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Solar influences on dynamical coupling between the stratosphere and troposphere
We use a simplified atmospheric general circulation model (AGCM) to investigate the response of the lower atmosphere to thermal perturbations in the lower stratosphere. The results show that generic heating of the lower stratosphere tends to weaken the sub-tropical jets and the tropospheric mean meridional circulations. The positions of the jets, and the extent of the Hadley cells, respond to the distribution of the stratospheric heating, with low latitude heating displacing them poleward, and uniform heating displacing them equatorward. The patterns of response to the low latitude heating are similar to those found to be associated with solar variability in previous observational data analysis, and to the effects of varying solar UV radiation in sophisticated AGCMs. In order to investigate the chain of causality involved in converting the stratospheric thermal forcing to a tropospheric climate signal we conduct an experiment which uses an ensemble of model spin-ups to analyse the time development of the response to an applied stratospheric perturbation. We find that the initial effect of the change in static stability at the tropopause is to reduce the eddy momentum flux convergence in this region. This is followed by a vertical transfer of the momentum forcing anomaly by an anomalous mean circulation to the surface, where it is partly balanced by surface stress anomalies. The unbalanced part drives the evolution of the vertically integrated zonal flow. We conclude that solar heating of the stratosphere may produce changes in the circulation of the troposphere even without any direct forcing below the tropopause. We suggest that the impact of the stratospheric changes on wave propagation is key to the mechanisms involved
Solar Irradiance Variability and Climate
The brightness of the Sun varies on all time scales on which it has been
observed, and there is increasing evidence that it has an influence on climate.
The amplitudes of such variations depend on the wavelength and possibly on the
time scale. Although many aspects of this variability are well established, the
exact magnitude of secular variations (going beyond a solar cycle) and the
spectral dependence of variations are under discussion. The main drivers of
solar variability are thought to be magnetic features at the solar surface. The
climate reponse can be, on a global scale, largely accounted for by simple
energetic considerations, but understanding the regional climate effects is
more difficult. Promising mechanisms for such a driving have been identified,
including through the influence of UV irradiance on the stratosphere and
dynamical coupling to the surface. Here we provide an overview of the current
state of our knowledge, as well as of the main open questions
The plastic limit of clays
The plastic limit of soils was first described by Atterberg in 1911. The thread-rolling test was standardised at the US Public Roads Bureau in the 1920s and 1930s, and has subsequently become one of the standard tests of soil mechanics. This paper reviews the original definitions of plastic limit as proposed by Atterberg, and proposes that the brittle failure observed in the plastic limit test is caused by either air entry or cavitation in the clay. Critical state soil mechanics is used to show that the observed range of undrained shear strengths of soils at plastic limit is consistent with this hypothesis. The fallacy that strength at plastic limit is a constant is highlighted, and the implications for geotechnical practice are discussed. </jats:p
Symbolic framework for linear active circuits based on port equivalence using limit variables
Published versio
Assessing the relationship between spectral solar irradiance and stratospheric ozone using Bayesian inference
We investigate the relationship between spectral solar irradiance (SSI) and
ozone in the tropical upper stratosphere. We find that solar cycle (SC) changes
in ozone can be well approximated by considering the ozone response to SSI
changes in a small number individual wavelength bands between 176 and 310 nm,
operating independently of each other. Additionally, we find that the ozone
varies approximately linearly with changes in the SSI. Using these facts, we
present a Bayesian formalism for inferring SC SSI changes and uncertainties
from measured SC ozone profiles. Bayesian inference is a powerful,
mathematically self-consistent method of considering both the uncertainties of
the data and additional external information to provide the best estimate of
parameters being estimated. Using this method, we show that, given measurement
uncertainties in both ozone and SSI datasets, it is not currently possible to
distinguish between observed or modelled SSI datasets using available estimates
of ozone change profiles, although this might be possible by the inclusion of
other external constraints. Our methodology has the potential, using wider
datasets, to provide better understanding of both variations in SSI and the
atmospheric response.Comment: 21 pages, 4 figures, Journal of Space Weather and Space Climate
(accepted), pdf version is in draft mode of Space Weather and Space Climat
Spatial and temporal variability and long-term trends in skew surges globally
