Open Access. Powered by Scholars. Published by Universities.®
Articles 1 - 30 of 30
Full-Text Articles in Atmospheric Sciences
A Mechanism For Upscale Growth Of Convection In The Complex Terrain Of The Northeast U.S, Brennan Joseph Stutsrim
A Mechanism For Upscale Growth Of Convection In The Complex Terrain Of The Northeast U.S, Brennan Joseph Stutsrim
Legacy Theses & Dissertations (2009 - 2024)
Upstate New York has a variety of complex terrain that can interact with the background flow to create mesoscale heterogeneities in the lower troposphere. The major valleys of Upstate New York, the Hudson and Mohawk Valleys, often have increased moisture content and stronger surface winds than the higher terrain surrounding them. These features can have a profound effect on the evolution of convective storms, especially in cases characterized by low-to-moderate shear, which tends to favor pulse-like or multicellular convection. Analysis of composite radar imagery has indicated that convective storms often change mode while descending from the Catskills Mountains into the …
The Sensitivity Of Convection To Boundary Layer Parameterization In Hurricanes Harvey And Irma 2017, Dylan Card
The Sensitivity Of Convection To Boundary Layer Parameterization In Hurricanes Harvey And Irma 2017, Dylan Card
Legacy Theses & Dissertations (2009 - 2024)
Tropical cyclones (TCs) pose a significant threat to life and property, and exhibit many severe weather hazards as they make landfall, such as storm surge, strong winds, flooding rains, and tornadoes. TC convection is associated with nearly all of these hazards, which can extend hundreds of kilometers inland; thus, understanding the characteristics and organization of convective cells is important to mitigating risk. Observational studies have noted that TC convection tends to organize downshear and that rotating thunderstorms tend to occur in the downshear-right quadrant of the TC. Modeling studies have also shown that convective cells tend to form upshear right …
Factors Influencing Rainfall Over The Congo, Ajay Raghavendra
Factors Influencing Rainfall Over The Congo, Ajay Raghavendra
Legacy Theses & Dissertations (2009 - 2024)
The hydrological cycle over tropical rainforests includes some of the most intense thunderstorms and rainfall totals. The energy associated with this convective activity plays an important role in the Earth’s weather and climate system. Therefore, the interannual variability, trends, and future climate projections of the hydrological cycle over tropical rainforests are important topics for research. The Congo rainforest situated over equatorial Africa is the second largest rainforest in the world, and recent studies have documented a >30-year large-scale and long-term drying trend over the Congo since the late-1970s. However, unlike the Amazon rainforest in South America, the Congo rainforest is …
Evaluating Large-Scale And Storm-Scale Characteristics Of Rapidly Intensifying And Slowly Intensifying Tropical Cyclones Using An Analog Approach, Jannetta C. Richardson
Evaluating Large-Scale And Storm-Scale Characteristics Of Rapidly Intensifying And Slowly Intensifying Tropical Cyclones Using An Analog Approach, Jannetta C. Richardson
Legacy Theses & Dissertations (2009 - 2024)
Tropical cyclone (TC) intensity change is modulated by a combination of large-scale and storm-scale processes. On the large-scale, several factors exhibit strong controls on TC rapid intensification (RI): the initial TC intensity, the environmental vertical wind shear (VWS), and the background thermodynamic environment, which determines the TC’s maximum potential intensity (MPI). Previous statistical studies comparing RI and non-RI TCs have shown that TCs undergoing RI tend to be embedded in environments of lower VWS, and have initial intensities that are farther from their MPIs. Although numerous statistical studies have compared the large-scale and storm-scale conditions of RI and non-RI TCs, …
Easterly Waves Over The Eastern Pacific, Victor Manuel Torres Puente
Easterly Waves Over The Eastern Pacific, Victor Manuel Torres Puente
Legacy Theses & Dissertations (2009 - 2024)
The research in this thesis explores different processes associated with the life cycle of Easterly Waves over the tropical Eastern Pacific. These include genesis, structural evolution, intensification and a dissipating stage.
