Browsing by Subject "Physics, Atmospheric Science (0608)"
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Item An Investigation of Raman Lidar Aerosol Measurements and their Application to the study of the Aerosol Indirect Effect(2007-11-26) Russo, Felicita; Hoff, Raymond M.; Pavlis, Erricos C.; Physics; Physics, AtmosphericThe problem of the increasing global atmospheric temperature has motivated a large interest in studying the mechanisms that can influence the radiative balance of the planet. Aerosols are responsible for several radiative effects in the atmosphere: an increase of aerosol loading in the atmosphere increases the reflectivity of the atmosphere and has an estimated cooling effect and is called the aerosol direct effect. Another process involving aerosols is the effect that an increase in their concentration in the atmosphere has on the formation of clouds and is called the aerosol indirect effect. In the latest IPCC report, the aerosol indirect effect was estimated to be responsible for a radiative forcing ranging between -0.3 W/m2 to -1.8 W/m2, which can be as large as, but opposite in sign to, the radiative forcing due to greenhouse gases. The main goal of this dissertation is to study the Raman lidar measurements of quantities relevant for the investigation of the aerosol indirect effect and ultimately to apply these measurements to a quantification of the aerosol indirect effect. In particular we explore measurements of the aerosol extinction from both the NASA Goddard Space Flight Center Scanning Raman Lidar (SRL) and the US Department of Energy (DOE) ARM Climate Research Facility Raman Lidar (CARL). An algorithm based on the chi-squared technique to calculate the aerosol extinction, which was introduced first by Whiteman (1999), is here validated using both simulated and experimental data. It has been found as part of this validation that the aerosol extinction uncertainty retrieved with this technique is on average smaller that the uncertainty calculated with the technique traditionally used. This algorithm was then used to assess the performance of the CARL aerosol extinction retrieval for low altitudes. Additionally, since CARL has been upgraded with a channel for measuring Raman liquid water scattering, measurements of cloud liquid water content, droplet radius and droplet number density using this new capability have been studied. Some discrepancies are found between the CARL and AERI measurements of liquid water path and droplet effective radius and they need to be studied in more detail when a larger dataset is available. To study the correlation between aerosol presence and cloud microphysics the calculations of IE, introduced by Feingold as a parameterization of the aerosol indirect effect, has been performed here for the first time using exclusively Raman lidar data. The work shown here is an indication that the combined measurements of aerosol extinction, cloud liquid water content, droplet radius and droplet number density with a Raman lidar represents an interesting new technique for the study of the aerosol indirect effect.Item Improved Refraction Corrections for Satellite Laser Ranging (SLR) by Ray Tracing through Meteorological Data(2007-07-12) Hulley, Glynn Collis; Hoff, Raymond M.; Pavlis, Erricos C.; Physics; Physics, AtmosphericThe most important accuracy-limiting factor for modern space-based geodetic techniques such as Satellite Laser Ranging (SLR), Very Long Baseline Interferometry (VLBI), the Global Positioning System (GPS), and satellite altimetry is the modeling of atmospheric refraction corrections. SLR uses lasers to measure very precise ranges from ground tracking stations to orbiting geodetic satellites with current single-shot accuracies at the sub-centimeter level.Item Investigations of the spatial and temporal resolution of retrievals of atmospheric CO2 from the Atmospheric InfraRed Sounder (AIRS).(2008-02-05) Maddy, Eric; Strow, Lawrence L.; Physics; Physics, AtmosphericAs the dominant anthropogenic greenhouse gas, carbon dioxide (CO2), represents an important component of climate change (IPCC 2007). Owing to burning of fossil fuels and deforestation, atmospheric CO2 concentrations have increased over 110 parts-per-million by volume (ppmv) from 270 ppmv to 380 ppmv since the dawn of the Industrial Revolution. Understanding of the spatial distribution of the sources and sinks of atmospheric CO2 is necessary not only to predict the future atmospheric abundances but also their effect on future climate. Although designed for deriving high precision temperature and moisture profiles, NASA's Atmospheric InfraRed Sounder (AIRS) IR measurements include broad vertical sensitivity (between 3 and 10 km) to atmospheric CO2 variations. Coupled with AIRS' broad swath pattern and a technique referred to as ""cloud-clearing"" these measurements enable daily global spatial coverage. Nevertheless, AIRS' ability to determine the spatial distribution of carbon dioxide (CO2) is strongly dependent on its ability to separate the radiative effects of CO2 from temperature not to mention measurement uncertainties due to clouds and other geophysical variables such as moisture and ozone. This research presents a thorough investigation into the temporal and spatial scales that the