Browsing by Author "Rutledge, Steven A., advisor"
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Item Open Access A polarimetric radar analysis of convection observed during NAME and TiMREX(Colorado State University. Libraries, 2011) Rowe, Angela Kaye, author; Rutledge, Steven A., advisor; Johnson, Richard H., committee member; Van den Heever, Susan C., committee member; Lang, Timothy James, committee member; Eykholt, Richard Eric, 1956-, committee memberThe mountainous regions of northwestern Mexico and southwestern Taiwan experience periods of intense rainfall associated with the North American and Asian monsoons, respectively, as warm, moist air is ushered onshore due to a reversal of mean low-level winds. Potentially unstable air is lifted along the steep topography, leading to convective initiation over the high peaks and adjacent foothills in both regions. In addition, an enhancement of convection in preexisting systems is observed due to interaction with the terrain, leading to localized heavy rain along the western slopes. The predictability of warm-reason rainfall in these regions is limited by the lack of understanding of the nature of these precipitating features, including the diurnal variability and elevation-dependent trends in microphysical processes. Using polarimetric data from NCAR's S-band, polarimetric radar (S-Pol), deployed during the North American Monsoon Experiment (NAME) and Terrain-influenced Monsoon Rainfall Experiment (TiMREX), individual convective elements were identified and tracked, allowing for an analysis of hydrometeor characteristics within evolving cells. Furthermore, a feature classification algorithm was applied to these datasets to compare characteristics associated with isolated convection to cells contained within organized systems. Examples of isolated cells from a range of topography during NAME revealed the presence of ZDR columns, attributed to the lofting of drops above the melting level, where subsequent freezing and growth by riming led to the production of graupel along the western slopes of the Sierra Madre Occidental (SMO) and adjacent coastal plain. Melting of large ice hydrometeors was also noted over higher terrain, leading to short-lived yet intense rainfall despite truncated warm-cloud depths compared to cells over the lower elevations. Cells embedded within mesoscale convective systems (MCSs) during NAME also displayed the combined roles of warm-rain and ice-based microphysical processes as convection organized along the terrain. In addition to enhancing precipitation along the western slopes of the SMO, melting ice contributed to the production of mesoscale outflow boundaries, which provided an additional focus mechanism for convective initiation over the lower elevations and resulted in propagation of these systems toward the coast. Intense rainfall was also observed along the Central Mountain Range (CMR) in Taiwan; however, in contrast to the systems during NAME, this enhancement occurred as MCSs moved onshore within the southwesterly flow and intercepted the CMR's steep slopes. Elevated maxima in polarimetric variables, similar to observations in convection during NAME, indicated a contribution from melting ice to rainfall at these higher elevations. Vertical profiles of ice mass, however, revealed greater amounts throughout the entire vertical depth of convection during NAME. In addition, isolated cells during TiMREX were relatively shallow compared to organized convection in both regions. Nonetheless, instantaneous rain rates were comparable during both experiments, suggesting efficient warm-rain processes within convection observed in the TiMREX radar domain and emphasizing a range of microphysical processes in these two regions. In addition, the greatest contribution to hourly accumulated rain mass in these regions was associated with deep organized systems along the western slopes, posing threats along the steep topography due to flash flooding and subsequent landslides, emphasizing the need for accurate prediction and understanding of the processes that lead to intense rainfall in these vulnerable regions.Item Open Access Analysis and application of the CASA IP1 X-band polarimetric radar network(Colorado State University. Libraries, 2009) Dolan, Brenda, author; Rutledge, Steven A., advisorThe Collaborative Adaptive Sensing of the Atmosphere's Integrated Project 1 (CASA IP1) network of four X-band, polarimetric, Doppler, adaptively scanning radars is investigated for studying storm microphysics and kinematics. The complications of non-Rayleigh scattering and attenuation at X-band are explored for impact on microphysical interpretation. The rapid and adaptive scanning strategy is evaluated for application of dual-Doppler techniques to retrieve the 3-D wind field, and general understanding of storm interactions. Several rain rate algorithms are invoked to