scholarly journals Dome C site testing: long term statistics of integrated optical turbulence parameters at ground level

2012 ◽  
Vol 8 (S288) ◽  
pp. 300-301 ◽  
Author(s):  
E. Aristidi ◽  
A. Agabi ◽  
E. Fossat ◽  
A. Ziad ◽  
L. Abe ◽  
...  
Keyword(s):  
Strong Dependence ◽  
Ground Level ◽  
Bright Star ◽  
Optical Turbulence ◽  
Outer Scale ◽  
Site Testing ◽  
Visible Wavelength ◽  
Integrated Optical ◽  
Turbulence Parameters

AbstractWe present long term site testing statistics based on DIMM and GSM data obtained at Dome C, Antarctica. These data have been collected on the bright star Canopus since the end of 2003. We give values of the integrated turbulence parameters in the visible (wavelength 500 nm). The median value we obtained for the seeing are 1.2 arcsec, 2.0 arcsec and 0.8 arcsec at respective elevations of 8m, 3m and 20m above the ground. The isoplanatic angle median value is 4.0 arcsec and the median outer scale is 7.5m. We found that both the seeing and the isoplanatic angle exhibit a strong dependence with the season (the seeing is larger in winter while the isoplanatic angle is smaller).

scholarly journals Cloud Cover and Aurora Contamination at Dome A in 2017 from KLCAM

2020 ◽  
Author(s):  
Xu Yang ◽  
Zhaohui Shang ◽  
Keliang Hu ◽  
Yi Hu ◽  
Bin Ma ◽  
...  
Keyword(s):  
Cloud Cover ◽  
Emission Lines ◽  
Austral Winter ◽  
Site Testing ◽  
Dome A ◽  
Astronomical Observations ◽  
Auroral Emission ◽  
Long Term Monitoring ◽  
Term Monitoring

Abstract Dome A in Antarctica has many characteristics that make it an excellent site for astronomical observations, from the optical to the terahertz. Quantitative site testing is still needed to confirm the site’s properties. In this paper, we present a statistical analysis of cloud cover and aurora contamination from the Kunlun Cloud and Aurora Monitor (KLCAM). KLCAM is an automatic, unattended all-sky camera aiming for long-term monitoring of the usable observing time and optical sky background at Dome A. It was installed at Dome A in January 2017, worked through the austral winter, and collected over 47,000 images over 490 days. A semi-quantitative visual data analysis of cloud cover and auroral contamination was carried out by five individuals. The analysis shows that the night sky was free of clouds for 83 per cent of the time, which ranks Dome A highly in a comparison with other observatory sites. Although aurorae were detected somewhere on an image for nearly 45 per cent of the time, the chance of a point on the sky being affected by an aurora is small. The strongest auroral emission lines can be filtered out with customized filters.

scholarly journals Simultaneous generalized and low-layer SCIDAR turbulence profiles at san pedro mártir observatory

2019 ◽  
Vol 490 (1) ◽  
pp. 1397-1405 ◽  
Author(s):  
R Avila ◽  
O Valdés-Hernández ◽  
L J Sánchez ◽  
I Cruz-González ◽  
J L Avilés ◽  
...  
Keyword(s):  
High Altitude ◽  
Wind Direction ◽  
Close Agreement ◽  
Baja California ◽  
Ground Level ◽  
Combined Effect ◽  
Moderate Altitude ◽  
San Pedro ◽  
Simultaneous Measurements

ABSTRACT We present optical turbulence profiles obtained with a Generalized SCIDAR (G-SCIDAR) and a low-layer SCIDAR (LOLAS) at the Observatorio Astronómico Nacional in San Pedro Mártir (OAN-SPM), Baja California, Mexico, during three observing campaigns in 2013, 2014, and 2015. The G-SCIDAR delivers profiles with moderate altitude-resolution (a few hundred metres) along the entire turbulent section of the atmosphere, while the LOLAS gives high altitude resolution (on the order of tens of metres) but only within the first few hundred metres. Simultaneous measurements were obtained on 2014 and allowed us to characterize in detail the combined effect of the local orography and wind direction on the turbulence distribution close to the ground. At the beginning of several nights, the LOLAS profiles show that turbulence peaks between 25 and 50 m above the ground, not at ground level as was expected. The G-SCIDAR profiles exhibit a peak within the first kilometre. In 55 per cent and 36 per cent of the nights stable layers are detected between 10 and 15 km and at 3 km, respectively. This distribution is consistent with the results obtained with a G-SCIDAR in 1997 and 2000 observing campaigns. Statistics computed with the 7891 profiles that have been measured at the OAN-SPM with a G-SCIDAR in 1997, 2000, 2014, and 2015 campaigns are presented. The seeing values calculated with each of those profiles have a median of 0.79, first and third quartiles of 0.51 and 1.08 arcsec, which are in close agreement with other long term seeing monitoring performed at the OAN-SPM.

