountains ◽  
Model Ensemble ◽  
The West ◽  
The North ◽  
Temporal And Spatial

Near surface wind speed has significant impacts on ecological environment change and climate change. Based on the CN05.1 observation data (a gridded monthly dataset with the resolution of 0.25 latitude by 0.25 longitude over China), this study evaluated the ability of 25 Global Climate Models (GCMs) from Coupled Model Intercomparison Project phase 6 (CMIP6) in simulating the wind speed in the Arid Region of Northwest China (ARNC) during 1971–2014. Then, the temporal and spatial variations in the surface wind speed of ARNC in the 21st century were projected under four Shared Socioeconomic Pathways (SSPs), SSP1-2.6, SSP2-4.5, SSP3-7.0, and SP5-8.5. The results reveal that the preferred-model ensemble (PME) can fairly evaluate the temporal and spatial distribution of surface wind speed with the temporal and spatial correlation coefficients exceeding 0.5 at the significance level of p = 0.05 when compared to the 25 single models and their ensemble mean. After deviation correction, the PME can reproduce the distribution characteristics of high wind speed in the east and low in the west, high in mountainous areas, and low in basins. Unfortunately, no models or model ensemble can accurately reproduce the decreasing magnitude of observed wind speed. In the 21st century, the surface wind speed in the ARNC is projected to increase under SSP1-2.6 scenario but will decrease remarkably under the other three scenarios. Moreover, the higher the emission scenarios, the more significant the surface wind speed decreases. Spatially, the wind speed will increase significantly in the west and southeast of Xinjiang, decrease in the north of Xinjiang and the south of Tarim Basin. What’s more, under the four scenarios, the surface wind speed will decrease in spring, summer and autumn, especially in summer, and increase in winter. The wind speed will decrease significantly in the north of Tianshan Mountains in summer, decrease significantly in the north of Xinjiang and the southern edge of Tarim Basin in spring and autumn, and increase in fluctuation with high values in Tianshan Mountains in winter.

scholarly journals Simulated single-layer forest canopies delay Northern Hemisphere snowmelt

2019 ◽  
Author(s):  
Markus Todt ◽  
Nick Rutter ◽  
Christopher G. Fletcher ◽  
Leanne M. Wake
Keyword(s):  
Snow Cover ◽  
Boreal Forests ◽  
Single Layer ◽  
Longwave Radiation ◽  
Length Change ◽  
Day Length ◽  
Forest Canopies ◽  
Diurnal Cycles ◽  
Community Land Model ◽  
The Impact

Abstract. Single-layer vegetation schemes have been found to overestimate diurnal cycles in longwave radiation beneath forest canopies. This study derives a correction from forest stand-scale simulations, which reduces diurnal cycles of sub-canopy longwave radiation. Correction factors are subsequently implemented in land-only simulations of the Community Land Model version 4.5 (CLM4.5) in order to assess the impact on snow cover. Nighttime underestimations of sub-canopy longwave radiation outweigh daytime overestimations, which leads to underestimated averages over the snow cover season. As a result, snow temperatures are underestimated and snowmelt is delayed in CLM4.5 across evergreen boreal forests. Increasing insolation and day length change the impact of overestimated diurnal cycles on daily average sub-canopy longwave radiation throughout the snowmelt season. Consequently, delay in snowmelt is more substantial where winters are warm and snowmelt occurs early, which results in a shortened snowmelt duration across boreal forests.

Analysis of a severe precipitation process in Aksu Area under the background of the Central Asian Vortex

2020 ◽  
Author(s):  
Nannan Guo ◽  
Yushu Zhou
Keyword(s):  
Water Vapor ◽  
Large Scale ◽  
Heavy Rain ◽  
Tianshan Mountains ◽  
Precipitation Process ◽  
The South ◽  
The West ◽  
Valley Wind ◽  
Central Asian ◽  
Convergence Line

<p>Central Asian Vortices (CAVs) are deep cyclonic systems that occur in the Central Asian and are identified at the 500 hPa level. CAVs are significantly associated with many convective events in the Xinjiang province. In order to strengthen the understanding of the mesoscale systems development mechanisms in torrential rain under the influence of CAVs, we analyzes the rainstorm process occurred in the Aksu region that is near the west of Tianshan Mountains, during June 17 to 18, 2013 basing on a variety of data. The results show that the precipitation process occurs under the background of the circulation of the two ridges in a trough over the middle and high latitudes, and the CAV provides favorable large-scale dynamic and water vapor conditions for this rainstorm. The convergence line is the important mesoscale system, which is formed by the superposition of the CAV circulation and the flow stream around the special topography of the west Tianshan Mountains. Due to the difference of thermal properties between the mountain and desert, the slope wind drives convergence line to move and the strong convection developed along the convergence line triggers strong precipitation in the Aksu region. The WRF is able to well simulate not only the location and intensity of the heavy rain but also the evolution of wind field. Preliminary analysis combined with observations and simulation data shows that under the blockage of west Tianshan Mountains, the south wind accumulates and convergences near the valley. As a result, a local convergence line is formed. Meanwhile, with the adjustment of the large-scale circulation situation, especially after the CAV moves to the vicinity of the Aksu area, one part of the westward flow that comes from the south of the vortex turns into northwest wind after crossing the west Tianshan Mountains, and the other part turns into the northeast wind after passing through the Yili Valley, these two flow aggravate the northerly airflow and enhance the intensity of convergence, thereby promote the formation of mesoscale convergence lines and strengthen it. The eastward airflow-induced water vapor accumulates in front of the southern foot of the Tianshan Mountains, and strengthens as the convergence line moves towards southeast with the enhancement of the valley wind at night. Accompanied with the convergence uplift, the accumulation of water vapor at the foot of the mountain promotes the release of unstable energy and brings heavy precipitation to the Aksu region.</p>

scholarly journals Simulated single-layer forest canopies delay Northern Hemisphere snowmelt

2019 ◽  
Vol 13 (11) ◽  
pp. 3077-3091 ◽  
Author(s):  
Markus Todt ◽  
Nick Rutter ◽  
Christopher G. Fletcher ◽  
Leanne M. Wake
Keyword(s):  
Snow Cover ◽  
Land Surface ◽  
Single Layer ◽  
Longwave Radiation ◽  
Length Change ◽  
Day Length ◽  
Forest Canopies ◽  
Diurnal Cycles ◽  
Community Land Model ◽  
The Impact

Abstract. Single-layer vegetation schemes in modern land surface models have been found to overestimate diurnal cycles in longwave radiation beneath forest canopies. This study introduces an empirical correction, based on forest-stand-scale simulations, which reduces diurnal cycles of sub-canopy longwave radiation. The correction is subsequently implemented in land-only simulations of the Community Land Model version 4.5 (CLM4.5) in order to assess the impact on snow cover. Nighttime underestimations of sub-canopy longwave radiation outweigh daytime overestimations, which leads to underestimated averages over the snow cover season. As a result, snow temperatures are underestimated and snowmelt is delayed in CLM4.5 across evergreen boreal forests. Comparison with global observations confirms this delay and its reduction by correction of sub-canopy longwave radiation. Increasing insolation and day length change the impact of overestimated diurnal cycles on daily average sub-canopy longwave radiation throughout the snowmelt season. Consequently, delay of snowmelt in land-only simulations is more substantial where snowmelt occurs early.

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