1,620 research outputs found
Where do winds come from? A new theory on how water vapor condensation influences atmospheric pressure and dynamics
Phase transitions of atmospheric water play a ubiquitous role in the Earth's
climate system, but their direct impact on atmospheric dynamics has escaped
wide attention. Here we examine and advance a theory as to how condensation
influences atmospheric pressure through the mass removal of water from the gas
phase with a simultaneous account of the latent heat release. Building from the
fundamental physical principles we show that condensation is associated with a
decline in air pressure in the lower atmosphere. This decline occurs up to a
certain height, which ranges from 3 to 4 km for surface temperatures from 10 to
30 deg C. We then estimate the horizontal pressure differences associated with
water vapor condensation and find that these are comparable in magnitude with
the pressure differences driving observed circulation patterns. The water vapor
delivered to the atmosphere via evaporation represents a store of potential
energy available to accelerate air and thus drive winds. Our estimates suggest
that the global mean power at which this potential energy is released by
condensation is around one per cent of the global solar power -- this is
similar to the known stationary dissipative power of general atmospheric
circulation. We conclude that condensation and evaporation merit attention as
major, if previously overlooked, factors in driving atmospheric dynamics
Comment on "The Tropospheric Land-Sea Warming Contrast as the Driver of Tropical Sea Level Pressure Changes" by Bayr and Dommenget
T Bayr and D Dommenget [J. Climate 26 (2013) 1387] proposed a model of
temperature-driven air redistribution to quantify the ratio between changes of
sea level pressure and mean tropospheric temperature in the
tropics. This model assumes that the height of the tropical troposphere is
isobaric. Here problems with this model are identified. A revised relationship
between and is derived governed by two parameters -- the isobaric
and isothermal heights -- rather than just one. Further insight is provided by
the model of R S Lindzen and S Nigam [J. Atmos. Sci. 44 (1987) 2418], which was
the first to use the concept of isobaric height to relate tropical to air
temperature, and did this by assuming that isobaric height is always around 3
km and isothermal height is likewise near constant. Observational data,
presented here, show that neither of these heights is spatially universal nor
do their mean values match previous assumptions. Analyses show that the ratio
of the long-term changes in and associated with land-sea
temperature contrasts in a warming climate -- the focus of Bayr and Dommenget
[2013] -- is in fact determined by the corresponding ratio of spatial
differences in the annual mean and . The latter ratio, reflecting
lower pressure at higher temperature in the tropics, is dominated by meridional
pressure and temperature differences rather than by land-sea contrasts.
Considerations of isobaric heights are shown to be unable to predict either
spatial or temporal variation in . As noted by Bayr and Dommenget [2013],
the role of moisture dynamics in generating sea level pressure variation
remains in need of further theoretical investigations.Comment: 26 pages, 11 figures. arXiv admin note: text overlap with
arXiv:1404.101
Pattern of relapse and treatment response in WNT-activated medulloblastoma
Over the past decade, wingless-activated (WNT) medulloblastoma has been identified as a candidate for therapy de-escalation based on excellent survival; however, a paucity of relapses has precluded additional analyses of markers of relapse. To address this gap in knowledge, an international cohort of 93 molecularly confirmed WNT MB was assembled, where 5-year progression-free survival is 0.84 (95%, 0.763-0.925) with 15 relapsed individuals identified. Maintenance chemotherapy is identified as a strong predictor of relapse, with individuals receiving high doses of cyclophosphamide or ifosphamide having only one very late molecularly confirmed relapse (p = 0.032). The anatomical location of recurrence is metastatic in 12 of 15 relapses, with 8 of 12 metastatic relapses in the lateral ventricles. Maintenance chemotherapy, specifically cumulative cyclophosphamide doses, is a significant predictor of relapse across WNT MB. Future efforts to de-escalate therapy need to carefully consider not only the radiation dose but also the chemotherapy regimen and the propensity for metastatic relapses
Unravelling wild carrot differentiation in Europe: preliminary data on a candidate gene approach
Carrot is an outcrossing species and levels of gene flow between populations,
and even between wild and domesticated relatives, are expected to be high. Cases of
natural hybridization and introgression of crops and wild relatives have been
