Developing a Model for Detailed Simulations of the Chemistry and Aerosol Microphysics of Stratospheric Volcanic Injections With a Focus on Two Case Studies: The June 15th, 1991 Eruption of Mount Pinatubo and the August 12th-15th Eruption of Cerro Hudson

A version of the Goddard Earth Observing System (GEOS) has beendeveloped for simulating dynamics and impacts of volcanic sulfate aerosols in the stratosphere. The GEOS-Chem chemistry module simulates the chemistry of the volcanic plume, using online oxidants and a detailed treatment of both the sulfur cycle and stratospheric ozone. Aerosol microphysics are simulated using the Community Aerosol and Radiation Model for Atmospheres (CARMA) sectional aerosol model. In this thesis, this model is described then applied to the case of stratospheric volcanic aerosols in 1991 from the June 15th Mount Pinatubo (15&deg;N, 120&deg;E) eruption and the August 15th Cerro Hudson (45&deg;S, 72&deg;W) eruption. The model is constrained by observations and applied to scientific questions about volcanic aerosols. The 1991 eruption of Mount Pinatubo injected between 10 Tg and 20 Tg of SO2 gas into the stratosphere, making it the largest volcanic injection of the satellite era. Modeling evidence shows that hydroxyl radical concentrations in the plume may have become depleted by 90% in the days following the eruption, slowing the initial oxidation of SO2. Our model supports this hypothesis, showing the e-folding time for SO2 increasing from a background value of 31 days to more than 200 days. Two months later, Cerro Hudson erupted 2.6 Tg SO2 into the Southern midlatitudes. Modeling studies of Pinatubo have often neglected the Cerro Hudson eruption and attributed Southern Hemisphere observations of stratospheric aerosol in 1991 to transport of Pinatubo aerosols across the equator. The model developed here suggests that half of the optical depth in the Southern Hemisphere stratosphere in 1991 was a result of Cerro Hudson. Observations of volcanic aerosols and anomalously low ozone in the stratosphere above McMurdo Bay (77&deg;S, 166&deg;E) and South Pole Station in September and October 1991 suggest Cerro Hudson aerosols also impacted the 1991 ozone hole. Our model shows that Cerro Hudson may have decreased ozone by 26% between 15 km and 20 km by providing extra surface area for heterogeneous chemistry in September 1991. Additionally, the model shows that the radiative and dynamical impact of Cerro Hudson slowed ozone recovery between 20 km and 25 km.</p

Multi-wavelength study of a new Galactic SNR G332.5-5.6

We present compelling evidence for confirmation of a Galactic supernova remnant (SNR) candidate, G332.5-5.6, based initially on identification of new, filamentary, optical emission line nebulosity seen in the arcsecond resolution images from the AAO/UKST HAlpha survey. The extant radio observations and X-ray data which we have independently re-reduced, together with new optical spectroscopy of the large-scale fragmented nebulosity, confirms the identification. Optical spectra, taken across five different, widely separated nebula regions of the remnant as seen on the HAlpha images, show average ratios of [NII]/HAlpha =2.42, [SII]/HAlpha = 2.10, and [SII] 6717/6731 = 1.23, as well as strong [OI] 6300, 6364A and [OII] 3727A emission. These ratios are firmly within those typical of SNRs. Here, we also present the radio-continuum detection of the SNR at 20/13cm from observations with the Australia Telescope Compact Array (ATCA). Radio emission is also seen at 4850 MHz, in the PMN survey (Griffith and Wright 1993) and at 843 MHz from the SUMSS survey (Bock, Large and Sadler 1999). We estimate an angular diameter of ~30 arcmin and obtain an average radio spectral index of alpha = -0.6 +- 0.1 which indicates the non-thermal nature of G332.5-5.6. Fresh analysis of existing ROSAT X-ray data in the vicinity also confirms the existence of the SNR. The distance to G332.5-5.6 has been independently estimated by Reynoso and Green (2007) as 3.4 kpc based on measurements of the HI lambda21 cm line seen in absorption against the continuum emission. Our cruder estimates via assumptions on the height of the dust layer (3.1 kpc) and using the Sigma-D relation (4 kpc) are in good agreement.Comment: 14 pages, 18 figures. Accepted for publishing in the MNRA

Anisotropy as a Probe of the Galactic Cosmic Ray Propagation and the Galactic Halo Magnetic Field

The anisotropy of cosmic rays (CRs) in the solar vicinity is generally at- tributed to the CR streaming due to the discrete distribution of CR sources or local magnetic field modulation. Recently, the two dimensional large scale CR anisotropy has been measured by many experiments in TeV-PeV energy range in both hemispheres. The tail-in excess along the tangential direction of the local spiral arm and the loss cone deficit pointing to the north Galactic pole direction agree with what have been obtained in tens to hundreds of GeV. The persistence of the two large scale anisotropy structures in such a wide range of energy suggests that the anisotropy might be due to a global streaming of the Galactic CRs (GCRs). This work tries to extend the observed CR anisotropy picture from solar system to the whole galaxy. In such a case, we can find a new interesting signature, a loop of GCR streaming, of the GCR propagation. We further calculate the overall GCR streaming induced magnetic field, and find a qualitative consistence with the observed structure of the halo magnetic field

Strong magnetic fields and cosmic rays in very young galaxies

We present a scenario for efficient magnetization of very young galaxies about 0.5 Gigayears after the Big-Bang by a cosmic ray-driven dynamo. These objects experience a phase of strong star formation during this first $10^9$ years. We transfer the knowledge of the connection between star formation and the production rate of cosmic rays by supernova remnants to such high redshift objects. Since the supernova rate is a direct measure for the production rate of cosmic rays we conclude that very young galaxies must be strong sources of cosmic rays. The key argument of our model is the finding that magnetic fields and cosmic rays are dynamically coupled, i.e. a strong cosmic ray source contains strong magnetic fields since the relativistic particles drive an efficient dynamo in a galaxy via their buoyancy. We construct a phenomenological model of a dynamo driven by buoyancy of cosmic rays and show that if azimuthal shearing is strong enough the dynamo amplification timescale is close to the buoyancy timescale of the order of several $10^7 \div 10^8$ yr. We predict that young galaxies are strongly magnetized and may contribute significantly to the gamma-ray-background.Comment: 9 pages, 1 figure, accepted for Astronomy and Astrophysic

Can Conditional Cash Transfers compensate for a father’s absence?

This paper investigates how the departure of the father from the household, that results in his permanent absence, affects children’s school enrollment and work participation in rural Colombia. The results show that departure of the father decreases children’s school enrollment by around 5 percentage points and increases child labor by 3 percentage points. The paper exploits the roll-out of a conditional cash transfer program during the period of study and shows that it counteracts these adverse effects. This, and other pieces of evidence provided, strongly suggests that the channel through which the father’s departure affects children is through reducing the income of very poor households, which is tightening their liquidity constraints. It also highlights the important safety net role played by such welfare programs, in particular for disadvantaged households, which are unlikely to find formal or informal ways of insuring themselves against such vagaries