2,888 research outputs found
Interhemispheric structure and variability of the 5-day planetary wave from meteor radar wind measurements
A study of the quasi-5-day wave (5DW) was performed using meteor radars at conjugate latitudes in the Northern and Southern hemispheres. These radars are located at Esrange, Sweden (68° N) and Juliusruh, Germany (55° N) in the Northern Hemisphere, and at Tierra del Fuego, Argentina (54° S) and Rothera Station, Antarctica (68° S) in the Southern Hemisphere. The analysis was performed using data collected during simultaneous measurements by the four radars from June 2010 to December 2012 at altitudes from 84 to 96 km. The 5DW was found to exhibit significant short-term, seasonal, and interannual variability at all sites. Typical events had planetary wave periods that ranged between 4 and 7 days, durations of only a few cycles, and infrequent strongly peaked variances and covariances. Winds exhibited rotary structures that varied strongly among sites and between events, and maximum amplitudes up to ~ 20 m sâ1. Mean horizontal velocity covariances tended to be largely negative at all sites throughout the interval studied
Recommended from our members
Interhemispheric structure and variability of the 5-day planetary wave from meteor radar wind measurements
A study of the quasi-5-day wave (5DW) was performed using meteor radars at conjugate latitudes in the Northern and Southern hemispheres. These radars are located at Esrange, Sweden (68° N) and Juliusruh, Germany (55° N) in the Northern Hemisphere, and at Tierra del Fuego, Argentina (54° S) and Rothera Station, Antarctica (68° S) in the Southern Hemisphere. The analysis was performed using data collected during simultaneous measurements by the four radars from June 2010 to December 2012 at altitudes from 84 to 96 km. The 5DW was found to exhibit significant short-term, seasonal, and interannual variability at all sites. Typical events had planetary wave periods that ranged between 4 and 7 days, durations of only a few cycles, and infrequent strongly peaked variances and covariances. Winds exhibited rotary structures that varied strongly among sites and between events, and maximum amplitudes up to ~ 20 m sâ1. Mean horizontal velocity covariances tended to be largely negative at all sites throughout the interval studied
Recommended from our members
The varieties of remembered experience: Moving memory beyond the bounded self
We review the contributions to this Special Issue that highlight the diverse ways in which memory takes place that go beyond the standard personal autobiographical memory and its reliance on internal imagery. We look at how contributors explore a highly individual memory of trauma and re-consider it as a complex, socially contested phenomenon. We next turn to a discussion of shared memory within dyads and then look at a contribution that examines bodily and gestural alignment during shared recollection among group members and/or families. From there, contributors raise considerations of collective memory in prisoner-of-war survivors and among football fans attending a World Cup event. The next contribution illustrates how collective forgetting creates social bonds in a similar manner to collective remembering. Finally, we show how the boundaries of memory are being stretched by digital technology through its influence on how we recall and share memories. Methodological innovations are also discussed
The Physics of Bodily Tides in Terrestrial Planets, and the Appropriate Scales of Dynamical Evolution
Any model of tides is based on a specific hypothesis of how lagging depends
on the tidal-flexure frequency. For example, Gerstenkorn (1955), MacDonald
(1964), and Kaula (1964) assumed constancy of the geometric lag angle, while
Singer (1968) and Mignard (1979, 1980) asserted constancy of the time lag.
Thus, each of these two models was based on a certain law of scaling of the
geometric lag.
The actual dependence of the geometric lag on the frequency is more
complicated and is determined by the rheology of the planet. Besides, each
particular functional form of this dependence will unambiguously fix the
appropriate form of the frequency dependence of the tidal quality factor, Q.
Since at present we know the shape of the dependence of Q upon the frequency,
we can reverse our line of reasoning and single out the appropriate actual
frequency-dependence of the angular lag. This dependence turns out to be
different from those employed hitherto, and it entails considerable alterations
in the time scales of the tide-generated dynamical evolution. Phobos' fall on
Mars is an example we consider.Comment: arXiv admin note: substantial text overlap with
arXiv:astro-ph/060552
Diversity and Evolution of Myxobacterial Type IV Pilus Systems
Type IV pili (T4P) are surface-exposed protein fibers that play key roles in the bacterial life cycle via surface attachment/adhesion, biofilm formation, motility, and development. The order Myxococcales (myxobacteria) are members of the class Deltaproteobacteria and known for their large genome size and complex social behaviors, including gliding motility, fruiting body formation, biofilm production, and prey hunting. Myxococcus xanthus, the best-characterized member of the order, relies on the appropriate expression of 17 type IVa (T4aP) genes organized in a single cluster plus additional genes (distributed throughout the genome) for social motility and development. Here, we compared T4aP genes organization within the myxobacteria to understand their evolutionary origins and diversity. We found that T4aP genes are organized as large clusters in suborder Cystobacterineae, whereas in other two suborders Sorangiineae and Nannocystineae, these genes are dispersed throughout the genome. Based on the genomic organization, the phylogeny of conserved proteins, and synteny studies among 28 myxobacterial and 66 Proteobacterial genomes, we propose an evolutionary model for the origin of myxobacterial T4aP genes independently from other orders in class Deltaproteobacteria. Considering a major role for T4P, this study further proposes the origins and evolution of social motility in myxobacteria and provides a foundation for understanding how complex-behavioral traits, such as gliding motility, multicellular development, etc., might have evolved in this diverse group of complex organisms
How Chinaâs Options Will Determine GlobalWarming
Carbon dioxide emissions, global average temperature, atmospheric CO2
concentrations, and surface ocean mixed layer acidity are extrapolated using analyses
calibrated against extensive time series data for nine global regions. Extrapolation of
historical trends without policy-driven limitations has China responsible for about half of
global CO2 emissions by the middle of the twenty-first century. Results are presented
for three possible actions taken by China to limit global average temperature increase to
levels it considers to be to its advantage: (1) Help develop low-carbon energy technology
broadly competitive with unbridled carbon emissions from burning fossil fuels; (2) Entice
other countries to join in limiting use of what would otherwise be economically competitive
fossil fuels; (3) Apply geo-engineering techniques such as stratospheric sulfur injection
to limit global average temperature increase, without a major global reduction in carbon
emissions. Taking into account Chinaâs expected influence and approach to limiting the
impact of anthropogenic climate change allows for a narrower range of possible outcomes
than for a set of scenarios that are not constrained by analysis of likely policy-driven
limitations. While China could hold back on implementing geoengineering given a
remarkable amount of international cooperation on limiting fossil carbon burning, an
outcome where geoengineering is used to delay the perceived need to limit the atmospheric
CO2 concentration may be difficult to avoid
- âŠ