On excitation of a near-surface waveguide by a high-elevation source

1995 ◽  
Vol 38 (9) ◽  
pp. 593-597
Author(s):  
G. M. Strelkov ◽  
N. P. Santalov
Keyword(s):  
High Elevation ◽  
Near Surface ◽  
Surface Waveguide

scholarly journals Large Contribution of Coarse Mode to Aerosol Microphysical and Optical Properties: Evidence from Ground-Based Observations of a Transpacific Dust Outbreak at a High-Elevation North American Site

2017 ◽  
Vol 74 (5) ◽  
pp. 1431-1443 ◽  
Author(s):  
E. Kassianov ◽  
M. Pekour ◽  
C. Flynn ◽  
L. K. Berg ◽  
J. Beranek ◽  
...  
Keyword(s):  
North American ◽  
High Elevation ◽  
Saharan Dust ◽  
Large Contribution ◽  
Near Surface ◽  
Dust Transport ◽  
Aerosol Mass ◽  
Coarse Mode ◽  
Median Diameter ◽  
Transpacific Transport

Abstract This work is motivated by previous studies of transatlantic transport of Saharan dust and the observed quasi-static nature of coarse mode aerosol with a volume median diameter (VMD) of approximately 3.5 μm. The authors examine coarse mode contributions from transpacific transport of dust to North American aerosol properties using a dataset collected at the high-elevation Storm Peak Laboratory (SPL) and the nearby Atmospheric Radiation Measurement (ARM) Mobile Facility. Collected ground-based data are complemented by quasi-global model simulations and satellite and ground-based observations. The authors identify a major dust event associated mostly with a transpacific plume (about 65% of near-surface aerosol mass) in which the coarse mode with moderate (~3 μm) VMD is distinct and contributes substantially to total aerosol volume (up to 70%) and scattering (up to 40%). The results demonstrate that the identified plume at the SPL site has a considerable fraction of supermicron particles (VMD ~3 μm) and, thus, suggest that these particles have a fairly invariant behavior despite transpacific transport. If confirmed in additional studies, this invariant behavior may simplify considerably parameterizations for size-dependent processes associated with dust transport and removal.

scholarly journals Climate variables along a traverse line in Dronning Maud Land, East Antarctica

1999 ◽  
Vol 45 (150) ◽  
pp. 295-302 ◽  
Author(s):  
Michiel R. van den Broeke ◽  
Jan-Gunnar Winther ◽  
Elisabeth Isaksson ◽  
Jean Francis Pinglot ◽  
Lars Karlöf ◽  
...  
Keyword(s):  
Potential Temperature ◽  
Ice Sheet ◽  
High Elevation ◽  
Cold Climate ◽  
East Antarctica ◽  
Katabatic Wind ◽  
Near Surface ◽  
Surface Mass ◽  
Drifting Snow ◽  
Dronning Maud Land

AbstractTemperature, density and accumulation data were obtained from shallow firn cores, drilled during an overland traverse through a previously unknown part of Dronning Maud Land, East Antarctica. The traverse area is characterised by high mountains that obstruct the ice flow, resulting in a sudden transition from the polar plateau to the coastal region. The spatial variations of potential temperature, near-surface firn density and accumulation suggest that katabatic winds are active in this region. Proxy wind data derived from firn-density profiles confirm that annual mean wind speed is strongly related to the magnitude of the surface slope. The high elevation of the ice sheet south of the mountains makes for a dry, cold climate, in which mass loss owing to sublimation is small and erosion of snow by the wind has a potentially large impact on the surface mass balance. A simple katabatic-wind model is used to explain the variations of accumulation along the traverse line in terms of divergence/convergence of the local transport of drifting snow. The resulting wind- and snowdrift patterns are closely connected to the topography of the ice sheet: ridges are especially sensitive to erosion, while ice streams and other depressions act as collectors of drifting snow.

scholarly journals Influence of climate variability on water partitioning and effective energy and mass transfer (EEMT) in a semi-arid critical zone