estimate surface rainfall. A case study from 10 June 2007 illustrates the capabilities and limitations of using the IP1 network for studies of storm interactions, and lightning data are analyzed to relate these interactions to storm electrification. The nearby S-band, polarimetric KOUN radar is studied for comparison. Scattering simulations using the T-matrix model are performed on seven hydrometeor types (excluding hail) to understand the non-Rayleigh effects at X-band compared with S-band. The simulations show the greatest non-linearities in Zdr and Kadp of rain and graupel. Results of the simulations are used to develop a specific X-band fuzzy logic hydrometeor identification algorithm (HID) for diagnosing bulk regions of hydrometeors. Attenuation and non-Rayleigh scattering are present in the IP1 data, but with mitigation techniques these have minimal impact on the analysis. The high temporal resolution is integral in resolving up- and downdrafts, as well as hydrometeor evolution, but the inconsistent and lack of upper-level coverage are significant limitations for quantitative analysis of kinematic and microphysical relationships. Observations using IP1 data of a storm on 10 June 2007 show the development of the updraft, subsequent graupel echo volume evolution, and onset of lightning. Development of the downdraft is preceded by large volumes of graupel in the mid-levels. A second peak in intra-cloud lightning is observed to be associated with an increase in height of the upper positive charge, resulting from a kinematic intensification. Many of these trends are corroborated by KOUN. Rain rate estimation comparisons show that the X-band blended algorithm performs better compared with ground-based sensors than the simple Z-R relationship and employs polarimetric estimators more often than S-band blended methods.Item Open Access Boundary layer features observed during NAME 2004(Colorado State University. Libraries, 2011) Stuckmeyer, Elizabeth Anne, author; Rutledge, Steven A., advisor; Johnson, Richard H., committee member; Weckwerth, Tammy M., 1966-, committee member; Ramírez, Jorge A., committee memberS-Pol radar data from the North American Monsoon Experiment (NAME) are examined to investigate the characteristics of sea breezes that occurred during the North American Monsoon in the late summer of 2004, as well as their role in modulating monsoon convection. Zero degree plan position indicated (PPI) scans were examined to determine the presence of a sea breeze fine line in the S-Pol radar data. Sea breeze fine lines were typically observed over land very near the coast of the Gulf of California (GoC), and usually moved onshore around 1700-1800 UTC (11:00 AM - 12:00 PM local time), and then continued to move slowly inland on the coastal plain. The sea breezes typically moved on land and dissipated before any significant interactions with Sierra Madre Occidental (SMO) convection could occur. Fine lines varied in reflectivity strength, but were typically around 10 to 20 dBZ. Surface winds from the Estación Obispo (ETO) supersite were analyzed to confirm the presence of a shift in wind direction on days in which a fine line had been identified. Typically winds changed from light and variable to consistently out of the west or southwest. Vertical plots of S-Pol reflectivity were created to examine sea breeze structure in the vertical, but these were not found to be useful as the sea breeze signature was nearly impossible to distinguish from other boundary layer features. Horizontal structure was further investigated using wind profiler relative reflectivity, vertical velocity, and horizontal winds from the profiler located at ETO. Relative reflectivity and vertical velocity fields revealed a complex boundary layer structure on some days of repeating updrafts and downdrafts. Further examination of S-Pol PPI data revealed that these vertical motions are likely due to the presence of horizontal convective rolls. Profiler horizontal winds revealed that the depth and vertical structure of the sea breezes varied significantly from day to day, but that the height of the sea breeze is around 1 km above the ground. Sea breezes observed during NAME almost never initiated convection on their own. It is hypothesized that a weak thermal contrast between the GoC and the land leads to comparatively weak sea breezes, which don't have enough lift to trigger convection.Item Open Access Characteristics and organization of precipitating features during NAME 2004 and their relationship to environmental conditions(Colorado State University. Libraries, 2008) Pereira, Luis Gustavo P., author; Rutledge, Steven A., advisor; Johnson, Richard H., committee member; Kummerow, Christian D., committee member; Cifelli, Robert C., committee member; Chandrasekar, V., committee memberThe focus of this study is to examine the characteristics of convective