This thesis develops several unique different precipitation statistics and verification measures that are applicable to scales relevant to global climate models, regional models and hydrological runoff models, through a series of three papers.The first section of the dissertation is motivated by the fact that climate models are unable to account for the variability of precipitation within a grid box, and that other hydrologically critical precipitation characteristics, such as intensity and frequency, are often times overlooked in the literature. Several issues related to spatial averaging of these two measures are investigated. Rain gauge reports and radar precipitation analyses are used here to address three issues related to the areal estimation of intensity and frequency of precipitation. Differences between the order of spatial and temporal averaging methods are proven to be significant; therefore quantifying these differences is critical for both climate model diagnostics and downscaling applications.The second section documents spatio-temporal statistics of hourly fine-scale precipitation analyses for the continental U.S. The spatio-temporal coherence of precipitation fields, quantified under the assumption of isotropy, reveals significant seasonal and geographical variations. Anisotropic factors are then considered to obtain estimates of the mean movement and orientation of the precipitating storm systems.The dissertation provides new methodology to quantify the spatio-temporal variability of observed and modeled precipitation that offers new insight into how to correct erroneous model simulations.The methodologies are used to evaluate the performance of two mesoscale atmospheric forecast models, one with explicit treatment of convection and the other with a convective parameterization scheme. Designed to account for the transient and intermittent character of precipitation, these new verification techniques show that explicit formulation of convection yields spatio-temporal covariance structures that agree closely with observations. The explicit scheme shows however, a systematic tendency to propagate summertime precipitating storm systems to the right of observations, suggesting that the model's convection is too dependent on the source of low-level moisture.

Limited Time Period (LTP) running trends are used to evaluate Microwave Sounding Unit (MSU) derived tropospheric temperature trend methods in an attempt to alleviate documented considerable disagreements between tropospheric datasets so investigation into the atmospheric variability is able to move forward.Regression derived coefficients were used to combine lower stratosphere (LS) and mid-troposphere to lower stratosphere (MT) simulated MSU channels from RATPAC radiosonde data. This protocol is used to estimate tropospheric temperature trends and compared to actual RATPAC derived tropospheric temperature trends. It is found that the statistical LS/MT combination results in greater than 50% error over some LTP. These errors are found to exist when strong cooling in the stratosphere is coincident with periods when the level separating cooling from warming is above the tropopause.LTP trends are also created from various MSU difference time series between the University of Alabama in Huntsville (UAH) and Remote Sensing System (RSS) group's lower troposphere (LT) and MT channels. Results suggest the greatest discrepancies over time periods where NOAA-11 through NOAA-15 adjustments was applied to the raw LT data over land. Discrepancies are shown to be dominated by differences in diurnal correction methods due to orbital drift. Comparison of MSU data with radiosonde data indicate that RSS's method of determining diurnal effects is overestimating the correction in the LT channel. Diurnal correction signatures still exist in the RSS LT time series and are likely affecting the long term trend with a warm bias.These findings suggest atmospheric amplification is not happening in the atmosphere using globally averaged data over the MSU era. There is evidence however from the radiosonde data that shows greater warming in the ~300-500 hPa layer than at the surface during some LTP in the complete radiosonde database. This temporal change in temperature trends warrants further studies on this subject.This research suggests overall that the temporal changes in temperature trend profiles and their causes are extremely important in our understanding of atmospheric changes and are themselves, not well characterized.