AIRS can separate temperature (and other geophysical variables) from CO2. Through our detailed understanding of the way satellites view the Earth's atmosphere, we have developed an algorithm capable of retrieving global middle-to-upper tropospheric CO2 concentrations in all-weather conditions with total uncertainties ranging between 1 to 2 ppmv. From a radiative perspective, roughly equivalent to 30 mK to 60 mK, 1 to 2 ppmv, is an awesome feat for a space-borne sensor. Necessary for the remarkable performance of this algorithm, we developed methodologies capable of separating the radiative effect of CO2 variability from temperature, improved the fast rapid transmittance algorithm for AIRS, and derived algorithm diagnostics that provide the case-dependent skill of AIRS algorithms for temperature and all other constituents (e.g. H2O, O3, CO, CH4, and CO2) from theoretical considerations. As a result, the 1 to 2 ppmv uncertainties match extremely well with simulation; experiments performed before validation experiments had collected data and the retrieval algorithm was still in its infancy.Item Spatio-Temporal Modeling of Rain Rates(2007-11-26) Siddani, Ravi K.; Roy, Anindya; Kundu, Prasun; Mathematics and Statistics; StatisticsModeling episodes of heavy rain is an important component of hydrological studies. Based on the analysis of ship-borne radar data over the tropical ocean, we propose a new class of probability densities that capture the frequency of heavy rain occurrences. This density is constructed by inverting the characteristic function constructed from the moments computed at both integral and fractional orders, for all spatial scales. We demonstrate an improvement over the conventional log-normal distribution at explaining the behavior of intense rain events, and successfully explain the multiscaling characteristics of the rain field. An important assumption in the analysis of space-time characteristics of rain fields is isotropy and homogeneity. We test the equality of spectral densities at multiple locations in a non-parametric setting using the data periodograms. The efficacy of our methodology is demonstrated through simulation, and the theoretical properties of the proposed test statistic are examined. We establish the fact that the test asymptotically maintains the desired level of significance and is consistent at any alternative, and apply our methodology to real life rain rate data set taken from a network of rain gauges in Melbourne, South Florida. This research was supported by a NASA grant under the Precipitations Measurement Missions (PMM) program.Item Temperature Change and Water Vapor Feedback in The Atmosphere. A Comprehensive Assessment Using The Atmospheric InfraRed Sounder Instrument on NASA AQUA Satellite.(2008-01-01) Gambacorta, Antonia; Strow, Larrabee; Physics; Physics, AtmosphericGlobal surface temperature has increased &sim0.2 degree Celsius per decade in the past 30 years [Hansen et al. 2006] . Observational data recorded from 1850 to 2007 indicate that the warmest 11 years have occurred between 1995 and 2006. The 2007 report of the Intergovernmental Panel on Climate Change concluded that there is a very high confidence - 95% confidence - that the global average net effect of human activities since 1750 has been one of warming and that most of the observed increase in global average temperatures since the mid-20th century is very likely - 90% confidence - due to the observed increase in anthropogenic greenhouse gas concentrations. Processes in the climate system that can either amplify or dampen the climate response to an external forcing such as an increase in anthropogenic greenhouse gas concentrations, and directly or indirectly affect the Earth's radiation budget at the top of the atmosphere are normally referred to as climate feedbacks. Among all trace gases, water vapor is the most sensitive to temperature variations. In fact, water vapor absorbs strongly in the vibration-rotation and pure rotation bands at wavelengths in which a large portion of infrared emission occurs at temperature characteristic of the Earth's surface and atmosphere In the present study, we exploit the uniform spatial coverage and high vertical resolution of the Atmospheric InfraRed Sounder database of temperature and water vapor profiles to perform a detailed investigation of the covariance between temperature and water vapor. Unlike previous studies, that only analyzed the overall tropically averaged water vapor and temperature relationship, we make a more comprehensive analysis by investigating this relationship on a local basis. By doing so, we explore the horizontal gradient of this relationship in the tropics, in order to better confine its range of variability and the interplay of the physical processes underneath it. In trying to provide a conclusive assessment on the overall water vapor feedback in the tropical region, correlations between tropically averaged water vapor and temperature are analyzed as well. We observe that the highest and positive correlation values occur in the upper troposphere, where values are seen to approach the thermodynamic equilibrium regime. These results appear to confirm an overall positive water vapor feedback to increased surface temperature in the tropical domain.