Ph.D. - Meteorology

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    Orographic Precipitation Over the Island of Oahu.
    ( 2018-08) Robinson, Thomas E. ; Meteorology
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    Bacterial Coral Pathogens of the Genus Vibrio
    ([Honolulu] : [University of Hawaii at Manoa], [August 2016], 2016-08) Ushijima, Blake
    Coral reefs play an important role in numerous marine ecosystems, however, their survival is threatened by outbreaks of disease. On their own, reefs have the ability to regenerate after destructive events like natural disasters; however recent threats have pushed coral reefs past the point of recovery and many reefs are now under threat of disappearing forever. Outbreaks of diseases specific to corals have already decimated the reefs of the Florida Keys and the Caribbean. In addition, the baseline levels of disease are increasing, as well as the expansion of disease outbreaks into new regions and the broadening of coral species that are affected. Unfortunately, not all of the characterized diseases have a pathogen positively identified and many of the mechanisms of disease for the known pathogens have yet to be determined. This piece of work describes the isolation, identification, and characterization of three virulent Vibrio strains that infect and cause tissue lysis in Hawaiian corals and species at Palmyra Atoll. First, Vibrio oswensii strain OCN002 causes chronic Montipora white syndrome (cMWS) among the Hawaiian Rice coral (Montipora capitata), a major reef building species, in Kāne‘ohe Bay, Hawai‘i. Second, Vibrio coralliilyticus strain OCN008 causes a comparably faster-spreading disease called acute Montipra white syndrome (aMWS). Third, V. coralliilyticus strain OCN014 is a cause of Acropora white syndrome among the table coral (Acopora cytherea) at Palmyra Atoll. In addition to characterizing infection, common virulence factors between the two V. coralliilyticus were investigated and a direct link between rising global sea surface temperatures and increased virulence of a coral pathogen was established. This work also describes the identification of a novel virulence mechanism utilized by strain OCN008, which may represent the evolution of this pathogenic species in response to the protective properties conferred to coral by the microorganisms normally associated with it.
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    Test and Establishment of Using Monocytes and Monocyte-Derived Macrophages as a Novel Therapeutic Delivery System to the Brain
    ([Honolulu] : [University of Hawaii at Manoa], [August 2016], 2016-08) Tong, Hsin-I
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    The Meridional SST Gradient, Low-Level Clouds, and the Latitudinal Location of the ITCZ in the Eastern Pacific: Climatology, Seasonal Cycle, and Interannual Variability
    ([Honolulu] : [University of Hawaii at Manoa], [May 2015], 2015-05) Zhou, Li
    The meridional shift of the Intertropical Convergence Zone (ITCZ) in the eastern Pacific does not completely follow that of the surface convergence or the local maximum SST, especially in cold season and equatorial cold years when the SST front in the eastern tropical Pacific is strong. This study focuses on the physical processes and mechanisms that predominantly control the meridional shifts of the ITCZ in the eastern Pacific based on high resolution satellite observational data and regional atmospheric model simulations. Observational analyses show that the latitudinal location of the ITCZ in the tropical eastern Pacific is highly correlated with the intensity of the SST gradient (SSTG). The SSTG over the sharp SST front is responsible for the formation of a shallow meridional circulation (SMC) from the ITCZ to the cold tongue. The SMC is significant characterized by a returning flow at around 700 hPa from the ITCZ to the cold tongue, descending over the cold tongue with a maximum at around 0-2oN, and a strong near-surface southerly between the cold tongue and the ITCZ. In the ITCZ, the upward branch of the SMC and the typical Hadley circulation are associated two maximums of vertical velocity at the 850 hPa and 300 hPa. The SMC provides moisture to deep convection and thus largely controls the latitudinal location of the ITCZ and its meridional shift. It is evidenced by the stronger SMC in September, associating surface southerly maxima from the SST front near 3oN to the ITCZ, compared with that in June. Meanwhile, low-level clouds form downstream of the SST front under the returning flow of the SMC and just above the maximum surface northward wind. The low-cloud-top radiative cooling increases the meridional pressure gradient between the SST front and the ITCZ and thus enhances the SMC. The stronger meridional SSTG together with the denser low clouds would lead to stronger and more northward ITCZ when SSTG is stronger. Since the SSTG across the eastern Pacific cold tongue displays a strong seasonal cycle, the control of ITCZ convection by the SMC and the related cloud-radiative forcing also experiences a strong seasonal cycle. The SMC is significant year-round except in boreal spring when SSTG weakens. In boreal spring, the SSTG is relatively weak and provides a weak control on the meridional location of the ITCZ, and low-level and high-level clouds are collocated with surface convergence, indicating the dominant control of surface convergence on the ITCZ convection/precipitation. The overlaying of high-level and low-level clouds persists until June when deep convection in the ITCZ is largely affected by the continental monsoon over the Central and North America. The vertical structure of the ITCZ is stronger coupled in boreal summer. In fall when the SSTG is the strongest, the SMC is also the strongest, associated with more northern location of the ITCZ with a large northward vertical tilting from the surface to the upper troposphere. In winter, the ITCZ moves southward when the gap wind from Central America is stronger. The more northward tilted convergence and vertical cloud structure in the ITCZ may be related the tropical waves. In cold seasons when the SSTG is stronger, the meridional gradient of CRF within the atmosphere is amplified due to the increased low-level clouds downstream of the SST front together with the increased middle/high-level clouds in the ITCZ, positively feedback to the SMC and the ITCZ precipitation. The above relations are also applicable in the interannual timescale with more northern location of the ITCZ in the equatorial cold years and vice versa. The relative location changes of the ITCZ to normal years are asymmetrical between El Nino years and La Nina years with larger amplification in El Nino years. The SMC seems more significant in the La Nina events and it is not significant in the El Nino events when the tropical convections are stronger and the SSTG is weaker. iRAM simulations are used to help to understand the physical processes. The iRAM results are evaluated in climatological mean, seasonal, and interannual time scale. It simulated well in these timescale on multiple variables including the latitudinal location of the ITCZ, clouds, SMC, and the CRF. Comparison in the meridional circulation between the ENSO years and Non-ENSO years apparently show the enhanced SMC in the La Nino events. Sensitivity experiments with SSTA cooling or warming are added over the cold tongue to produce different intensity of the SSTG. The analyses of the heating budget show that the low-level cloud radiative cooling and the vertical mixing due to change of the low-level cloud produce similar magnitude as the diabatic heating in the change of the SMC, which contribute the northward or southward shift of the ITCZ.