<p> Mineral dust aerosols can impact air quality, climate change, biological cycles, tropical cyclone development and flight operations due to reduced visibility. Dust emissions are primarily limited to the extensive arid regions of the world, yet can negatively impact local to global scales, and are extremely complex to model accurately. Within this dissertation, the Dust Entrainment And Deposition (DEAD) model was adapted to run, for the first known time, using high temporal (hourly) and spatial (0.3&deg;x0.3&deg;) resolution data to methodically interrogate the key parameters and factors influencing global dust emissions. The dependence of dust emissions on key parameters under various conditions has been quantified and it has been shown that dust emissions within DEAD are largely determined by wind speeds, vegetation extent, soil moisture and topographic depressions. Important findings were that grid degradation from 0.3&ordm;x0.3&ordm; to 1&ordm;x1&ordm;, 2&ordm;x2.5&ordm;, and 4&deg;x5&deg; of key meteorological, soil, and surface input parameters greatly reduced emissions approximately 13% and 29% and 64% respectively, as a result of the loss of sub grid detail within these key parameters at coarse grids. After running high resolution DEAD emissions globally for 2 years, two severe dust emission cases were chosen for an in-depth investigation of the root causes of the events and evaluation of the 2&deg;x2.5&deg; Goddard Earth Observing System (GEOS)-Chem and 0.3&deg;x0.3&deg; DEAD model capabilities to simulate the events: one over South West Asia (SWA) in June 2008 and the other over the Middle East in July 2009. The 2 year lack of rain over SWA preceding June 2008 with a 43% decrease in mean rainfall, yielded less than normal plant growth, a 28% increase in Aerosol Optical Depth (AOD), and a 24% decrease in Meteorological Aerodrome Report (METAR) observed visibility (VSBY) compared to average years. GEOS-Chem captured the observed higher AOD over SWA in June 2008. More detailed comparisons of GEOS-Chem predicted AOD and visibility over SWA with those observed at surface stations and from satellites revealed overall success of the model, although substantial regional differences exist. Within the extended drought, the study area was zoomed into the Middle East (ME) for July 2009 where multi-grid DEAD dust emissions using hourly CFSR meteorological input were compared with observations. The high resolution input yielded the best spatial and temporal dust patterns compared with Defense Meteorological Satellite Program (DMSP), Moderate Resolution Imaging Spectroradiometer (MODIS) and METAR VSBY observations and definitively revealed Syria as a major dust source for the region. The coarse resolution dust emissions degraded or missed daily dust emissions entirely. This readily showed that the spatial scale degradation of the input data can significantly impair DEAD dust emissions and offers a strong argument for adapting higher resolution dust emission schemes into future global models for improvements of dust simulations.</p>

<p> Smoke plumes associated with wildland fires are difficult to characterize due to the non-linear behavior of the variables involved. Plume chemistry is largely modeled using emission factors to represent the relative trace gas and aerosol species emitted. Plume dynamics are modeled based on assumptions of plume vertical distribution and atmospheric dispersion. In the studies presented here, near and in-source measurements of emissions from prescribed burns are used to characterize the variability of emission factors from low-intensity fires. Emissions factors were found to be in the same range as those from other, similar studies in the literature and it appears that the emission factors may be sensitive to small differences in surface conditions such as fuel moisture, surface wind speed, and the ratio of live to dead fuels. We also used two coupled fire atmosphere models, which utilize the Weather Research and Forecasting (WRF) model called WRF-Fire and WRF-Sfire, to investigate the role that atmospheric stability plays in influencing plume rise as well as developing a technique for assessing plume rise and the vertical distribution of pollutants in regional air quality models. Plume heights, as well as rate of growth of the fire, were found to be sensitive to atmospheric stability while fire rate of spread was not. The plume center-of-mass technique was demonstrated to work well but has slightly low estimates compared to observations. </p>

Considerable research has been performed on persistent-anomaly structures for the Northern Hemisphere winter. However, atmospheric blocking structures during the warm season also have a considerable impact on weather and climate, as manifested through heat waves, floods, and droughts. In particular, atmospheric blocked flow has a profound impact on anomalously-dry regimes over the central North American continent. In order to provide a better understanding of the life cycle of the atmospheric blocking events and their relation to fast-climate phenomena, we analyse persistent height-anomaly structures derived from the National Centers for Environmental Prediction (NCEP) global reanalyses. We devise an objective criterion for the characterization of blocked flow by relating it to persistent positive height anomalies. Individual warm-season events over the North American continent are then identified and examined in case studies. This reveals a type of blocking regime, differing in structure from the Rex and Omega type blocks described in the literature, as being important in the region during summer. Moreover, changes in the statistical distribution of the event frequencies are analysed in order to detect climatic trends. We find a pronounced westward displacement of the North American anomaly event frequency maximum to be associated with the 1999-2004 drought in the Canadian Prairies.

