A new theory for tropical instability waves

Large-scale westward propagating waves, so-called "Legeckis" or "Tropical Instabil- ity Waves", are a prominent feature of sea surface temperature images of the equatorial Pacific. Our analyses of satellite altimetry data and long-term moorings reveals that the Legeckis waves can be interpreted as a superposition of two distinct wave modes, a first equatorial Rossby wave and a Rossby-gravity wave. We present evidence that the energy sources for both waves are the mean currents. Our results imply that Legeckis waves can be explained within the framework of linear equatorial waves

Assessing inflow rates in atomic cooling halos: implications for direct collapse black holes

Supermassive black holes are not only common in the present-day galaxies, but billion solar masses black holes also powered $z\geq 6$ quasars. One efficient way to form such black holes is the collapse of a massive primordial gas cloud into a so-called direct collapse black hole. The main requirement for this scenario is the presence of large accretion rates of $\rm \geq 0.1~M_{\odot}/yr$ to form a supermassive star. It is not yet clear how and under what conditions such accretion rates can be obtained. The prime aim of this work is to determine the mass accretion rates under non-isothermal collapse conditions. We perform high resolution cosmological simulations for three primordial halos of a few times $\rm 10^7~M_{\odot}$ illuminated by an external UV flux, $\rm J_{21}=100-1000$. We find that a rotationally supported structure of about parsec size is assembled, with an aspect ratio between $\rm 0.25 - 1$ depending upon the thermodynamical properties. Rotational support, however, does not halt collapse, and mass inflow rates of $\rm \sim 0.1~M_{\odot}/yr$ can be obtained in the presence of even a moderate UV background flux of strength $\rm J_{21} \geq 100$. To assess whether such large accretion rates can be maintained over longer time scales, we employed sink particles, confirming the persistence of accretion rates of $\rm \sim 0.1~M_{\odot}/yr$. We propose that complete isothermal collapse and molecular hydrogen suppression may not always be necessary to form supermassive stars, precursors of black hole seeds. Sufficiently high inflow rates can be obtained for UV flux $\rm J_{21}=500-1000$, at least for some cases. This value brings the estimate of the abundance of direct collapse black hole seeds closer to that high redshift quasars.Comment: Accepted for publication in MNRAS, comments are still welcom

Generation of SST anomalies in the midlatitudes

Analyses of monthly mean sea surface temperatures (SST) from a hierarchy of global cou- pled ocean-atmosphere models have been carried out with the focus on the midlatitudes (20N-45N). The spectra of the simulated SSTs have been tested against the null hypothe- sis of Hasselmann's stochastic climate model, which assumes an AR(1)-process for the SST variability. It has been found that the spectra of the SST variability in CGCl\/ls with fully dynamical ocean models are significantly different from the AR(1)-process, while the SST variability in an AGCM coupled to a slab ocean is consistent with an AR(1)-process. The deviation of the SST variability in CGCl\/ls with fully dynamical ocean models from the AR(1)-process are not characterized by spectral peaks but are due to a different shape of the spectra. This can be attributed to local air-sea interactions which can be simulated with an AGCM coupled to a slab ocean with dynamical varying mixed layer depth

The formation of supermassive black holes in rapidly rotating disks

Massive primordial halos exposed to moderate UV backgrounds are the potential birthplaces of supermassive black holes. In such a halo, an initially isothermal collapse will occur, leading to high accretion rates of $\sim0.1$~M$_\odot$~yr$^{-1}$. During the collapse, the gas in the interior will turn into a molecular state, and form an accretion disk due to the conservation of angular momentum. We consider here the structure of such an accretion disk and the role of viscous heating in the presence of high accretion rates for a central star of $10$, $100$ and $10^4$~M$_\odot$. Our results show that the temperature in the disk increases considerably due to viscous heating, leading to a transition from the molecular to the atomic cooling phase. We found that the atomic cooling regime may extend out to several $100$~AU for a $10^4$~M$_\odot$ central star and provides substantial support to stabilize the disk. It therefore favors the formation of a massive central object. The comparison of clump migration and contraction time scales shows that stellar feedback from these clumps may occur during the later stages of the evolution. Overall, viscous heating provides an important pathway to obtain an atomic gas phase within the center of the halo, and helps in the formation of very massive objects. The latter may collapse to form a massive black hole of about $\geq 10^4$~M$_\odot$.Comment: Accepted for publication in Astronomy & Astrophysics, comments are still welcom

Biodegradation of rocket propellant waste, ammonium perchlorate

The short term effects of ammonium perchlorate on selected organisms were studied. A long term experiment was also designed to assess the changes incurred by ammonium perchlorate on the nitrogen and chloride contents of soil within a period of 3 years. In addition, an attempt was made to produce methane gas from anaerobic fermentation of the aquatic weed, Alternanthera philoxeroides