precipitating features (PFs) during the 2004 North American Monsoon Experiment (NAME) and their precursor environmental conditions. The goal is to gain a better insight into the predictability and variability of warm season convective processes in the southern portion of the North American Monsoon core region. The organization and characteristics of PFs are evaluated using composite radar reflectivity images over the southern portion of the Gulf of California. The environmental conditions are assessed using satellite images and a plethora of atmospheric observational analysis maps, such as winds at multiple levels, upper-level divergence, vorticity, vertical air motion, moisture and vertical cross-sections. Our study reveals that most PFs occurred during the afternoon and evening over land, especially near the foothills of the Sierra Madre Occidental. The vast majority of the precipitating features (~95%) were small, isolated, unorganized, short-lived convective cells. Mesoscale convective systems (MCSs) made up only 5% of the PF population. Nonetheless, these large, long-lived, precipitating features were responsible for 72% of the total precipitation within the radar composite region. An analysis of the number and rainfall produced by these MCSs revealed that they were not constant from day to day, but rather, varied significantly throughout NAME. We found that MCSs were more frequent when the atmosphere is thermodynamically unstable and the wind shear or large-scale dynamics favors the development of organized convection. Lastly, we examined the synoptic conditions associated with episodes of above average MCS rainfall in the southern portion of the NAME core region. Tropical waves were found to be an essential source of moisture and instability in the region. We also found that transient upper-level inverted troughs interact with the upper-level anticyclone to produce a "North American Monsoon Jet Streak" that created favorable dynamical uplift and wind shear conditions for MCS development.Item Open Access Cloud-to-ground lightning polarity and environmental conditions over the central United States(Colorado State University. Libraries, 2007) Kalb, Christina P., author; Rutledge, Steven A., advisor; Cotton, William R., committee member; Robinson, Steven R., committee memberThe majority of cloud-to-ground (CG) lightning across the United States lowers negative charge to the ground. However, recent studies have documented storms that produce an abundance of positive CG lightning. These positive storms have been shown to occur in different mesoscale regions on the same days, and in different thermodynamic environments. This study uses radar data, and CG lightning data, to identify positive and negative storms that occurred in the region between the Rocky Mountains and the Mississippi River. The thermodynamic conditions in the environment of these storms are derived from the Rapid Update Cycle model analysis, where the point nearest to the storm, in the direction of storm motion was used. Considerable scatter was present in the final results that limited the extent of the trends seen. Out of all the variables used, cloud base height, dew point, 850-500 mb lapse rate, and warm cloud depth showed the most difference between the positive and negative storms. Positive storms tended to occur with lower cloud base heights, higher dew points, smaller 850-500 mb lapse rates, and lower warm cloud depths. Little trend was seen for CAPE, CIN, freezing level, lifted index, mean relative humidity, mid-level relative humidity, precipitable water 0-3 km wind shear, 0-6 km wind shear, storm relative helicity, and Se. The strength of the differences seen between the positive and negative storms varies with the choice of percent positive used. Differences between the positive and negative storms tended to decrease when 10% was chosen (as compared to 30%), but they increased when 50% was chosen.Item Open Access Development of a polarimetric radar based hydrometeor classification algorithm for winter precipitation(Colorado State University. Libraries, 2012) Thompson, Elizabeth Jennifer, author; Rutledge, Steven A., advisor; Dolan, Brenda, committee member; Chandrasekar, V., committee member; van den Heever, Susan, committee memberThe nation-wide WSR-88D radar network is currently being upgraded for dual-polarized technology. While many convective, warm-season fuzzy-logic hydrometeor classification algorithms based on this new suite of radar variables and temperature have been refined, less progress has been made thus far in developing hydrometeor classification algorithms for winter precipitation. Unlike previous studies, the focus of this work is to exploit the discriminatory power of polarimetric variables to distinguish the most common precipitation types found in winter storms without the use of temperature as an additional variable. For the first