Storm surges and the resulting extreme high sea levels are among the most dangerous natural disasters and are responsible for widespread social, economic and environmental consequences. Using a set of 220 tide gauges, this paper investigates the temporal variations in storm surges around the world and the spatial coherence of its variability. We compare results derived from two parameters used to represent storm surge: skew surge and the more traditional, non-tidal residual. We determine the extent of tide-surge interaction, at each study site, and find statistically significant (95% confidence) levels of tide-surge interaction at 59% of sites based on tidal level and 81% of sites based on tidal-phase. The tide-surge interaction was strongest in regions of shallow bathymetry such as the North Sea, north Australia and the Malay Peninsula. At most sites the trends in the skew surge time series were similar to those of non-tidal residuals, but where there were large differences in trends, the sites tended to have a large tidal range. Only 13% of sites had a statistically significant trend in skew surge, and of these approximately equal numbers were positive and negative. However, for trends in the non-tidal residual there were significantly more negative trends. We identified 8 regions where there were strong positive correlations in skew surge variability between sites, which meant that a regional index could be created to represent these groups of sites. Despite strong correlations between some regional skew surge indices, none were significant at the 95% level, however, at the 80% level there was significant positive correlation between the north-west Atlantic—south and the North Sea. Correlations between the regional skew surge indices and climate indices only became significant at the 80% level, where Ni?o 4 was positively correlated with the Gulf of Mexico skew surge index and negatively correlated with the east Australia skew surge index. The inclusion of autocorrelation in the calculation of correlation greatly reduced their significance, especially in the short time-series used for the regional skew surge indices. Skew surge improved the representation of storm surge magnitudes, and therefore allows a more accurate detection of changes on secular and inter-annual time scales
Optical studies of two LMC X-ray transients : RX J0544.1-7100 and RX J0520.5-6932
We report observations which confirm the identities of the optical
counterpart to the transient sources RX J0544.1-7100 and RX J0520.5-6932. The
counterparts are suggested to be a B-type stars. Optical data from the
observations carried out at ESO and SAAO, together with results from the OGLE
data base, are presented. In addition, X-ray data from the RXTE all-sky monitor
are investigated for long term periodicities. A strong suggestion for a binary
period of 24.4d is seen in RX J0520.5-6932 from the OGLE data.Comment: 6 pages, 7 figure
Assessment of some variables affecting the blanching activity of betamethasone 17-valerate cream
The effect of concentration and occlusion time on the ability of Betnovate ® cream (betamethasone 17-valerate 0.1%) to produce skin blanching was assessed. Generally, increased concentration or occlusion time produce and increase in the degree of blanching observed, however, a plateau stage is eventually reached where no further increase of blanching occurs
Implementation of a local principal curves algorithm for neutrino interaction reconstruction in a liquid argon volume
A local principal curve algorithm has been implemented in three dimensions
for automated track and shower reconstruction of neutrino interactions in a
liquid argon time projection chamber. We present details of the algorithm and
characterise its performance on simulated data sets.Comment: 14 pages, 17 figures; typing correction to Eq 5, the definition of
the local covariance matri
Vascular endothelial growth factor directly inhibits primitive neural stem cell survival but promotes definitive neural stem cell survival
There are two types of neural stem cells (NSCs). Primitive NSCs [leukemia inhibitory factor (LIF) dependent but exogenous fibroblast growth factor (FGF) 2 independent] can be derived from mouse embryonic stem (ES) cells in vitro and from embryonic day 5.5 (E5.5) to E7.5 epiblast and E7.5-E8.5 neuroectoderm in vivo. Definitive NSCs (LIF independent but FGF2 dependent) first appear in the E8.5 neural plate and persist throughout life. Primitive NSCs give rise to definitive NSCs. Loss and gain of functions were used to study the role of vascular endothelial growth factor (VEGF)-A and its receptor, Flk1, in NSCs. The numbers of Flk1 knock-out mice embryo-derived and ES cell-derived primitive NSCs were increased because of the enhanced survival of primitive NSCs. In contrast, neural precursor-specific, Flk1 conditional knock-out mice-derived, definitive NSCs numbers were decreased because of the enhanced cell death of definitive NSCs. These effects were not observed in cells lacking Flt1, another VEGF receptor. In addition, the cell death stimulated by VEGF-A of primitive NSC and the cell survival stimulated by VEGF-A of definitive NSC were blocked by Flk1/Fc-soluble receptors and VEGF-A function-blocking antibodies. These VEGF-A phenotypes also were blocked by inhibition of the downstream effector nuclear factor kappa B (NF-kappa B). Thus, both the cell death of primitive NSC and the cell survival of definitive NSC induced by VEGF-A stimulation are mediated by bifunctional NF-kappa B effects. In conclusion, VEGF-A function through Flk1 mediates survival (and not proliferative or fate change) effects on NSCs, specifically
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