The Significance Of The Nontraditional Coriolis Terms In Tropical Large-Scale Dynamics, Heng Wang
The Significance Of The Nontraditional Coriolis Terms In Tropical Large-Scale Dynamics, Heng Wang
Legacy Theses & Dissertations (2009 - 2024)
The nontraditional Coriolis terms (NCTs) turn eastward motion upward and upward motion westward, and vice versa. NCTs are omitted in most of the current global atmospheric models. However, NCTs are significant in tropical large-scale dynamics in at least three aspects. 1) Using an idealized model that can switch NCTs on or off, omitting NCTs biases large-scale flow response to prescribed diabatic forcing mimicking the intertropical convergence zone (ITCZ). The omission yields a westerly wind bias in the heating region ~ 10% of the westerly jet stream. This bias is due to lack of westward NCT when heating-induced upward motion is …
A Multiscale Analysis Of The Rainband And Cellular Structure In Hurricanes Harvey And Irma (2017) Using The Ncar Ensemble, Dylan Card
Legacy Theses & Dissertations (2009 - 2024)
Tropical cyclones pose a significant threat to life and property, and exhibit many severe weather hazards as they make landfall, such as storm surge, strong winds, flooding rains, and tornadoes. Tropical cyclone rainbands are associated with nearly all of these hazards, which can extend hundreds of kilometers inland. Thus, understanding tropical cyclone rainband structure, and the individual convective cells of which rainbands are composed, is important to mitigating risk. Several previous studies have documented the overall structure of tropical cyclone rainbands, including the cells of which they are comprised and the environments in which they are embedded. These studies have …
Variability Of African Easterly Waves, Yuan-Ming Cheng
Variability Of African Easterly Waves, Yuan-Ming Cheng
Legacy Theses & Dissertations (2009 - 2024)
African Easterly Waves (AEWs) are the most important rain modulators in the sub-Saharan Africa and precursors for tropical cyclone genesis in the Atlantic. While most previous studies have focused on the mean structure and dynamics of AEWs, evidence has shown that AEWs can vary substantially in terms of their structure and characteristics. Therefore, the overarching goal of this dissertation is to document the variability of AEWs and understand its causes. The goal is accomplished through two different but complementary approaches: (1) statistical analysis and (2) vorticity tracking.
Extratropical Precursors To The Onset Of Madden-Julian Oscillation Deep Convection Over The Western Indian Ocean, Jennifer Anne Gahtan
Extratropical Precursors To The Onset Of Madden-Julian Oscillation Deep Convection Over The Western Indian Ocean, Jennifer Anne Gahtan
Legacy Theses & Dissertations (2009 - 2024)
Madden-Julian Oscillation (MJO) deep convection often initially forms over the western Indian Ocean and is frequently preceded by upper tropospheric circulation precursors. These precursors include subtropical cyclonic Rossby gyres near eastern Africa and Southwest Asia, coherent extratropically circumnavigating Rossby wave trains extending back across the Atlantic, and tropically circumnavigating easterlies. Easterly acceleration associated with the circulation precursors may help to reduce large-scale subsidence over the tropical Indian Ocean prior to convective onset; when intraseasonal easterly acceleration reaches the western extent of a region of intraseasonal upper level westerlies, it produces upper-tropospheric divergence, providing a forcing for upward motion.
Influence Of Upper-Tropospheric Troughs On Tropical Cyclone Intensity Change And Structure : Observational, Reanalysis, And Idealized Numerical Modeling Perspectives, Casey Peirano
Legacy Theses & Dissertations (2009 - 2024)
The interaction between tropical cyclones (TCs) and upper-tropospheric troughs is a
The Simulated Impact Of Snow Cover And Soil Moisture On Convective Precipitation Within The Rocky Mountains Under Climate Warming, Brendan Charles Wallace
The Simulated Impact Of Snow Cover And Soil Moisture On Convective Precipitation Within The Rocky Mountains Under Climate Warming, Brendan Charles Wallace
Legacy Theses & Dissertations (2009 - 2024)
Warm season moist diurnal convection can be particularly sensitive to changes in land surface
Dry Air, Midlevel Flow, And The Persistence Of Deep Convection In Atlantic Tropical Disturbances, Charles Helms
Dry Air, Midlevel Flow, And The Persistence Of Deep Convection In Atlantic Tropical Disturbances, Charles Helms
Legacy Theses & Dissertations (2009 - 2024)
An analysis of dropsonde-observed relative humidity in the Tropical Storm Gabrielle (2013) pregenesis disturbance suggests the presence of a layer of dry air that is being advected into the disturbance from the north. The focus of this study is on this and similar dry air layers, termed dry air inflow pathways (DAIPs), that are characterized by unidirectional disturbance-relative flow drawing dry air into a tropical disturbance. It is hypothesized that DAIPs act to prevent the establishment of persistent deep convection by importing midlevel
Predictability Of African Easterly Waves In An Operational Ensemble Prediction System, Travis J. Elless
Predictability Of African Easterly Waves In An Operational Ensemble Prediction System, Travis J. Elless
Legacy Theses & Dissertations (2009 - 2024)
African easterly waves (AEWs) are the primary synoptic-scale weather feature found in sub-Saharan Africa during boreal summer. Many studies have used observations and idealized models to highlight processes associated with the movement and growth of AEWs, yet there have been few studies documenting the performance of operational ensemble prediction systems (EPSs) for these phenomena. Here, the predictability of AEWs in ECMWF EPS forecasts is assessed during two periods of enhanced AEW activity (July--September 2007--2009 and 2011--2013). Specifically, AEW predictability is analyzed through three main areas of focus: 1) verifying AEW position and intensity forecasts, and assessing their relation to convective …
Global Response To The Madden-Julian Oscillation As A Function Of Phase Speed In Era-Interim Reanalysis And Miroc5 Model Data, Kaitlyn Krzyzaniak
Global Response To The Madden-Julian Oscillation As A Function Of Phase Speed In Era-Interim Reanalysis And Miroc5 Model Data, Kaitlyn Krzyzaniak
Legacy Theses & Dissertations (2009 - 2024)
Many authors state that the phase speed of the Madden–Julian oscillation (MJO) is near 5ms–1, but observations suggest it varies considerably. MJO propagation typically sets off Rossby wave trains that interact with and alter this extratropical pattern; however, differences in the MJO phase speed could alter the Rossby wave response, leading to a unique response in the extratropics. An understanding of the mechanisms and extratropical responses to variable MJO phase speeds would provide innovative and invaluable insight for subseasonal forecasting.