time, detailed electromagnetic scattering of plates, dendrites, dry aggregated snowflakes, rain, freezing rain, and sleet are conducted at X-, C-, and S-band wavelengths. These physics-based results are used to determine the characteristic radar variable ranges associated with each precipitation type. A variable weighting system was also implemented in the algorithm's decision process to capitalize on the strengths of specific dual-polarimetric variables to discriminate between certain classes of hydrometeors, such as wet snow to indicate the melting layer. This algorithm was tested on observations during three different winter storms in Colorado and Oklahoma with the dual-wavelength X- and S-band CSU-CHILL, C-band OU-PRIME, and X-band CASA IP1 polarimetric radars. The algorithm showed success at all three frequencies, but was slightly more reliable at X-band because of the algorithm's strong dependence on specific differential phase. While plates were rarely distinguished from dendrites, the latter were satisfactorily differentiated from dry aggregated snowflakes and wet snow. Sleet and freezing rain could not be distinguished from rain or light rain based on polarimetric variables alone. However, high-resolution radar observations illustrated the refreezing process of raindrops into ice pellets, which has been documented before but not yet explained. Persistent, robust patterns of decreased correlation coefficient, enhanced differential reflectivity, and an inflection point around enhanced reflectivity occurred over the exact depth of the surface cold layer indicated by atmospheric soundings during times when sleet was reported at the surface. It is hypothesized that this refreezing signature is produced by a modulation of the drop size distribution such that smaller drops preferentially freeze into ice pellets first. The melting layer detection algorithm and fall speed spectra from vertically pointing radar also captured meaningful trends in the melting layer depth, height, and mean correlation coefficient during this transition from freezing rain to sleet at the surface. These findings demonstrate that this new radar-based winter hydrometeor classification algorithm is applicable for both research and operational sectors.Item Open Access Intraseasonal and diurnal variations of precipitation features observed during DYNAMO(Colorado State University. Libraries, 2020) Rocque, Marquette N., author; Rutledge, Steven A., advisor; Maloney, Eric D., committee member; Chandrasekar, V., committee memberThe diurnal cycle (DC) of rainfall over the tropical oceans and within the Madden–Julian oscillation (MJO) has been investigated in numerous studies, but there has been limited research on how the DC of precipitation and convective organization evolve throughout phases of the MJO over the open ocean. Cloud and precipitation parameterizations in models have been the source of low MJO predictability, so understanding the fundamental convective processes occurring within the MJO, both on the intraseasonal and diurnal timescales, will be beneficial in improving these model simulations. This study employs measurements collected during the Dynamics of the MJO (DYNAMO) field campaign (1 Oct. – 4 Dec. 2011) to investigate how the distribution of precipitation features (PFs) varies across MJO phase groups, throughout the day, and on-/off-equator. PFs identified from radar volume scans at the R/V Roger Revelle (80.5°E, 0°N) and R/V Mirai (80.5°E, 8°S) were classified into five morphologies based on shape and size. Additionally, several environmental parameters including sea surface temperature (SST), convective available potential energy (CAPE), and latent and sensible heat fluxes were analyzed to understand local interactions between the ocean, atmosphere, and convection. The largest rain events occurred during MJO phases 2&3 at the Revelle. Mesoscale events were found in all phase groups at the Mirai. However, convection was generally weaker at the Mirai, most likely due to extremely dry air (RH < 20%) in the mid-troposphere, and little variation in SST. Two westerly wind bursts (WWBs) were observed in phases 2&3 of the second MJO event (21–30 Nov.) at the Revelle which enhanced surface winds and air–sea fluxes and allowed stratiform precipitation to persist. Additionally, these WWBs enhanced the near-surface equatorial current known as the Yoshida–Wyrtki jet, which caused a large amount of upper ocean mixing and significantly cooled SSTs into December. The DC of rainfall was greatest during phases 8&1 and 2&3 at the Revelle with peaks in rain rate occurring in the afternoon and early morning hours. The afternoon peak was attributed to isolated and sub-MCS nonlinear PFs, apparently forced by SST heating and significant air–sea fluxes. These features then grew upscale through the evening into MCS nonlinear events, peaking in intensity just