806 research outputs found
HATCHLING SEX RATIOS AND LOCOMOTOR PERFORMANCE OF MIDLAND PAINTED TURTLES (CHRYSEMYS PICTA MARGINATA)
The primary objectives of this study were to understand how canopy cover and nest temperatures affect hatchling sex ratios and locomotor performance (i.e., swimming sprint speed and righting response) of Chrysemys picta marginata nests. Seventeen nests were monitored with temperature data-loggers during the 2009 nesting season and found to contain 100% male-biased clutches with a mean nest temperature range of 20.0–24.0°C during the thermosensitive period (TSP). The percentage of canopy cover over each nest was inversely and significantly correlated with mean nest temperatures experienced during the TSP. Mean nest temperatures (MNT) did not have a statistical effect on either measure of locomotor performance; however, there was an observed trend toward increased performance with increased MNT
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
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
More trees for more water in drylands: myths and opportunities
The mechanisms by which trees influence water availability remain incompletely understood, but the last two decades have brought astonishing advances. We already know enough to see major opportunities to improve water security in tropical drylands through tree cover, while also yielding the many other benefits that trees provide
Propanil Exposure Induces Delayed but Sustained Abrogation of Cell-Mediated Immunity through Direct Interference with Cytotoxic T-Lymphocyte Effectors
The postemergent herbicide propanil (PRN; also known as 3,4-dichloropropionanilide) is used on rice and wheat crops and has well-known immunotoxic effects on various compartments of the immune system, including T-helper lymphocytes, B lymphocytes, and macrophages. It is unclear, however, whether PRN also adversely affects cytotoxic T lymphocytes (CTLs), the primary (1°) effectors of cell-mediated immunity. In this study we examined both the direct and indirect effects of PRN exposure on CTL activation and effector cell function to gauge its likely impact on cell-mediated immunity. Initial experiments addressed whether PRN alters the class I major histocompatibility complex (MHC) pathway for antigen processing and presentation by antigen-presenting cells (APCs), thereby indirectly affecting effector function. These experiments demonstrated that PRN does not impair the activation of CTLs by PRN-treated APCs. Subsequent experiments addressed whether PRN treatment of CTLs directly inhibits their activation and revealed that 1° alloreactive CTLs exposed to PRN are unimpaired in their proliferative response and only marginally inhibited in their lytic activity. Surprisingly, secondary stimulation of these alloreactive CTL effectors, however, even in the absence of further PRN exposure, resulted in complete abrogation of CTL lytic function and a delayed but significant long-term effect on CTL responsiveness. These findings may have important implications for the diagnosis and clinical management of anomalies of cell-mediated immunity resulting from environmental exposure to various herbicides and other pesticides
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