ALBERT

Description: The solar cycle (SC) effect in the lower atmosphere has been linked observationally to the Quasi-biennial Oscillation (QBO), which is generated primarily by small-scale gravity waves (GW). Following up on a 2D study with our Numerical Spectral Model (NSM), we discuss here a 3D study in which we simulated the QBO under the influence of the SC. For a SC period of 10 years, the relative amplitude of radiative forcing is taken to vary exponentially with height, i.e., 0.2% at the surface, 2% at 50 km, 20% at 100 km and above. Applying spectral analysis to filter out and identify the SC signature, this model produces a relatively large modulation in the QBO of the lower stratospheric circulation, which is in qualitative agreement with the results obtained by Salby and Callaghan (2000) who analyzed zonal wind observations covering more than 40 years. The modeled SC modulation of the QBO extends to high latitudes where it produces temperature variations of about 1 K in the troposphere below 10 km. We report that the SC also generates in the model a hemispherically symmetric Equatorial Annual Oscillation (EAO, with 12-month period) that is largely confined to low latitudes. Under the influence of the GWs, the SC modulated EA0 propagates down into the lower stratosphere like the QBO. As is the case for the QBO, the energy of this EA0 is partially redistributed by the meridional circulation and planetary waves, presumably, to generate measurable SC signatures in the tropospheric temperature of the polar regions, which may be related to the so called Arctic Oscillation (Thompson and Wallace, 1998). The larger SC influence at higher altitudes is apparently transferred to the lower and denser regions of the atmosphere by tapping the momentum from the upward propagating GWs that drive the oscillations. The SC modulation of the QBO period could prove to be very effective in this process, as our earlier 2D study indicated. Further studies are needed, (1) to make sure that the SC effects are real and the numerical results are robust, and (2) to explore more fully the mechanism(s) that may conspire to amplify the SC effect. Quasi-decadal oscillations, generated internally by the QBO interacting with the seasonal cycles, may interfere with, or aid, the SC influence.

Description: Brown dwarfs are stellar objects with masses less than 0.08 times that of the Sun that are unable to sustain nuclear fusion. Because of the lack of fusion, they are relatively cold, allowing the formation of methane and water molecules in their atmospheres. Brown dwarfs can be detected by examining stars' absorption spectra in the near-infrared to see whether methane and water are present. The objective of this research is to determine the locations of brown dwarfs in Rho Ophiuchus, a star cluster that is only 1 million years old. The cluster was observed in four filters in the near-infrared range using the Wide-Field Infra-Red Camera (WIRC) on the 100" DuPont Telescope and Persson's Auxiliary Nasymith Infrared Camera (PANIC) on the 6.5-m Magellan Telescope. By comparing the magnitude of a star in each of the four filters, an absorption spectrum can be formed. This project uses standard astronomical techniques to reduce raw frames into final images and perform photometry on them to obtain publishable data. Once this is done, it will be possible to determine the locations and magnitudes of brown dwarfs within the cluster.