after midnight. MCS nonlinear features contributed the most to the rain volume during phases 2&3 at the Revelle at roughly 70%. Isolated and sub-MCS nonlinear features were the dominant mode of convection during the suppressed phases at the Revelle (4&5 and 6&7). Mesoscale systems were not observed in these two phase groups. MCS nonlinear systems were found in at least 15% of all radar scans for each phase group at the Mirai, and there was significantly less variability in environmental parameters between phase groups. Additionally, the DC of SST at the Mirai was much weaker than at the Revelle, which was attributed to enhanced surface winds that mixed out any diurnal warm layers. Thus, it was found the MJO had little modulation on the local environment off-equator.Item Open Access Lightning channel locations, LNOx production, and advection in anomalous and normal polarity thunderstorms(Colorado State University. Libraries, 2018) Davis, Trenton, author; Rutledge, Steven A., advisor; Barth, Mary, committee member; Fischer, Emily, committee member; Reising, Steven, committee memberTropospheric ozone is a powerful greenhouse gas and OH precursor, thus understanding its sources is important. Its production is also widely studied in atmospheric science today as global climate modelers attempt to estimate future warming within the troposphere. Nitrogen oxides (NO + NO2 = NOx), serve as a precursor to ozone production. In areas where higher concentrations of OH are present, NOx will undergo reactions to produce nitric acid, thereby shortening its lifetime and limiting the production of ozone. Due to lower concentrations of OH in the upper troposphere, NOx tends to experience a longer lifetime (on the order of days) and greater ozone production at these heights. Lightning produces an appreciable amount of NOx (a.k.a. LNOx) but the final distribution of resulting LNOx, and thus its ozone production, remains poorly understood. Therefore, it is important that this source of NOx be further investigated to improve current LNOx parameterizations. Numerical modeling methods attempt to study this issue by parameterizing the nature of lightning within thunderstorms. Often, the vertical distribution of flash channels (and LNOx) is produced according to a parameterized flash rate within a defined vertical profile and reflectivity volume threshold. The structure and intensity of thunderstorms are highly variable though, causing the location of lightning within a thunderstorm to differ from one thunderstorm to the next. Furthermore, one remaining goal of the Deep Convective Clouds and Chemistry (DC3) field campaign (May – June 2012) was to compare the lightning flash locations and contributions to upper tropospheric LNOx between storms of normal and anomalous charge polarity. To address this remaining goal, five cases with over 5600 total flashes are analyzed in detail using data from DC3, three in northern Colorado and two in northern Alabama. Lightning sources are combined into 3-dimensional (3-D) flash channels and flash channel parcels, with each parcel containing the LNOx produced by its parent flash channel. Parcels are then advected forward in time during the lifetime of each storm using 3-D wind fields produced from dual-Doppler analyses. Results reveal a greater number of flashes and flash channels within anomalous polarity thunderstorms compared to normal polarity thunderstorms at a mean initiation height around 5 km. Flashes in these storms also appear to transect areas of higher vertical velocities resulting in roughly half of flash channel parcels being advected to the upper troposphere (z > 8 km). Contrary to some assumptions, an appreciable fraction of these parcels and NOx contributions remain in the boundary layer of these storms. In the two normal polarity thunderstorm cases, flash channels tend to initiate around 8 km with roughly half of the flash channel parcels remaining near or above 8 km. While both storm types appear to transport roughly 50% of their flash channel parcels to the upper troposphere, significantly larger flash counts and total flash length in the anomalous polarity storms lead to much higher mixing ratios of LNOx in the upper troposphere. These results may help chemistry modelers in parameterizing LNOx formation in both normal and anomalous thunderstorm polarity structures, which will also improve global climate model parameterizations of tropospheric ozone production.Item Open Access Radar and lightning analyses of gigantic jet-producing storms(Colorado State University. Libraries, 2012) Meyer, Tiffany C., author; Rutledge, Steven A., advisor; Lang, Timothy, committee member; Robinson, Raymond, committee member; Schumacher, Russ, committee memberAn analysis of the storm structure and evolution associated with six gigantic jets was conducted. Three of these gigantic jets were observed within detection range of