88 research outputs found
Extension and its characteristics of ECRH plasma in the LHD
One of the main objectives of the LHD is to extend the plasma confinement
database for helical systems and to demonstrate such extended plasma
confinement properties to be sustained in steady state. Among the various
plasma parameter regimes, the study of confinement properties in the
collisionless regime is of particular importance. Electron cyclotron resonance
heating (ECRH) has been extensively used for these confinement studies of the
LHD plasma from the initial operation. The system optimizations including the
modification of the transmission and antenna system are performed with the
special emphasis on the local heating properties. As the result, central
electron temperature of more than 10 keV with the electron density of 0.6 x
10 m is achieved near the magnetic axis. The electron temperature
profile is characterized by a steep gradient similar to those of an internal
transport barrier observed in tokamaks and stellarators. 168 GHz ECRH system
demonstrated efficient heating at over the density more than 1.0 x 10
m. CW ECRH system is successfully operated to sustain 756 s discharge.Comment: 12th International Congress on Plasma Physics, 25-29 October 2004,
Nice (France
Northern Hemisphere contrail properties derived from Terra and Aqua MODIS data for 2006 and 2012
Linear contrail coverage, optical property, and radiative
forcing data over the Northern Hemisphere (NH) are derived from a year
(2012) of Terra and Aqua Moderate-resolution Imaging Spectroradiometer (MODIS)
imagery and compared with previously published 2006 results (Duda et al.,
2013; Bedka et al., 2013; Spangenberg et al., 2013) using a consistent
retrieval methodology. Differences in the observed Terra-minus-Aqua screened contrail
coverage and patterns in the 2012 annual-mean air traffic estimated with
respect to satellite overpass time suggest that most contrails detected by
the contrail detection algorithm (CDA) form approximately 2 h before
overpass time. The 2012 screened NH contrail coverage (Mask B) shows a
relative 3 % increase compared to 2006 data for Terra and increases by almost
7 % for Aqua, although the differences are not expected to be statistically
significant. A new post-processing algorithm added to the contrail mask
processing estimated that the total contrail cirrus coverage visible in the
MODIS imagery may be 3 to 4 times larger than the linear contrail
coverage detected by the CDA. This estimate is similar in magnitude to the
spreading factor estimated by Minnis et al. (2013). Contrail property
retrievals of the 2012 data indicate that both contrail optical depth and
contrail effective diameter decreased approximately 10 % between 2006 and
2012. The decreases may be attributed to better background cloudiness
characterization, changes in the waypoint screening, or changes in contrail
temperature. The total mean contrail radiative forcings (TCRFs) for all 2012
Terra observations were −6.3, 14.3, and 8.0 mW m−2 for the shortwave
(SWCRF), longwave (LWCRF), and net forcings, respectively. These values are
approximately 20 % less than the corresponding 2006 Terra estimates. The
decline in TCRF results from the decrease in normalized CRF, partially
offset by the 3 % increase in overall contrail coverage in 2012. The TCRFs
for 2012 Aqua are similar, −6.4, 15.5, and 9.0 mW m−2 for shortwave,
longwave, and net radiative forcing. The strong correlation between the
relative changes in both total SWCRF and LWCRF between 2006 and 2012 and the
corresponding relative changes in screened contrail coverage over each air
traffic region suggests that regional changes in TCRF from year to year are
dominated by year-to-year changes in contrail coverage over each area.</p
Perennial snow and ice variations (2000–2008) in the Arctic circumpolar land area from satellite observations
Perennial snow and ice (PSI) extent is an important parameter of mountain environments with regard to its involvement in the hydrological cycle and the surface energy budget. We investigated interannual variations of PSI in nine mountain regions of interest (ROI) between 2000 and 2008. For that purpose, a novel MODIS data set processed at the Canada Centre for Remote Sensing at 250 m spatial resolution was utilized. The extent of PSI exhibited significant interannual variations, with coefficients of variation ranging from 5% to 81% depending on the ROI. A strong negative relationship was found between PSI and positive degree‐days (threshold 0°C) during the summer months in most ROIs, with linear correlation coefficients (r) being as low as r = −0.90. In the European Alps and Scandinavia, PSI extent was significantly correlated with annual net glacier mass balances, with r = 0.91 and r = 0.85, respectively, suggesting that MODIS‐derived PSI extent may be used as an indicator of net glacier mass balances. Validation of PSI extent in two land surface classifications for the years 2000 and 2005, GLC‐2000 and Globcover, revealed significant discrepancies of up to 129% for both classifications. With regard to the importance of such classifications for land surface parameterizations in climate and land surface process models, this is a potential source of error to be investigated in future studies. The results presented here provide an interesting insight into variations of PSI in several ROIs and are instrumental for our understanding of sensitive mountain regions in the context of global climate change assessment
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