Tropical Cyclone Rapid Intensification In Environments Of Upper-Tropospheric Troughs : Environmental Influences And Convective Characteristics, Michael Fischer
Tropical Cyclone Rapid Intensification In Environments Of Upper-Tropospheric Troughs : Environmental Influences And Convective Characteristics, Michael Fischer
Legacy Theses & Dissertations (2009 - 2024)
Intensity forecasts for tropical cyclones that undergo a period of rapid intensification are particularly susceptible to large errors. For those storms that interact with an upper-tropospheric trough, tropical cyclone intensity forecasts are complicated, as upper-tropospheric troughs can provide unique intensification mechanisms, but are often associated with unfavorable environmental conditions. Although tropical cyclones in environments with nearby upper-tropospheric troughs are associated with lesser intensification rates than tropical cyclones in environments devoid of upper-tropospheric troughs, some tropical cyclone--trough interactions are associated with a period of rapid intensification. This dissertation utilizes reanalysis output, satellite observations, and ensemble modeling simulations to understand whether rapid …
What Affects The Phase Speed Of Madden-Julian Oscillation Convection, Robert Setzenfand
What Affects The Phase Speed Of Madden-Julian Oscillation Convection, Robert Setzenfand
Legacy Theses & Dissertations (2009 - 2024)
The Madden-Julian Oscillation (MJO) is the main source of convective and circulation variability on intraseasonal timescales and planetary spatial scales within the tropics. Although the phase speed of the MJO convective envelope is often stated as 5 m s–1, MJO events that occur over the Indo-Pacific warm pool can have a range of phase speeds. This study uses a wavelet to identify MJO convective events with specified phase speeds in a satellite-derived outgoing longwave radiation (OLR) dataset during boreal winter. The wavelet-filtered OLR index is then regressed against basic meteorological variables to extract information about MJO events or signals propagating …
Influence Of Lightning-Producing Convection On Tropical Cyclone Intensity Change, Stephanie Stevenson
Influence Of Lightning-Producing Convection On Tropical Cyclone Intensity Change, Stephanie Stevenson
Legacy Theses & Dissertations (2009 - 2024)
Lightning observations in tropical cyclones (TCs) over the ocean are a recent advance- ment, and while many studies have noted relationships between lightning and TC intensity change, the relationships are not consistent. This dissertation aims to understand the com- plexities of the relationships between lightning and TC intensity change, and associate the relationships to storm kinematic, thermodynamic, and microphysical processes.
Agricultural Drought Transition Periods In The United States Corn Belt Region, Nicholas Joseph Schiraldi
Agricultural Drought Transition Periods In The United States Corn Belt Region, Nicholas Joseph Schiraldi
Legacy Theses & Dissertations (2009 - 2024)
Agricultural drought in the U.S. Corn Belt region (CBR) has tremendous global socioeconomic implications. Unfortunately, the weather and climate factors that contribute to transition events toward or away from such droughts, and how well those factors are predicted, are poorly understood. This dissertation focuses on the atmospheric circulation signals associated with agricultural drought transitions periods in the CBR that evolve over 20 and 60 days, and how well those circulation signals are predicted on seasonal to sub-seasonal time scales.