<p> The upper troposphere lower stratosphere (UTLS) is a region of minimum temperatures that contains the tropopause. As a transition region between the troposphere and the stratosphere, the UTLS contains various processes that facilitate stratosphere-troposphere exchange (STE) which can redistribute radiatively important species such as water vapor or ozone. One potential marker for STE is the double tropopause (DT). Therefore this study seeks to further understand how DTs form and how they could enhance the current understanding of some STE processes in the UTLS. </p><p> Using data from the High Resolution Dynamic Limb Sounder (HIRDLS), a data set with high vertical and horizontal resolution, newly discovered DT structures are found over the Pacific and Atlantic oceans that suggest a relationship between the DT and both storm tracks and Rossby waves. The association between DTs and storm tracks is examined by further analyzing the recently discovered and unexpected relationship between the DT and the tropopause inversion layer (TIL) in a developing baroclinic disturbance. Results show an increase in the number of DTs when the lapse rate of the extratropical TIL is less than -2&deg;C/km, i.e. when the TIL is stronger and the local stability is higher. Composites of ERA-Interim DT profiles for three different TIL strengths shows that the vertical motion and relative vorticity both decrease as the TIL increases, which suggests the warm conveyor belt as a mechanism. This is investigated further with a case study analysis of a developing extratropical cyclone in the Pacific Ocean. Additionally, an analysis of DTs in relation to the large scale flow responsible for storm development shows a strong correlation between monthly Rossby wave activity, ozone laminae and DT variability. Further examination shows that if these waves break a DT will be found with a wave breaking event about 30% of the time in the eastern Pacific and eastern Atlantic oceans, both regions of poleward wave breaking. </p><p> These results highlight a new and more complicated DT structure that is a product of both large scale dynamics and small scale vertical motions, thus adding new information to the current understanding of the UTLS.</p>

<p> Downdrafts are an integral part of the convective cycle, and have been observed and documented for more than a hundred years. But many questions still surround convective downdrafts and their most difficult to observe properties. These questions have made the parameterization of convective downdrafts in global climate models (GCMs) very difficult. Designers of parameterizations have resorted to a wide range of assumptions and unverified hypotheses in their models of convective downdrafts. </p><p> In the last ten years, computing resources have advanced to a point where large domain, high resolution cloud resolving models (CRMs) can easily be run for long simulations. This study uses several simulations with 1 km horizontal resolution from the System for Atmospheric Modeling (SAM) v6.8.2 to examine convective downdrafts. We look at Radiative-Convective Equilibrium (RCE), a 21 day case from TOGA-COARE, Weak Temperature Gradient (WTG) simulations with varied shear profiles, and Lagrangian Parcel data to consider many difficult to observe properties of downdrafts. </p><p> We consider a variety of assumptions and questions that arise in the development of convective parameterizations. Our results show that downdrafts are an important mass flux in all simulations, and that cold pools organize convective systems and enhance updraft Convective Available Potential Energy (CAPE). We examine the ability for downdrafts to help couple deep convection to high relative-humidity regions in the tropics, and find that entrainment is likely a more important process in this relationship. We discuss the impact of downdrafts in maintaining boundary layer quasi-equilibrium, and find that, in our simulations, environmental entrainment has a larger impact on low-level most static energy. Finally, we show results from Lagrangian parcel data that illuminate our downdrafts as existing in an unsaturated state, with increasing buoyancy as they descend. We show that many of our downdrafts have positive buoyancy perturbations, suggesting the presence of warm downdrafts and under-shooting bottoms in heavily precipitating tropical systems.</p>