2015 ◽  
Vol 12 (8) ◽  
pp. 7933-7969 ◽  
Author(s):  
X. Zapata-Rios ◽  
P. D. Brooks ◽  
P. A. Troch ◽  
J. McIntosh ◽  
C. Rasmussen
Keyword(s):  
Climate Variability ◽  
Water Availability ◽  
Snow Water Equivalent ◽  
High Elevation ◽  
Critical Zone ◽  
Effective Energy ◽  
Near Surface ◽  
Basin Scale ◽  
Water Partitioning ◽  
Semi Arid

Abstract. The Critical Zone (CZ) is the heterogeneous, near-surface layer of the planet that regulates life-sustaining resources. Previous research has demonstrated that a quantification of the influxes of effective energy and mass (EEMT) to the CZ can predict its structure and function. In this study, we quantify how climate variability in the last three decades (1984–2012) has affected water availability and the temporal trends in EEMT. This study takes place in the 1200 km2 upper Jemez River Basin in northern New Mexico. The analysis of climate, water availability, and EEMT was based on records from two high elevation SNOTEL stations, PRISM data, catchment scale discharge, and satellite derived net primary productivity (MODIS). Records from the two SNOTEL stations showed clear increasing trends in winter and annual temperatures (+1.0–1.3 °C decade−1; +1.2–1.4 °C decade−1, respectively), decreasing trends in winter and annual precipitation (−41.6–51.4 mm decade−1; −69.8–73.2 mm decade−1, respectively) and maximum Snow Water Equivalent (SWE; −33.1–34.7 mm decade−1). The water partitioning fluxes at the basin scale showed statistically significant decreasing trends in precipitation (−61.7 mm decade−1), discharge (−17.6 mm decade−1) and vaporization (−45.7 mm decade−1). Similarly Q50, an indicator of snowmelt timing, is occurring 4.3 days decade−1 earlier. Results from this study indicated a decreasing trend in water availability, a reduction in forest productivity (4 g C m−2 per 10 mm of reduction in Precipitation) and EEMT (1.2–1.3 MJ m2 decade−1). These changes in EEMT point towards a hotter, drier and less productive ecosystem which may alter critical zone processes in high elevation semi-arid systems.

Structure of the Near-Surface Waveguide Layers Produced by Diffusion of Titanium in Lithium Niobate

1999 ◽  
Vol 590 ◽  
Author(s):  
Y. Avrahami ◽  
E. Zolotoyabko ◽  
W. Sauer ◽  
T. H. Metzger ◽  
J. Peisl
Keyword(s):  
Thin Film ◽  
Lithium Niobate ◽  
Grazing Incidence ◽  
Lattice Parameter ◽  
High Temperature Phase ◽  
Temperature Phase ◽  
Near Surface ◽  
Structural Modifications ◽  
Grazing Incidence Diffraction ◽  
Surface Waveguide

ABSTRACTTitanium-induced structural modifications in thin waveguide layers of lithium niobate have been investigated by grazing incidence diffraction and complementary thin film techniques. The study was focused on the high-temperature phase transformation in this system and its influence on the lattice parameter changes, depending on the annealing time.

scholarly journals Why Do Global Climate Models Struggle to Represent Low-Level Clouds in the West African Summer Monsoon?

2017 ◽  
Vol 30 (5) ◽  
pp. 1665-1687 ◽  
Author(s):  
Lisa Hannak ◽  
Peter Knippertz ◽  
Andreas H. Fink ◽  
Anke Kniffka ◽  
Gregor Pante
Keyword(s):  
Climate Models ◽  
Global Climate ◽  
West African Monsoon ◽  
High Elevation ◽  
West African ◽  
Global Climate Models ◽  
The West ◽  
Near Surface ◽  
Low Level ◽  
The Impact

Abstract Climate models struggle to realistically represent the West African monsoon (WAM), which hinders reliable future projections and the development of adequate adaption measures. Low-level clouds over southern West Africa (5°–10°N, 8°W–8°E) during July–September are an integral part of the WAM through their effect on the surface energy balance and precipitation, but their representation in climate models has received little attention. Here 30 (20) years of output from 18 (8) models participating in phase 5 of the Coupled Model Intercomparison Project (Year of Tropical Convection) are used to identify cloud biases and their causes. Compared to ERA-Interim reanalyses, many models show large biases in low-level cloudiness of both signs and a tendency to too high elevation and too weak diurnal cycles. At the same time, these models tend to have too strong low-level jets, the impact of which is unclear because of concomitant effects on temperature and moisture advection as well as turbulent mixing. Part of the differences between the models and ERA-Interim appear to be related to the different subgrid cloud schemes used. While nighttime tendencies in temperature and humidity are broadly realistic in most models, daytime tendencies show large problems with the vertical transport of heat and moisture. Many models simulate too low near-surface relative humidities, leading to insufficient low cloud cover and abundant solar radiation, and thus a too large diurnal cycle in temperature and relative humidity. In the future, targeted model sensitivity experiments will be needed to test possible feedback mechanisms between low clouds, radiation, boundary layer dynamics, precipitation, and the WAM circulation.