scholarly journals Long-term O<sub>3</sub>–precursor relationships in Hong Kong: field observation and model simulation

2017 ◽  
Vol 17 (18) ◽  
pp. 10919-10935 ◽  
Author(s):  
Yu Wang ◽  
Hao Wang ◽  
Hai Guo ◽  
Xiaopu Lyu ◽  
Hairong Cheng ◽  
...  
Keyword(s):  
Hong Kong ◽  
Model Simulation ◽  
Ground Level ◽  
Effective Control ◽  
Photochemical Pollution ◽  
Mixing Ratios ◽  
The Past ◽  
Total Volatile Organic Compounds

Abstract. Over the past 10 years (2005–2014), ground-level O3 in Hong Kong has consistently increased in all seasons except winter, despite the yearly reduction of its precursors, i.e. nitrogen oxides (NOx =  NO + NO2), total volatile organic compounds (TVOCs), and carbon monoxide (CO). To explain the contradictory phenomena, an observation-based box model (OBM) coupled with CB05 mechanism was applied in order to understand the influence of both locally produced O3 and regional transport. The simulation of locally produced O3 showed an increasing trend in spring, a decreasing trend in autumn, and no changes in summer and winter. The O3 increase in spring was caused by the net effect of more rapid decrease in NO titration and unchanged TVOC reactivity despite decreased TVOC mixing ratios, while the decreased local O3 formation in autumn was mainly due to the reduction of aromatic VOC mixing ratios and the TVOC reactivity and much slower decrease in NO titration. However, the decreased in situ O3 formation in autumn was overridden by the regional contribution, resulting in elevated O3 observations. Furthermore, the OBM-derived relative incremental reactivity indicated that the O3 formation was VOC-limited in all seasons, and that the long-term O3 formation was more sensitive to VOCs and less to NOx and CO in the past 10 years. In addition, the OBM results found that the contributions of aromatics to O3 formation decreased in all seasons of these years, particularly in autumn, probably due to the effective control of solvent-related sources. In contrast, the contributions of alkenes increased, suggesting a continuing need to reduce traffic emissions. The findings provide updated information on photochemical pollution and its impact in Hong Kong.

Composition Dependence of the Judd-Ofelt Intensity Parameters in TeO2-PbF2: Tm3+ Glasses

2004 ◽  
Vol 829 ◽  
Author(s):  
Idris Kabalci ◽  
Gonul Ozen ◽  
Adnan Kurt ◽  
Alphan Sennaroglu
Keyword(s):  
Cross Sections ◽  
Composition Dependence ◽  
Strong Dependence ◽  
Local Environment ◽  
Ground Level ◽  
Absorption Bands ◽  
Intensity Parameters ◽  
Nir Absorption ◽  
Doped Glasses ◽  
Absorption Measurements

ABSTRACTTm3+ -doped glasses with the composition of (1-x)TeO2-xPbF2, where x=10, 15, 20, 25 mol.% were synthesized and, their thermal and absorption measurements were investigated. All the glasses were transparent. The absorption bands corresponding to the absorption of the 1G4, 3F2, 3F3, 3F4, 3H5, and 3H4 levels from the 3H6 ground level of the Tm3+ ion were observed in the optical UV/VIS/NIR absorption measurements. We calculated the integrated absorption cross sections of each band except that of 3H5 level was found to vary with composition of the PbF2. The absorption measurements were first made to determine the spontaneous emission probabilities of the 4f-4f transitions of the Tm3+ ions. The calculations were made by using the Judd - Ofelt theory. The Ω2 parameter shows the strongest dependence on the host composition and it increases with the increasing PbF2 amount. The values Ω4 increases rather slowly while the value of Ω6 is practically independent of the composition. The strong dependence of the parameter Ω2 indicates that this parameter is related to the structural change and symmetry of the local environment of the Tm3+ ions in this glass.

scholarly journals Overview of a prescribed burning experiment within a boreal forest in Finland

2013 ◽  
Vol 13 (8) ◽  
pp. 21703-21763 ◽  
Author(s):  
A. Virkkula ◽  
J. Levula ◽  
T. Pohja ◽  
P. P. Aalto ◽  
P. Keronen ◽  
...  
Keyword(s):  
Boreal Forest ◽  
Radiative Forcing ◽  
Prescribed Burning ◽  
Geometric Mean ◽  
Sonic Anemometer ◽  
Ground Level ◽  
Organic Layer ◽  
Available Nitrogen ◽  
Mean Diameter