A Synoptic Climatology Of Combined Severe/Weather/Flash Flood Events, Kyle James Pallozzi
A Synoptic Climatology Of Combined Severe/Weather/Flash Flood Events, Kyle James Pallozzi
Legacy Theses & Dissertations (2009 - 2024)
Classical forms of severe weather such as tornadoes, damaging convective wind gusts, and large hail, as well as flash flooding events, all have potentially large societal impacts. This impact is further magnified when these hazards occur simultaneously in time and space. A major challenge for operational forecasters is how to accurately predict the occurrence of combined storm hazards, and how to communicate the associated multiple threat hazards to the public. A seven-year climatology (2009-2015) of combined severe weather/flash flooding (SVR/FF) events across the contiguous United States was developed in attempt to study the combined SVR/FF event hazards further.
The Variability Of Madden-Julian Oscillation Convection And The Role Of The Western Hemisphere Circulation, Naoko Sakaeda
The Variability Of Madden-Julian Oscillation Convection And The Role Of The Western Hemisphere Circulation, Naoko Sakaeda
Legacy Theses & Dissertations (2009 - 2024)
The convective initiation of the Madden-Julian Oscillation (MJO) over the Indian basin is often associated with eastward-propagating intraseasonal circulation approaching from the Western Hemisphere (WH), which is suggested to influence the onset of MJO convection. This dissertation first documents the event-to-event variability in the characteristics of MJO convection, which shows a geographical discrepancy in the relative roles of moist and dry dynamics on MJO convection. This dissertation then examines the structural evolution and dynamics of the intraseasonal upper-tropospheric circumnavigating circulation over the WH and its subsequent impact on MJO convection over the Indian basin, where MJO convective characteristics are highly …
Associations Between The Madden-Julian Oscillation, Equatorial Rossby Waves, And Extratropical Northern Hemisphere Predictability, Lawrence Gloeckler
Associations Between The Madden-Julian Oscillation, Equatorial Rossby Waves, And Extratropical Northern Hemisphere Predictability, Lawrence Gloeckler
Legacy Theses & Dissertations (2009 - 2024)
The Madden-Julian oscillation (MJO), the leading mode of tropical convective and circulation variability on intraseasonal time scales, has become increasingly leveraged to improve empirical prediction of the global atmospheric circulation. Significant progress has been made in recent years to advance subseasonal (10-30-day) prediction of atmospheric circulation anomalies, and much of this progress can be attributed to the inclusion of information about the phase and amplitude of the MJO in various forecast processes. Despite this progress, however, forecasts based only on the state of the MJO omit information about other important tropical convective and circulation anomalies, and coherent MJO signals are …
The Spectrum Of Progressive Derecho Formation Environments, Corey Guastini
The Spectrum Of Progressive Derecho Formation Environments, Corey Guastini
Legacy Theses & Dissertations (2009 - 2024)
Progressive derechos are severe mesoscale convective systems that often form east of the Rocky Mountains during the warm season (May–August) and cause, by definition, straight-line wind damage along paths upwards of 400 km long. This study develops a subjective, seven-category classification scheme that spans the spectrum of progressive derecho formation environments from those dominated by robust upper-level ridges to those characterized by vigorous upper-level troughs. A climatology of 256 progressive derecho events is created for 1996–2013 and is categorized according to the developed classification scheme. Derecho initiation-relative composites are constructed for each of the seven groups using 0.5° Climate Forecast …
On The Mjo And Anticyclonic Wavebreaking, Kyle Macritchie
On The Mjo And Anticyclonic Wavebreaking, Kyle Macritchie
Legacy Theses & Dissertations (2009 - 2024)
The Madden Julian oscillation (MJO) is the primary mode of intraseasonal variability in the tropics. The MJO often couples with convection as it moves over the Indian Ocean and decouples as it leaves the west Pacific Ocean. The association between convection coupled to the MJO and the midlatitude flow pattern has been the primary focus of numerous studies. In particular, it has been shown that there is a statistical relationship between the position and strength of the MJO and anticyclonic wavebreaking (AWB). This study expands on this statistical relationship by examining, in detail, the two-way relationship between the MJO and …
Interactions Between African Easterly Waves And Moist Convection, Matthew Adam Janiga
Interactions Between African Easterly Waves And Moist Convection, Matthew Adam Janiga
Legacy Theses & Dissertations (2009 - 2024)
African easterly waves (AEWs) over tropical Africa and the East Atlantic influence and are themselves influenced by moist convection. Data from the Tropical Rainfall Measuring Mission (TRMM) satellite, reanalyses, and in-situ observations are used to examine both directions of this two-way interaction.
