30 research outputs found
Interannual variation patterns of total ozone and lower stratospheric temperature in observations and model simulations
We report results from a multiple linear regression
analysis of long-term total ozone observations (1979 to
2000, by TOMS/SBUV), of temperature reanalyses (1958
to 2000, NCEP), and of two chemistry-climate model simulations
(1960 to 1999, by ECHAM4.L39(DLR)/CHEM
(=E39/C), and MAECHAM4-CHEM). The model runs are
transient experiments, where observed sea surface temperatures,
increasing source gas concentrations (CO2, CFCs,
CH4, N2O, NOx), 11-year solar cycle, volcanic aerosols
and the quasi-biennial oscillation (QBO) are all accounted
for. MAECHAM4-CHEM covers the atmosphere from the
surface up to 0.01 hPa ( 80 km). For a proper representation
of middle atmosphere (MA) dynamics, it includes
a parametrization for momentum deposition by dissipating
gravity wave spectra. E39/C, on the other hand, has its top
layer centered at 10 hPa ( 30 km). It is targeted on processes
near the tropopause, and has more levels in this region.
Despite some problems, both models generally reproduce
the observed amplitudes and much of the observed lowlatitude
patterns of the various modes of interannual variability
in total ozone and lower stratospheric temperature. In
most aspects MAECHAM4-CHEM performs slightly better
than E39/C. MAECHAM4-CHEM overestimates the longterm
decline of total ozone, whereas E39/C underestimates
the decline over Antarctica and at northern mid-latitudes.
The true long-term decline in winter and spring above the
Correspondence to: W. Steinbrecht
([email protected])
Arctic may be underestimated by a lack of TOMS/SBUV
observations in winter, particularly in the cold 1990s. Main
contributions to the observed interannual variations of total
ozone and lower stratospheric temperature at 50 hPa come
from a linear trend (up to −10 DU/decade at high northern
latitudes, up to −40 DU/decade at high southern latitudes,
and around −0.7 K/decade over much of the globe), from
the intensity of the polar vortices (more than 40 DU, or 8 K
peak to peak), the QBO (up to 20 DU, or 2 K peak to peak),
and from tropospheric weather (up to 20 DU, or 2 K peak
to peak). Smaller variations are related to the 11-year solar
cycle (generally less than 15 DU, or 1 K), or to ENSO (up
to 10 DU, or 1 K). These observed variations are replicated
well in the simulations. Volcanic eruptions have resulted in
sporadic changes (up to −30 DU, or +3 K). At low latitudes,
patterns are zonally symmetric. At higher latitudes, however,
strong, zonally non-symmetric signals are found close
to the Aleutian Islands or south of Australia. Such asymmetric
features appear in the model runs as well, but often
at different longitudes than in the observations. The results
point to a key role of the zonally asymmetric Aleutian (or
Australian) stratospheric anti-cyclones for interannual variations
at high-latitudes, and for coupling between polar vortex
strength, QBO, 11-year solar cycle and ENSO
Interannual variation patterns of total ozone and temperature in observations and model simulations
We report results from a multiple linear regression analysis of long-term total ozone observations (1979 to 2000, by TOMS/SBUV), of temperature reanalyses (1958 to 2000, NCEP), and of two chemistry-climate model simulations (1960 to 1999, by ECHAM4.L39(DLR)/CHEM (=E39/C), and MAECHAM4-CHEM). The model runs are transient experiments, where observed sea surface temperatures, increasing source gas concentrations (CO2, CFCs, CH4, N2O, NOx), 11-year solar cycle, volcanic aerosols and the quasi-biennial oscillation (QBO) are all accounted for. MAECHAM4-CHEM covers the atmosphere from the surface up to 0.01 hPa (≈80 km). For a proper representation of middle atmosphere (MA) dynamics, it includes a parametrization for momentum deposition by dissipating gravity wave spectra. E39/C, on the other hand, has its top layer centered at 10 hPa (≈30 km). It is targeted on processes near the tropopause, and has more levels in this region. Despite some problems, both models generally reproduce the observed amplitudes and much of the observed low-latitude patterns of the various modes of interannual variability in total ozone and lower stratospheric temperature. In most aspects MAECHAM4-CHEM performs slightly better than E39/C. MAECHAM4-CHEM overestimates the long-term decline of total ozone, whereas underestimates the decline over Antarctica and at northern mid-latitudes. The true long-term decline in winter and spring above the Arctic may be underestimated by a lack of TOMS/SBUV observations in winter, particularly in the cold 1990s. Main contributions to the observed interannual variations of total ozone and lower stratospheric temperature at 50 hPa come from a linear trend (up to -10 DU/decade at high northern