reported. Have these events diluted any putative habitat-adapted genotypes? In other
words, can we still find a correlation between wild carrot genotypes and
regional/local environment? We have chosen to start addressing this question using a
member of the alternative oxidase (AOX) gene family. AOX genes seem to be linked to
all kinds of abiotic and biotic stress reactions. Wild carrots were sampled in an
environmental gradient across Western Europe. This gradient included sampling
points with more deviating conditions, such as Sierra de Guadarrama or the central
Pyrenees and the French Massif Central. Phylogenetic reconstruction on this
molecular marker is to be combined with geographic, climatic, and ecological
evidence. So far, the preliminary results suggest the existence of a biogeographical
barrier at the Pyrenees, and higher gene diversity than initially expected. From an
applied point of view, diversity of functional traits is much more relevant than species
diversity. Gene transfer from wild to cultivated plants has contributed to the evolution
of crop species. Providing that deterioration of genetic resources and biodiversity loss
have not been drastic, gene transfer from wild plants has the potential to further
contribute to a (targeted) improvement of cultivars.info:eu-repo/semantics/publishedVersio
Radiatively induced leptogenesis in a minimal seesaw model
We study the possibility that the baryon asymmetry of the universe is
generated in a minimal seesaw scenario where two right-handed Majorana
neutrinos with degenerate masses are added to the standard model particle
content. In the usual framework of thermal leptogenesis, a nonzero
asymmetry can be obtained through the mass splitting induced by the running of
the heavy Majorana neutrino masses from their degeneracy scale down to the
seesaw scale. Although, in the light of the present neutrino oscillation data,
the produced baryon asymmetry turns out to be smaller than the experimental
value, the present mechanism could be viable in simple extensions of the
standard model.Comment: 6 pages, 2 figures, uses RevTeX4, calculations improved, comments
adde
Heat engines and heat pumps in a hydrostatic atmosphere: How surface pressure and temperature constrain wind power output and circulation cell size
The kinetic energy budget of the atmosphere's meridional circulation cells is
analytically assessed. In the upper atmosphere kinetic energy generation grows
with increasing surface temperature difference \$\Delta T_s\$ between the cold
and warm ends of a circulation cell; in the lower atmosphere it declines. A
requirement that kinetic energy generation is positive in the lower atmosphere
limits the poleward cell extension \$L\$ of Hadley cells via a relationship
between \$\Delta T_s\$ and surface pressure difference \$\Delta p_s\$: an upper
limit exists when \$\Delta p_s\$ does not grow with increasing \$\Delta T_s\$.
This pattern is demonstrated here using monthly data from MERRA re-analysis.
Kinetic energy generation along air streamlines in the boundary layer does not
exceed \$40\$~J~mol\$^{-1}\$; it declines with growing \$L\$ and reaches zero
for the largest observed \$L\$ at 2~km height. The limited meridional cell size
necessitates the appearance of heat pumps -- circulation cells with negative
work output where the low-level air moves towards colder areas. These cells
consume the positive work output of the heat engines -- cells where the
low-level air moves towards the warmer areas -- and can in theory drive the
global efficiency of atmospheric circulation down to zero. Relative
contributions of \$\Delta p_s\$ and \$\Delta T_s\$ to kinetic energy generation
are evaluated: \$\Delta T_s\$ dominates in the upper atmosphere, while \$\Delta
p_s\$ dominates in the lower. Analysis and empirical evidence indicate that the
net kinetic power output on Earth is dominated by surface pressure gradients,
with minor net kinetic energy generation in the upper atmosphere. The role of
condensation in generating surface pressure gradients is discussed.Comment: 26 pages, 9 figures, 2 tables; re-organized presentation, more
discussion and a new figure (Fig. 4) added; in Fig. 3 the previously
invisible dots (observations) can now be see
Enhancement of the ferromagnetic order of graphite after sulphuric acid treatment
We have studied the changes in the ferromagnetic behavior of graphite powder
and graphite flakes after treatment with diluted sulphuric acid. We show that
this kind of acid treatment enhances substantially the ferromagnetic
magnetization of virgin graphite micrometer size powder as well as in graphite
flakes. The anisotropic magnetoresistance (AMR) amplitude at 300 K measured in
a micrometer size thin graphite flake after acid treatment reaches values
comparable to polycrystalline cobalt.Comment: 3.2 pages, 4 figure
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