very high-frequency lightning mapping networks. All six were within range of operational radars and two-dimensional lightning network coverage: five within the National Lightning Detection Network and one within the Global Lighting Detection network. Most of the storms producing the jets formed in a high CAPE, low lifted index environments and had maximum reflectivity values of 54 to 62 dBZ and 10-dBZ echo tops reaching 14-17 km. Most storms were near the highest lighting flash rate and peak storm intensity with an overshooting echo top just before or after the time of the jet. The overshooting top and strong intensification may have indicated a convective surge which allowed the upper positive charge to mix with a negatively charged screening layer that became depleted. Intra-cloud lightning initiating in the mid-level negative region could have exited upward through the recently depleted positive region, producing a gigantic jet.Item Open Access The climatology of lightning producing large impulse charge moment changes with an emphasis on mesoscale convective systems(Colorado State University. Libraries, 2013) Beavis, Nicholas, author; Rutledge, Steven A., advisor; Schumacher, Russ S., committee member; Lyons, Walter A., committee member; Lang, Timothy J., committee member; Eykholt, Richard E., committee memberThe use of both total charge moment change (CMC) and impulse charge moment change (iCMC) magnitudes to assess the potential of a cloud-to-ground (CG) lightning stroke to induce a mesospheric sprite has been well described in literature. However, this work has primarily been carried out on a case study basis. To complement these previous case studies, climatologies of regional, seasonal, and diurnal observations of large-iCMC discharges are presented. In this study, large-iCMC discharges for thresholds > 100 and > 300 C km in both positive and negative polarities are analyzed on a seasonal basis using density maps of 2° by 2° resolution across the conterminous U.S. using data from the Charge Moment Change Network (CMCN). Also produced were local solar time diurnal distributions in eight different regions covering the lower 48 states as well as the Atlantic Ocean, including the Gulf Stream. In addition, National Lightning Detection Network (NLDN) cloud-to-ground (CG) flash diurnal distributions were included. The seasonal maps show the predisposition of large positive iCMCs to dominate across the Northern Great Plains, with large negative iCMCs favored in the Southeastern U.S. year-round. During summer, the highest frequency of large positive iCMCs across the Upper Midwest aligns closely with the preferred tracks of nocturnal mesoscale convective systems (MCSs). As iCMC values increase above 300 C km, the maximum shifts eastward of the 100 C km maximum in the Central Plains. The Southwestern U.S. also experiences significant numbers of large-iCMC discharges in summer, presumably due to convection associated with the North American Monsoon (NAM). The Gulf Stream is active year round, with a bias towards more large positive iCMCs in winter. Diurnal distributions in the eight regions support these conclusions, with a nocturnal peak in large-iCMC discharges in the Northern Great Plains and Great Lakes, an early- to mid-afternoon peak in the Intermountain West and the Southeastern US, and a morning peak in large-iCMC discharge activity over the Atlantic Ocean. Large negative iCMCs peak earlier in time than large positive iCMCs, attributed to the maturation of large stratiform charge reservoirs after initial convective development. Results of eight case studies of Northern Great Plains MCSs using the NMQ National Radar Mosaic dataset are also presented. Thresholds described above were used to disseminate iCMC discharges within the MCSs. The radar analysis algorithm on a 5-minute radar volume basis included convective-stratiform partitioning, association of iCMCs and CGs to their respective storms, and statistical analysis on large (100-300 C km) and sprite-class (>300 C km) iCMC-producing storms. Results from these case studies indicated a strong preference of sprite-class iCMCs to be positive and located in stratiform-identified regions. A 2-3 hour delay in the maximum activity of sprite-class iCMCs after the maximum large iCMC activity was noted, and was strongly correlated with the maximum areal coverage of stratiform area. A loose correlation between more frequent sprite-class iCMC production and larger stratiform areas was noted, suggesting that larger stratiform areas are simply more capable, not more likely, to produce high sprite-class iCMC rates. Enhanced maximum convective echo heights corresponded to enhanced sprite-class iCMC activity in stratiform areas, attributed in part to enhanced charge advection from the convective line. In situ charging was also presumed to have a significant role in charge generation leading