scholarly journals Forcing factors of cloud-to-ground lightning over Iberia: regional-scale assessments

2013 ◽  
Vol 13 (7) ◽  
pp. 1745-1758 ◽  
Author(s):  
J. A. Santos ◽  
M. A. Reis ◽  
F. De Pablo ◽  
L. Rivas-Soriano ◽  
S. M. Leite
Keyword(s):  
Regional Scale ◽  
Convective Available Potential Energy ◽  
High Elevation ◽  
Climatic Conditions ◽  
Late Spring ◽  
Near Surface ◽  
Air Temperatures ◽  
Mediterranean Regions ◽  
Cloud To Ground Lightning ◽  
Current Polarity

Abstract. Cloud-to-ground lightning in a sector covering the Iberian Peninsula, the Balearic Islands and nearby seas (36–44° N, 10° W–5° E) is analysed in the period from 2003 to 2009 (7 yr). Two Iberian lightning detection networks, composed of 18 sensors over Portugal and Spain, are combined for the first time in the present study. The selected characteristics are cloud-to-ground flashes (CGFs), first stroke peak current, polarity and multiplicity (number of strokes in a given flash). This study examines the temporal (on hourly, monthly and seasonal timescales) and spatial variability of CGFs. The influence of five forcing factors on lightning (elevation, lifted index, convective available potential energy and daily minimum and maximum near-surface air temperatures) over the Iberian sector is also assessed. For regional-scale assessments, six subsectors with different climatic conditions were analysed separately. Despite important regional differences, the strongest lightning activity occurs from late spring to early autumn, and mostly in the afternoon. Furthermore, CGFs are mainly located over high-elevation areas in late spring to summer, while they tend to occur over the sea in autumn. The results suggest that (1) orographically forced thunderstorms over mountainous areas, mostly from May to September, (2) tropospheric buoyancy forcing over western-central and northern regions in summer and over the Mediterranean regions in autumn, and (3) near-surface thermal contrasts from October to February largely control the location of lightning in Iberia. There is no evidence of different forcings by polarity. A clear correspondence between summertime precipitation patterns and CGFs is also found.

scholarly journals Mapping Interflow Potential and the Validation of Index-Overlay Weightings by Using Coupled Surface Water and Groundwater Flow Model

Water ◽  
2021 ◽  
Vol 13 (17) ◽  
pp. 2452
Author(s):  
Chuen-Fa Ni ◽  
Quoc-Dung Tran ◽  
I-Hsien Lee ◽  
Minh-Hoang Truong ◽  
Shaohua Marko Hsu
Keyword(s):  
Surface Water ◽  
Water Resource ◽  
Water Resource Management ◽  
River Flow ◽  
High Elevation ◽  
Coastal Zones ◽  
Near Surface ◽  
Practical Applications ◽  
Index Overlay ◽  
Overlay Model

Interflow is an important water source contributing to river flow. It directly influences the near-surface water cycles for water resource management. This study focuses on assessing the interflow potential and quantifying the interflow in the downstream area along the Kaoping River in southern Taiwan. The interflow potential is first determined based on the modified index-overlay model, which employs the analytical hierarchy process (AHP) to calculate the ratings and weightings of the selected factors. The groundwater and surface water flow (GSFLOW) numerical model is then used to link the index-overlay model to quantify the interflow potential for practical applications. This study uses the Monte Carlo simulations to assess the influence of rainfall-induced variations on the interflow uncertainty in the study area. Results show that the high potential interflow zones are located in the high to middle elevation regions along the Kaoping River. Numerical simulations of the GSFLOW model show an interflow variation pattern that is similar to the interflow potential results obtained from the index-overlay model. The average interflow rates are approximately 3.5 × 104 (m3/d) in the high elevation zones and 2.0 × 104 (m3/d) near the coastal zones. The rainfall uncertainty strongly influences interflow rates in the wet seasons, especially the peaks of the storms or heavy rainfall events. Interflow rates are relatively stable in the dry seasons, indicating that interflow is a reliable water resource in the study area.

