174 research outputs found
Gravitational Effects in Supersymmetric Domain Wall Backgrounds
A recent study of supersymmetric domain walls in supergravity theories
revealed a new class of domain walls interpolating between supersymmetric vacua
with different non-positive cosmological constants. We classify three classes
of domain wall configurations and study the geodesic structure of the induced
space-time. Motion of massive test particles in such space-times shows that
these walls are always repulsive from the anti-deSitter (AdS) side, while on
the Minkowski side test particles feel no force. Freely falling particles far
away from a wall in an AdS vacuum experience a constant proper acceleration,
\ie\ they are Rindler particles. A new coordinate system for discussing AdS
space-time is presented which eliminates the use of a periodic time-like
coordinate.Comment: 13 pages + 4 figures (not included
Relating the diffusive salt flux just below the ocean surface to boundary freshwater and salt fluxes
We detail the physical means whereby boundary transfers of freshwater and salt induce diffusive fluxes of salinity. Our considerations focus on the kinematic balance between the diffusive fluxes of salt and freshwater, with this balance imposed by mass conservation for an element of seawater. The flux balance leads to a specific form for the diffusive salt flux immediately below the ocean surface and, in the Boussinesq approximation, to a specific form for the salinity flux. This note clarifies conceptual and formulational ambiguities in the literature concerning the surface boundary condition for the salinity equation and for the contribution of freshwater to the buoyancy budget
Local Drivers of Marine Heatwaves: A Global Analysis With an Earth System Model
Marine heatwaves (MHWs) are periods of extreme warm ocean temperatures that can have devastating impacts on marine organisms and socio-economic systems. Despite recent advances in understanding the underlying processes of individual events, a global view of the local oceanic and atmospheric drivers of MHWs is currently missing. Here, we use daily-mean output of temperature tendency terms from a comprehensive fully coupled coarse-resolution Earth system model to quantify the main local processes leading to the onset and decline of surface MHWs in different seasons. The onset of MHWs in the subtropics and mid-to-high latitudes is primarily driven by net ocean heat uptake associated with a reduction of latent heat loss in all seasons, increased shortwave heat absorption in summer and reduced sensible heat loss in winter, dampened by reduced vertical mixing from the non-local portion of the K-Profile Parameterization boundary layer scheme (KPP) especially in summer. In the tropics, ocean heat uptake is reduced and lowered vertical local mixing and diffusion cause the warming. In the subsequent decline phase, increased ocean heat loss to the atmosphere due to enhanced latent heat loss in all seasons together with enhanced vertical local mixing and diffusion in the high latitudes during summer dominate the temperature decrease globally. The processes leading to the onset and decline of MHWs are similar for short and long MHWs, but there are differences in the drivers between summer and winter. Different types of MHWs with distinct driver combinations are identified within the large variability among events. Our analysis contributes to a better understanding of MHW drivers and processes and may therefore help to improve the prediction of high-impact marine heatwaves
On Pacific Subtropical Cell Variability over the Second Half of the Twentieth Century
Abstract
The evolution of the Pacific subtropical cells (STC) is presented for the period 1948â2007. Using ocean models of different resolutions forced with interannually varying atmospheric forcing datasets, the mechanisms responsible for the observed STC weakening and late recovery during the period of study are analyzed. As a result of the STC weakening (strengthening), warming (cooling) trends are found in the equatorial Pacific sea surface temperatures (SSTs). Model results agree well with observed estimates of STC transport, STC convergence, and equatorial SST anomalies. It is shown that subtropical atmospheric variability is the primary driver of the STC and equatorial SST low-frequency evolution and is responsible for both the slowdown during the second half of the twentieth century and the rebound at the end of the century. Subtropically forced STC variability is identified as a major player in the generation of equatorial Pacific decadal SST anomalies, pacing tropical Pacific natural climate variability on interdecadal time scales, as observed in historical records. The natural mode of variability has implications for the evolution of equatorial SST in the coming decades under the concomitant effects of climate change
Global Cascade of Kinetic Energy in the Ocean and the Atmospheric Imprint
We present the first estimate for the ocean's global scale-transfer of
kinetic energy (KE), across scales from 10~km to 40000~km. We show the
existence of oceanic KE transfer between gyre-scales and mesoscales induced by
the atmosphere's Hadley, Ferrel, and polar cells, and intense downscale KE
transfer associated with the Inter-Tropical Convergence Zone. We report peak
upscale transfer of 300 GigaWatts across mesoscales of 120~km in size, roughly
1/3rd the energy input by winds into the oceanic general circulation. This
"cascade" penetrates almost the entire water column, with nearly three quarters
of it occurring south of 15S. The mesoscale cascade has a self-similar
seasonal cycle with characteristic lag-time of days per
octave of length-scales such that transfer across 50~km peaks in spring while
transfer across 500~km peaks in summer. KE content of those mesoscales follows
the same self-similar cycle but peaks days after the peak
cascade, suggesting that energy transferred across a scale is primarily
deposited at a scale 4 larger
Exploring the non-stationarity of coastal sea level probability distributions
Studies agree on a significant global mean sea level rise in the 20th century
and its recent 21st century acceleration in the satellite record. At regional
scale, the evolution of sea level probability distributions is often assumed to
be dominated by changes in the mean. However, a quantification of changes in
distributional shapes in a changing climate is currently missing. To this end,
we propose a novel framework quantifying significant changes in probability
distributions from time series data. The framework first quantifies linear
trends in quantiles through quantile regression. Quantile slopes are then
projected onto a set of four polynomials quantifying how such
changes can be explained by shifts in the first four statistical
moments. The framework proposed is theoretically founded, general and can be
applied to any climate observable with close-to-linear changes in
distributions. We focus on observations and a coupled climate model (GFDL-CM4).
In the historical period, trends in coastal daily sea level have been driven
mainly by changes in the mean and can therefore be explained by a shift of the
distribution with no change in shape. In the modeled world, robust changes in
higher order moments emerge with increasing concentration. Such
changes are driven in part by ocean circulation alone and get amplified by sea
level pressure fluctuations, with possible consequences for sea level extremes
attribution studies
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