to sprite-class iCMC discharges in stratiform regions.Item Open Access The simultaneous influence of thermodynamics and aerosols on deep convection and lightning(Colorado State University. Libraries, 2016) Stolz, Douglas C., author; Rutledge, Steven A., advisor; Pierce, Jeffrey R., committee member; van den Heever, Susan C., committee member; Reising, Steven C., committee memberThe dissertation consists of a multi-scale investigation of the relative contributions of thermodynamics and aerosols to the observed variability of deep convective clouds in the Tropics. First, estimates of thermodynamic quantities and cloud-condensation nuclei (CCN) in the environment are attributed to convective features (CFs) observed by the Tropical Rainfall Measuring Mission (TRMM) satellite for eight years (2004-2011) between 36⁰S-36⁰N across all longitudes. The collection of simultaneous observations was analyzed in order to assess the relevance of thermodynamic and aerosol hypotheses for explaining the spatial and temporal variability of the characteristics of deep convective clouds. Specifically, the impacts of normalized convective available potential energy (NCAPE) and warm cloud depth (WCD) as well as CCN concentrations (D ≥ 40 nm) on total lightning density (TLD), average height of 30 dBZ echoes (AVGHT30), and vertical profiles of radar reflectivity (VPRR) within individual CFs are the subject of initial curiosity. The results show that TLD increased by up to 600% and AVGHT30 increased by up to 2-3 km with increasing NCAPE and CCN for fixed WCD on the global scale. The partial sensitivity of TLD/AVGHT30 to NCAPE and CCN individually are found to be comparable in magnitude, but each independent variable accounts for a fraction of the total range of variability observed in the response (i.e., when the influences of NCAPE and CCN are considered simultaneously). Both TLD and AVGHT30 vary inversely with WCD such that maxima of TLD and AVGHT30 are found for the combination of high NCAPE, high CCN, and shallower WCD. The relationship between lightning and radar reflectivity is shown to vary as a function of CCN for a fixed thermodynamic environment. Analysis of VPRRs shows that reflectivity in the mixed phase region (altitudes where temperatures are between 0⁰C and -40⁰C) is up to 5.0-5.6 dB greater for CFs in polluted environments compared to CFs in pristine environments (holding thermodynamics fixed). A statistical decomposition of the relative contributions of NCAPE, CCN, and WCD to the variability of convective intensity proxies is undertaken. Simple linear models of TLD/AVGHT30 based on the predictor set composed of NCAPE, CCN, and WCD account for appreciable portions of the variability in convective intensity (R2 ≈ 0.3-0.8) over the global domain, continents, oceans, and select regions. Furthermore, the results from the statistical analysis suggest that the simultaneous contributions from NCAPE, CCN, and WCD to the variability of convective intensity are often comparable in magnitude. There was evidence for similar relationships over even finer-scale regions [O(106 km2)], but differences in the relative prognostic ability and stability of individual regression parameters between regions/seasons were apparent. These results highlight the need to investigate the connection between statistical behavior and local meteorological variability within individual regions. Following the global and regional analyses, data from Dynamics of the Madden-Julian Oscillation (DYNAMO) field campaign (2011-2012; central equatorial Indian Ocean (CIO)) and other sources was used to assess the relative impact of aerosols on deep convective clouds within a fine-scale environment with spatially homogeneous thermodynamics and variable aerosols in a pristine background over the CIO (CCN ~50-100 cm-3, on average; NCAPE and WCD are hypothesized to be approximately constant, spatially). The experiment was designed to compare differences in the convective cloud population developing in more-polluted and pristine regions, north and south of the equator, respectively. Analysis of the covariability of rainfall, cold cloud frequency, CCN, NCAPE, and lightning/radar reflectivity in deep convective clouds over multiple (> 20) episodes of the Madden-Julian Oscillation (MJO) leads to a hypothesis for a potential bi-directional interaction between aerosols and convective clouds that develop in association with the MJO. Close scrutiny of the results from climatology leads to the conclusion that thermodynamics and aerosols both influence deep convective cloud behavior over the CIO in a manner similar to that observed on the global scale, but the possibility that other factors are required to reproduce the full range of variability of deep convective clouds on fine-scales is acknowledged. The research presented in this dissertation constitutes one of the first efforts to link the