scholarly journals Changes in the firn structure of the Greenland Ice Sheet caused by recent warming

2015 ◽  
Vol 9 (1) ◽  
pp. 541-565 ◽  
Author(s):  
S. de la Peña ◽  
I. M. Howat ◽  
P. W. Nienow ◽  
M. R. van den Broeke ◽  
E. Mosley-Thompson ◽  
...  
Keyword(s):  
Mass Balance ◽  
Ice Sheet ◽  
Greenland Ice Sheet ◽  
Mass Gain ◽  
High Elevation ◽  
Near Surface ◽  
Surface Mass ◽  
Ice Sheet Mass Balance ◽  
Ice Content ◽  
Percolation Zone

Abstract. Atmospheric warming over the Greenland Ice Sheet during the last two decades has increased the amount of surface meltwater production, resulting in the migration of melt and percolation regimes to higher altitudes and an increase in the amount of solid ice from refrozen meltwater found in the firn above the equilibrium line. Here we present observations of near-surface (0–20 m) firn conditions in western Greenland obtained from campaigns between 1998 and 2014. We find a sharp increase in firn ice content in the form of thick widespread layers in the percolation zone, which decreases the capacity of the firn to store meltwater. The estimated total annual ice content retained in the firn in areas with positive surface mass balance west of the ice divide in Greenland reached a maximum of 74 ± 25 Gt in 2012, compared to the 1958–1999 average of 13 ± 2 Gt, while the percolation zone area more than doubled between 2003 and 2012. Increased melt and column densification resulted in surface lowering averaging −0.80 ± 0.39 m yr−1 between 1800 and 2800 m in the accumulation zone of western Greenland. Since 2007, annual melt and refreezing rates in the percolation zone at elevations below 2100 m surpass the annual snowfall from the previous year, implying that mass gain in the region is now in the form of refrozen meltwater. If current melt trends over high elevation regions continue, subsequent changes in firn structure will have implications for the hydrology of the ice sheet and related abrupt seasonal densification could become increasingly significant for altimetry-derived ice sheet mass balance estimates.

scholarly journals Meltwater percolation, impermeable layer formation and runoff buffering on Devon Ice Cap, Canada

2019 ◽  
Vol 66 (255) ◽  
pp. 61-73
Author(s):  
David W. Ashmore ◽  
Douglas W. F. Mair ◽  
David O. Burgess
Keyword(s):  
Pore Space ◽  
Greenland Ice Sheet ◽  
High Elevation ◽  
Layer Formation ◽  
Near Surface ◽  
Surface Mass ◽  
Ice Cap ◽  
Devon Ice Cap ◽  
Impermeable Layer ◽  
Surface Ice

AbstractThe retention of meltwater in the accumulation area of the Greenland ice sheet and other Arctic ice masses buffers their contribution to sea level change. However, sustained warming also results in impermeable ice layers or ‘ice slabs’ that seal the underlying pore space. Here, we use a 1-D, physically based, high-resolution model to simulate the surface mass balance (SMB), percolation, refreezing, ice layer formation and runoff from across the high-elevation area of Devon Ice Cap, Canada, from 2001 to 2016. We vary the thickness of the ‘impermeable’ ice layer at which underlying firn becomes inaccessible to meltwater. Thick near-surface ice layers are established by an initial deep percolation, the formation of decimetre ice layers and the infilling of interleaving pore space. The cumulative SMB increases by 48% by varying impermeable layer thickness between 0.01 and 5 m. Within this range we identify narrower range (0.25–1 m) that can simulate both the temporal variability in SMB and the observed near-surface density structure. Across this range, cumulative SMB variation is limited to 6% and 45–49% of mass retention takes place within the annually replenished snowpack. Our results indicate cooler summers after intense mid-2000s warming have led to a partial replenishment of pore space.

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