latitudes, up to -40 DU/decade at high southern latitudes, and around -0.7 K/decade over much of the globe), from the intensity of the polar vortices (more than 40 DU, or 8 K peak to peak), the QBO (up to 20 DU, or 2 K peak to peak), and from tropospheric weather (up to 20 DU, or 2 K peak to peak). Smaller variations are related to the 11-year solar cycle (generally less than 15 DU, or 1 K), or to ENSO (up to 10 DU, or 1 K). These observed variations are replicated well in the simulations. Volcanic eruptions have resulted in sporadic changes (up to -30 DU, or +3 K). At low latitudes, patterns are zonally symmetric. At higher latitudes, however, strong, zonally non-symmetric signals are found close to the Aleutian Islands or south of Australia. Such asymmetric features appear in the model runs as well, but often at different longitudes than in the observations. The results point to a key role of the zonally asymmetric Aleutian (or Australian) stratospheric anti-cyclones for interannual variations at high-latitudes, and for coupling between polar vortex strength, QBO, 11-year solar cycle and ENSO
Interannual variation patterns of total ozone and lower stratospheric temperature in observations and model simulations
We report results from a multiple linear regression analysis of long-term total ozone observations (1979 to 2000, by TOMS/SBUV), of temperature reanalyses (1958 to 2000, NCEP), and of two chemistry-climate model simulations (1960 to 1999, by ECHAM4.L39(DLR)/CHEM (=E39/C), and MAECHAM4-CHEM). The model runs are transient experiments, where observed sea surface temperatures, increasing source gas concentrations (CO<sub>2</sub>, <i>CFC</i>s, CH<sub>4</sub>, N<sub>2</sub>O, NO<sub>x</sub>), 11-year solar cycle, volcanic aerosols and the quasi-biennial oscillation (QBO) are all accounted for. MAECHAM4-CHEM covers the atmosphere from the surface up to 0.01 hPa (≈80 km). For a proper representation of middle atmosphere (MA) dynamics, it includes a parametrization for momentum deposition by dissipating gravity wave spectra. E39/C, on the other hand, has its top layer centered at 10 hPa (≈30 km). It is targeted on processes near the tropopause, and has more levels in this region. Despite some problems, both models generally reproduce the observed amplitudes and much of the observed low-latitude patterns of the various modes of interannual variability in total ozone and lower stratospheric temperature. In most aspects MAECHAM4-CHEM performs slightly better than E39/C. MAECHAM4-CHEM overestimates the long-term decline of total ozone, whereas underestimates the decline over Antarctica and at northern mid-latitudes. The true long-term decline in winter and spring above the Arctic may be underestimated by a lack of TOMS/SBUV observations in winter, particularly in the cold 1990s. Main contributions to the observed interannual variations of total ozone and lower stratospheric temperature at 50 hPa come from a linear trend (up to -10 DU/decade at high northern latitudes, up to -40 DU/decade at high southern latitudes, and around -0.7 K/decade over much of the globe), from the intensity of the polar vortices (more than 40 DU, or 8 K peak to peak), the QBO (up to 20 DU, or 2 K peak to peak), and from tropospheric weather (up to 20 DU, or 2 K peak to peak). Smaller variations are related to the 11-year solar cycle (generally less than 15 DU, or 1 K), or to ENSO (up to 10 DU, or 1 K). These observed variations are replicated well in the simulations. Volcanic eruptions have resulted in sporadic changes (up to -30 DU, or +3 K). At low latitudes, patterns are zonally symmetric. At higher latitudes, however, strong, zonally non-symmetric signals are found close to the Aleutian Islands or south of Australia. Such asymmetric features appear in the model runs as well, but often at different longitudes than in the observations. The results point to a key role of the zonally asymmetric Aleutian (or Australian) stratospheric anti-cyclones for interannual variations at high-latitudes, and for coupling between polar vortex strength, QBO, 11-year solar cycle and ENSO
Hollow carbon spheres as an efficient dopant for enhancing critical current density of MgB2 based tapes
A significant enhancement of Jc and Hirr in MgB2 tapes has been achieved by
the in situ powder-in-tube method utilizing hollow carbon spheres (HCS) as
dopants. At 4.2 K, the transport Jc for the 850C sintered samples reached
3.1x10^4, and 1.4x10^4 A/cm^2 at 10 and 12 T, respectively, and were better
than those of optimal nano-SiC doped tapes. Furthermore, the Hirr for doped
sample was raised up to 16.8 T at 10 K due to the carbon substitution effect.
The results demonstrate that HCS is one of the most promising dopants besides
nano-carbon and SiC for the enhancement of current capacity for MgB2 in high
fields.Comment: 14 pages, 5 figure