Analysis Of Intraseasonal Convective Variability Modes Over West Africa During The Monsoon Season, Jeffrey Ceratto
Analysis Of Intraseasonal Convective Variability Modes Over West Africa During The Monsoon Season, Jeffrey Ceratto
Legacy Theses & Dissertations (2009 - 2024)
Intraseasonal variability of rainfall within the West African Monsoon has been shown to be an important factor in the weather of this region. Multiple factors have been found to contribute to variability at this timescale. Mounier, et al (2008) use EOF analysis to uncover and describe a quasi-stationary dipole of precipitation between the West African Monsoon system and the West Atlantic/Caribbean Sea. This mode, termed the Quasi Biweekly Zonal Dipole mode, operates on timescales of roughly 13 days. The stationary nature of this dipole is focused upon in their work, while the role of Kelvin waves in the mode are …
Multiscale Analyses Of Inland Tropical Cylcone--Midlatitude Jet Interactions : Camille (1969) And Danny (1997), Matthew S. Potter
Multiscale Analyses Of Inland Tropical Cylcone--Midlatitude Jet Interactions : Camille (1969) And Danny (1997), Matthew S. Potter
Legacy Theses & Dissertations (2009 - 2024)
TC Camille (1969) and TC Danny (1997) both interacted with the equatorward entrance region of an upper-tropospheric jet as they traversed the Appalachian Mountains; however, their societal impacts differed. During the 12-h period starting 0000 UTC 20 August 1969, 690 mm of rain fell over Massies Mill, Virginia, as TC Camille traversed the central Appalachian Mountains. On 24 July 1997, TC Danny underwent inland reintensification while moving across the Carolinas. TC Danny's minimum central mean sea level pressure decreased from 1012 hPa to 1000 hPa and its maximum sustained wind speed increased from 20 kt to 40 kt during the …
Convectively-Coupled Kelvin Waves Over The Tropical Atlantic And African Regions And Their Influence On Atlantic Tropical Cyclogenesis, Michael John Ventrice
Convectively-Coupled Kelvin Waves Over The Tropical Atlantic And African Regions And Their Influence On Atlantic Tropical Cyclogenesis, Michael John Ventrice
Legacy Theses & Dissertations (2009 - 2024)
High-amplitude convectively coupled atmospheric Kelvin waves (CCKWs) are explored over the tropical Atlantic during the boreal summer. Atlantic tropical cyclogenesis is found to be more frequent during the passage of the convectively active phase of the CCKW, and most frequent two days after its passage. CCKWs impact convection within the mean latitude of the inter-tropical convergence zone over the northern tropical Atlantic. In addition to convection, CCKWs also impact the large scale environment that favors Atlantic tropical cyclogenesis (i.e., deep vertical wind shear, moisture, and low-level relative vorticity).
The Influence Of The Great Lakes On Mcs Formation And Development In The Warm Season, Alan Frederick Srock
The Influence Of The Great Lakes On Mcs Formation And Development In The Warm Season, Alan Frederick Srock
Legacy Theses & Dissertations (2009 - 2024)
This study focuses on how near-surface thermal boundaries that form near the Great Lakes during the warm season can contribute to the formation of mesoscale convective systems (MCSs). Differential heating across land-water interfaces can create a cold dome of air over the lake; convection may develop when the relatively-cold dome of air becomes deep enough to enable air parcels that intersect these boundaries to reach their level of free convection. A radar-based climatology of MCS events surrounding the Great Lakes for 2002-2005 showed that MCSs frequently form in the vicinity of the Great Lakes. Composites of MCS events over the …
Role Of Equatorial Waves In Tropical Cyclogenesis, Carl J. Schreck, Iii
Role Of Equatorial Waves In Tropical Cyclogenesis, Carl J. Schreck, Iii
Legacy Theses & Dissertations (2009 - 2024)
Tropical cyclones typically form within preexisting wavelike disturbances that couple with convection. Using Tropical Rainfall Measuring Mission (TRMM) multisatellite rainfall estimates, this study determines the relative number of tropical cyclones that can be attributed to various wave types, including the Madden-Julian oscillation (MJO), Kelvin waves, equatorial Rossby (ER) waves, mixed Rossby-gravity (MRG) waves, and tropical depression (TD)-type disturbances. Tropical cyclogenesis is attributed to an equatorial wave's convection when the filtered rainfall anomaly exceeds a threshold value at the genesis location.
African Easterly Waves And Convection, Gareth James Berry
African Easterly Waves And Convection, Gareth James Berry
Legacy Theses & Dissertations (2009 - 2024)
In this research the physical mechanisms relating synoptic scale African Easterly Waves (AEWs) and convection are explored using a variety of analysis techniques.