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Buitrago-Casas J.C.,University of California at Berkeley | Buitrago-Casas J.C.,National University of Colombia | Martinez Oliveros J.C.,University of California at Berkeley | Lindsey C.,Colorado Research Associates Division | And 6 more authors.
Solar Physics | Year: 2015

Several mechanisms have been proposed to explain the transient seismic emission, i.e. “sunquakes,” from some solar flares. Some theories associate high-energy electrons and/or white-light emission with sunquakes. High-energy charged particles and their subsequent heating of the photosphere and/or chromosphere could induce acoustic waves in the solar interior. We carried out a correlative study of solar flares with emission in hard X-rays, enhanced continuum emission at 6173 Å, and transient seismic emission. We selected those flares observed by the Reuven Ramaty High Energy Solar Spectroscopic Imager (RHESSI) with a considerable flux above 50 keV between 1 January 2010 and 26 June 2014. We then used data from the Helioseismic and Magnetic Imager onboard the Solar Dynamic Observatory to search for excess visible-continuum emission and new sunquakes not previously reported. We found a total of 18 sunquakes out of 75 flares investigated. All of the sunquakes were associated with an enhancement of the visible continuum during the flare. Finally, we calculated a coefficient of correlation for a set of dichotomic variables related to these observations. We found a strong correlation between two of the standard helioseismic detection techniques, and between sunquakes and visible-continuum enhancements. We discuss the phenomenological connectivity between these physical quantities and the observational difficulties of detecting seismic signals and excess continuum radiation. © 2015, Springer Science+Business Media Dordrecht. Source


Brown J.,Colorado Research Associates Division | Fiechter J.,University of California at Santa Cruz
Dynamics of Atmospheres and Oceans | Year: 2012

Many analyses of the interaction between ocean physics and biology in the Coastal Gulf of Alaska (CGOA) resolve chlorophyll variability separately from eddy-induced circulation, but eddy-chlorophyll covariability has not received much attention. The present research quantified eddy-chlorophyll interaction from the covariability of observed chlorophyll and eddy kinetic energy (EKE) in the CGOA for 1998-2002. Analyses with coupled empirical orthogonal functions (CoEOFs) showed that covariability between the two fields resulted in strongly coupled modes-a feature absent from standard-EOF analyses. Timescales of covariability were also incorporated into the analyses. The temporal evolution of each CoEOF mode was decomposed with the cross-wavelet power spectrum, and instances of covariability for synoptic timescales (2-6 months) were attributed to eddy-chlorophyll interaction. Further analyses in the present research included CoEOF decomposition for the output of a coupled physical-biological model in the CGOA. Model-observation comparisons with CoEOFs offer a new and important way to evaluate coupled models for eddy-chlorophyll interaction across multiple temporal and spatial scales. Implications for cross-shelf transport and spatiotemporal sampling for both observation and model data fields are also discussed. © 2012 Elsevier B.V.. Source


Ortland D.A.,NorthWest Research Associates, Inc. | Alexander J.M.,Colorado Research Associates Division
Journal of the Atmospheric Sciences | Year: 2011

Observation and modeling studies indicate that the wave flux from tropical heating sources that propagates into the lower stratosphere is sensitive to the buoyancy frequency profile N(z) in the troposphere. This sensitivity is explained by examining analytic solutions to the vertical structure equation for various simplified models of the tropical troposphere. An efficient method for obtaining expressions for these analytic solutions when N(z) is piecewise constant is presented. The solution is expressed in terms of reflection and transmission coefficients. It is found that the response to heating for Hough modes with small equivalent depth is quite sensitive to the shape of the heating profile, the magnitude of N(z) within the heating profile, and the internal wave reflections that result from the sharp change in N(z) at the tropopause. The location of the primary peak in the wave response, which occurs where the wavelength is twice the depth of the heating for a constant N(z) profile, is also sensitive to the occurrence of internal wave reflection. © 2011 American Meteorological Society. Source


Ryu J.-H.,University of Colorado at Boulder | Ryu J.-H.,Colorado Research Associates Division | Alexander M.J.,University of Colorado at Boulder | Alexander M.J.,Colorado Research Associates Division | Ortland D.A.,NorthWest Research Associates, Inc.
Journal of the Atmospheric Sciences | Year: 2011

Equatorial atmospheric waves in the upper troposphere and lower stratosphere (UTLS), excited by latent heating, are investigated by using a global spectral model. The latent heating profiles are derived from the 3-hourly Tropical Rainfall Measuring Mission (TRMM) rain rates, which include both convective- and stratiform-type profiles. The type of heating profile is determined based on an intensity of the surface rain rate. Latent heating profiles over stratiform rain regions, estimated from the TRMM Precipitation Radar (PR) product, are applied to derive the stratiform-type latent heating profiles from the gridded rain rate data. Monthly zonal-mean latent heating profiles derived from the rain rates appear to be reasonably comparable with the TRMM convective/stratiform heating product. A broad spectrum of Kelvin, mixed Rossby-gravity (MRG), equatorial Rossby (ER), and inertia-gravity waves are generated in the model. Particularly, equatorial waves (Kelvin, ER, and MRG waves) of zonal wavenumbers 1-5 appear to be dominant in the UTLS. In the wavenumber-frequency domain, the equatorial waves have prominent spectral peaks in the range of 12-200 m of the equivalent depth, while the spectral peaks of the equatorial waves having shallower equivalent depth (<50 m) increase in the case where stratiform-type heating is included. These results imply that the stratiform-type heating might be relevant for the shallower equivalent depth of the observed convectively coupled equatorial waves. The horizontal and vertical structures of the simulated equatorial waves (Kelvin, ER, andMRGwaves) are in a good agreement with the equatorial wave theory and observed wave structure. In particular, comparisons of the simulated Kelvin waves and the High Resolution Dynamics Limb Sounder (HIRDLS) satellite observation are discussed. © 2011 American Meteorological Society. Source


Webster P.J.,Georgia Institute of Technology | Jian J.,Georgia Institute of Technology | Hopson T.M.,U.S. National Center for Atmospheric Research | Hoyos C.D.,Georgia Institute of Technology | And 6 more authors.
Bulletin of the American Meteorological Society | Year: 2010

Climate Forecast Applications in Bangladesh (CFAB) decided to issue probabilistic forecasts to support risk management that allowed cost-benefit analyzes to be made relative to the probability of the occurrence of flood. It envisioned a seamless probabilistic prediction system ranging from daily to seasonal forecasts. The principal aim of CFAB was to assess the feasibility of developing a forecast system and, if possible, to develop an operational system to produce such forecasts and identify a means of disseminating these forecasts to user communities. The system has been shown to work well in two large river basins, Ganga and the Brahmaputra, and is perhaps best suited for river systems that are large monsoonal river basins. Discharge forecasts in the Ganges and Brahmaputra basins could be improved immediately if streamflow data were freely distributed even within India itself. Better developmental and funding models are needed to provide aid to developing economies for the provision of relevant decision-oriented information. Source

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