Abstract. A prescribed burning of a boreal forest was conducted on 26 June 2009 in Hyytiälä, Finland, to study aerosol and trace gas emissions from wildfires and the effects of fire on soil properties in a controlled environment. A 0.8 ha forest near the SMEAR II was cut clear; some tree trunks, all tree tops and branches were left on the ground and burned. The amount of burned organic material was ~46.8 t (i.e., ~60 t ha−1). The flaming phase lasted 2 h 15 min, the smoldering phase 3 h. Measurements were conducted on the ground with both fixed and mobile instrumentation, and from a research aircraft. In the middle of the burning area, CO2 concentration peaks were around 2000–3000 ppm above the baseline and peak vertical flow velocities were 6 ± 3 m s−1, as measured a 10-Hz 3-D sonic anemometer placed within the burn area. Peak particle number concentrations were approximately 1–2 × 106 cm−3 in the plume at a distance of 100–200 m from the burn area. The geometric mean diameter of the mode with the highest concentration was at 80 ± 1 nm during the flaming phase and in the middle of the smoldering phase but at the end of the smoldering phase the largest mode was at 122 nm. In the volume size distributions geometric mean diameter of the largest volume mode was at 153 nm during the flaming phase and at 300 nm during the smoldering phase. The lowest single-scattering albedo of the ground-level measurents was 0.7 in the flaming-phase plume and ~0.9 in the smoldering phase. The radiative forcing efficiency was negative above dark surfaces, in other words, the particles cool the atmosphere. Elevated concentrations of several VOCs (including acetonitrile which is a biomass burning marker) were observed in the smoke plume at ground level. The forest floor (i.e., richly organic layer of soil and debris, characteristic of forested land) measurements showed that VOC fluxes were generally low and consisted mainly of monoterpenes, but a clear peak of VOC flux was observed after the burning. After one year, the fluxes were nearly stabilised close to the level before the burning. The clearcutting and burning of slash increased the total long-term CO2 release from the soil, altered the soil's physical, chemical and biological properties such as increased the available nitrogen contents of the soil, which in turn, affected the level of the long-term fluxes of greenhouse gases.

scholarly journals U.K. Rainfall Data: A Long-Term Persistence Approach

2012 ◽  
Vol 51 (10) ◽  
pp. 1904-1913 ◽  
Author(s):  
Luis A. Gil-Alana
Keyword(s):  
Strong Dependence ◽  
Monthly Rainfall ◽  
Rainfall Data ◽  
Modeling Approaches ◽  
Long Run ◽  
The One

AbstractThis paper looks at the analysis of U.K. monthly rainfall data from a long-term persistence viewpoint. Different modeling approaches are considered, taking into account the strong dependence and the seasonality in the data. The results indicate that the most appropriate model is the one that presents cyclical long-run dependence with the order of integration being positive though small, and the cycles having a periodicity of about a year.

Effects of rainfall, moisture stress, and stocking rate on the persistence of white clover over 30 years

1995 ◽  
Vol 35 (7) ◽  
pp. 1039 ◽  
Author(s):  
KJ Hutchinson ◽  
KL King ◽  
DR Wilkinson
Keyword(s):  
Soil Water ◽  
White Clover ◽  
Warm Season ◽  
Late Summer ◽  
Ground Level ◽  
Moisture Stress ◽  
Smoothing Splines ◽  
Water Model ◽  
Stocking Rate

The effects of spring rainfall, critical levels of summer moisture stress, and sheep stocking rates on the persistence of white clover (Trifolium repens cv. Huia) have been evaluated in a 30-year experiment (1964-93) based on sown, well-fertilised pasture. Plant species presence was measured each year as basal cover using a vertical 10-pin frame. Hits at ground level from 800 points/plot were recorded in late September on duplicate plots, which were set-stocked at 3 rates (10, 20 reduced to 15, 30 reduced to 20 d.s.e./ha). A soil-water model based on rainfall and tank evaporation was calibrated against on-site soil water measurements (0-260 mm) and used to predict soil water (mm) for weekly time steps over 30 years. Smoothing of long-term rainfall data (SYSTAT, Lowess) showed an overall decline in warm-season rainfall (October-March), which was punctuated by above-average (1969-74) and average runs of years (1983-90). Flexible smoothing splines (SAS) were used to indicate patterns of yearly white clover presence. For all stocking treatments, there were significant declines in the presence of white clover over 3 decades. At the highest stocking rate, the recovery of white clover following the 1965 drought was poor. Late summer (January-March) moisture stress, defined as the number of weeks when soil water (0-260 mm) was <15 mm, was critical in determining white clover presence in the following spring (September). Rainfall received from October to December generally had a positive effect. These climate-based relationships reinforce the importance of stolon growth and survival as a regenerative strategy for white clover. However, over the 30 years, the species showed decreasing resilience post drought, which suggests a long-term failure of seed-based regeneration. Annual rates of soil nitrogen build-up ranged from 29 to 54 kg N/ha.year and were poorly related to white clover presence in the stocking treatments. Governing mechanisms, based on interactions between seasonal moisture stress, sheep stocking rate, interspecific plant competition, and seed pool dynamics, are proposed to explain the nature of long-term decline in white clover presence in well-fertilised, sown pastures in the Northern Tablelands of New South Wales.

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