<p> Aerosols and clouds play important roles in the climate system through their radiative effects and their vital link in the hydrological cycle. Accurate measurements of aerosol and cloud optical and microphysical properties are crucial for the study of climate and climate change. This study develops/improves retrieval algorithms for aerosol single scattering albedo (SSA) and low liquid water path (LWP) cloud optical properties, evaluates a new spectrometer, and applies long-term measurements to establish climatology of aerosol and cloud optical properties. The following results were obtained. </p><p> (1) The ratio of diffuse horizontal and direct normal fluxes measured from Multifilter Rotating Shadowband Radiometer (MFRSR) has been used to derive the aerosol SSA. Various issues have impacts on the accuracy of SSA retrieval, from measurements (e.g., calibration accuracy, cosine respond correction, and forward scattering correction) to input parameters and assumptions (e.g., asymmetry factor, Rayleigh scattering optical depth, and surface albedo). This study carefully analyzed these issues and extensively assessed their impacts on the retrieval accuracy. Furthermore, the retrievals of aerosol SSA from MFRSR are compared with independent measurements from co-located instruments. </p><p> (2) The Thin-Cloud Rotating Shadowband Radiometer (TCRSR) has been used to derive simultaneously the cloud optical depth (COD) and cloud drop effective radius (DER), subsequently inferring the cloud liquid-water path (LWP). The evaluation of the TCRSR indicates that the error of radiometric calibration has limited impact on the cloud DER retrievals. However, the retrieval accuracy of cloud DER is sensitive to the uncertainties of background setting (e.g., aerosol loading and the existence of ice cloud) and the measured solar aureole shape. </p><p> (3) A new high resolution oxygen A-band spectrometer (HABS) has been developed, which has the ability to measure both direct-beam and zenith diffuse solar radiation with polarization capability. The HABS exhibits excellent performance: stable spectral response ratio, high SNR, high spectrum resolution (0.16 nm), and high Out-of-Band Rejection (10^-5). The HABS measured spectra and polarization spectra are basically consistent with the related simulated spectra. The main difference between them occurs at or near the strong oxygen absorption line centers. Furthermore, our study demonstrates that it is a good method to derive the degree of polarization-oxygen absorption optical depth (DOP-k) relationship through a polynomial fitting in the DOP-k space. </p><p> (4) The long-term MFRSR measurements at Darwin (Australia), Nauru (Nauru), and Manus (Papua New Guinea) sites have been processed to develop the climatology of aerosols and clouds in the Tropical Warm Pool (TWP) region at the interannual, seasonal, and diurnal temporal scales. Due to the association of these three sites with large-scale circulation patterns, aerosol and cloud properties exhibit distinctive characteristics. The cloud optical depth (COD) and cloud fraction (CF) exhibit apparent increasing trends from 1998 to 2007 and decreasing trends after 2007. The monthly anomaly values, to some extent, are bifurcately correlated with SOI, depending on the phase of ENSO. At the two oceanic sites of Manus and Nauru, aerosols, clouds, and precipitation are modulated by the meteorological changes associated with MJO events. </p><p> (5) The long-term measurements at Barrow and Atqasuk sites also have been processed to develop the climatology of aerosol and cloud properties in the North Slope of Alaska (NSA) region at interannual, seasonal, and diurnal temporal scales. Due to Arctic climate warming, at these two sites, the snow melting day arrives earlier and the non-snow-cover duration increases. Aerosol optical depth (AOD) increased during the periods of 2001-2003 and 2005-2009, and decreased during 2003-2005. The LWP, COD, and CF exhibit apparently decreasing trends from 2002 to 2007 and increased significantly after 2008. (Abstract shortened by UMI.)</p>

No description available.

No description available.