documented variability of radar reflectivity and lightning within convective features observed by the TRMM satellite to their environment using novel representations of thermodynamic and aerosol quantities from reanalysis and a chemical transport model, respectively. The independent variables studied here (i.e., NCAPE, CCN, and WCD) were chosen specifically to address preeminent hypotheses in the literature and the results from this investigation suggest that NCAPE, CCN, and WCD each contribute significantly to the variability of deep convective clouds throughout the Tropics and Subtropics (and perhaps seasonally). Implications of the findings from the current investigations and the relevance of these results to future studies are discussed.Item Open Access Tropical warm pool rainfall variability and impact on upper ocean variability throughout the Madden-Julian Oscillation(Colorado State University. Libraries, 2016) Thompson, Elizabeth J., author; Rutledge, Steven A., advisor; Moum, James N., advisor; Maloney, Eric D., committee member; Johnson, Richard H., committee member; Chandrasekar, V., committee member; Fairall, Christopher W., committee memberHeating and rain freshening often stabilize the upper tropical ocean, bringing the ocean mixed layer depth to the sea surface. Thin mixed layer depths concentrate subsequent fluxes of heat, momentum, and freshwater in a thin layer. Rapid heating and cooling of the tropical sea surface is important for controlling or triggering atmospheric convection. Ocean mixed layer depth and SST variability due to rainfall events have not been as comprehensively explored as the ocean’s response to heating or momentum fluxes, but are very important to understand in the tropical warm pool where precipitation exceeds evaporation and many climate phenomena such as ENSO and the MJO (Madden Julian Oscillation) originate. The first part of the dissertation investigates tropical, oceanic convective and stratiform rainfall variability and determines how to most accurately estimate rainfall accumulation with radar from each rain type. The second, main part of the dissertation uses central Indian Ocean salinity and temperature microstructure measurements and surrounding radar-derived rainfall maps throughout two DYNAMO MJO events to determine the impact of precipitating systems on upper-ocean mixed layer depth and resulting SST variability. The ocean mixed layer was as shallow as 0-5 m during 528/1071 observation hours throughout 2 MJOs (54% of the data record). Out of 43 observation days, thirty-eight near-surface mixed layer depth events were attributed to freshwater stabilization, called rain-formed mixed layers (RFLs). Thirty other mixed layer stratification events were classified as diurnal warm layers (DWLs) due to stable temperature stratification by daytime heating. RFLs and DWLs were observed to interact in two ways: 1) RFLs fill preexisting DWLs and add to total near-surface mixed layer stratification, which occurred ten times; 2) RFLs last long enough to heat, creating a new DWL on top of the RFL, which happened nine times. These combination stratification events were responsible for the highest SST warming rates and some of the highest SSTs leading up to the most active precipitation and wind stage of the each MJO. DWLs without RFL interaction helped produce the highest SSTs in suppressed MJO conditions. As storm intensity, frequency, duration, and the ability of storms to maintain stratiform rain areas increased, RFLS became more common in the disturbed and active MJO phases. Along with the barrier layer, DWL and RFL stratification events helped suppress wind-mixing, cooling, and mixed layer deepening throughout the MJO. We hypothesize that both salinity and temperature stratification events, and their interactions, are important for controlling SST variability and therefore MJO initiation in the Indian Ocean. Most RFLs were caused by submesoscale and mesoscale convective systems with stratiform rain components and local rain accumulations above 10 mm but with winds mostly below 8 m s-1. We hypothesize that the stratiform rain components of storms helped stratify the ocean by providing weak but widespread, steady, long-lived freshwater fluxes. Although generally limited to rain rates ≤ 10 mm hr-1, it is demonstrated that stratiform rain can exert a strong buoyancy flux into the ocean, i.e. as high as maximum daytime solar heating. Storm morphology and the preexisting vertical structure of ocean stability were critical in determining ocean mixed layer depth variability in the presence of rain. Therefore, we suggest that high spatial and temporal resolution coupled ocean-atmosphere models that can parameterize or resolve storm morphology as well as ocean mixed layer and barrier layer evolution are needed to reproduce the diurnal and intraseasonal SST variability documented throughout the MJO.