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    Formation of Precipitation-Circulation-Sea Surface Temperature Patterns under Global Warming
    ([Honolulu] : [University of Hawaii at Manoa], [May 2015], 2015-05) Zhang, Lei
    Most of CMIP5 models projected a weakened Walker Circulation and an El Nino like warming in the tropical Pacific, but what causes such a change is still an open question. We hypothesize that the following three mechanisms are responsible. The first mechanism is a so called “longwave radiative – evaporative damping” mechanism. A simple analytical model was constructed to understand the formation mechanisms of future SST warming pattern under global warming. It is demonstrated that the future SST warming pattern is primarily determined by present-day mean SST and surface latent heat flux (𝑄#$) fields through a longwave radiative – evaporative damping mechanism. Assume a local thermodynamic equilibrium limit without circulation and cloud changes, a uniform GHG forcing would lead to a smaller (larger) warming in the regions where mean SST and 𝑄#$ are large (small). This longwave radiative – evaporative damping mechanism can explain a much greater warming in high latitudes than in tropics, and an El Nino like warming in tropical Pacific. In addition, cloud decreases (increases) in eastern (central) Pacific due to weakened Walker circulation (warmer SST), which also contributes to the El Nino like warming. The second mechanism is “the richest get richer”. In response to a uniform surface warming, the Asia-western North Pacific (WNP) monsoon system is enhanced by competing moisture with other large-scale ascending systems. The strengthened WNP monsoon induces surface westerlies in the western-central equatorial Pacific, weakening the Walker circulation. Idealized AGCM experiments that separate the effect of the mean warming and the relative SST warming pattern clearly demonstrate the effect of the mean warming on change of the equatorial wind. The third mechanism is extra land surface warming, that is, the land obtains a larger warming than the ocean. In particular, a great thermal contrast between American continent and tropical Pacific causes a zonal pressure gradient and westerly anomalies in the eastern equatorial Pacific. This weakens the Walker circulation. A traditional view of weakened Walker circulation is attributed to a slower increase rate of global mean precipitation than moisture. However, by analyzing a uniform warming experiment in an aqua-planet setting, it is demonstrated that the Walker circulation is strengthened, even though global averaged upward motion is weakened. This result suggests that the global moisture budget argument may not be sufficient to explain the change of the Walker circulation in the tropics. By conducting numerical simulations in a realistic land-ocean distribution, we demonstrated that the weakening of the Walker Circulation is attributed to both the monsoon and land forcing effects. The relative SST warming pattern also plays a role, but it is just an amplifier, not a fundamental cause.
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    El Niño/Annual Cycle Combination Mode Dynamics
    ([Honolulu] : [University of Hawaii at Manoa], [May 2015], 2015-05) Stuecker, Malte-Fabian
    The intricate interaction between the El Ni~no-Southern Oscillation (ENSO) and the annual cycle has been a long-standing problem in climate science. Here I demonstrate that the nonlinear atmospheric interaction between the Western Pacific warm pool seasonal cycle and ENSO creates a previously overlooked mode of Indo-Pacific climate variability. This combination mode (C-mode) is characterized by near-annual and sub-annual timescales (combination tones) and contributes substantially to the observed low-level atmospheric circulation and precipitation anomalies. The meridionally anti-symmetric warm pool annual cycle is the cause for the characteristic meridionally anti-symmetric C-mode response, while the linear ENSO response is quasi-symmetric with regard to the equator. Several climate phenomena are shown to be manifestations of the C-mode: (i) zonal South Pacific Convergence Zone (SPCZ) events, (ii) the southward shift of anomalous westerlies at the end of the calendar year during El Ni~no events, (iii) the anomalous low-level Northwest Pacific Anticyclone (NWP-AC), and (iv) prolonged low sea-level events in the Southwest Paci c (El Ni~no Taimasa). The NWP-AC bridges the impacts of ENSO to the Asian Monsoon system. Previous research highlighted the importance of thermodynamic air-sea coupling for the genesis and persistence of the NWP-AC. However, I show that the phase transition information for the anomalous Northwest Pacific circulation originates solely from the atmospheric C-mode. Air-sea coupling only contributes amplification and persistence to the C-mode response. The ENSO/annual cycle interaction outlined here can be elegantly viewed as a frequency cascade, which transfers power from the interannual band to higher frequencies (combination tones). This extended ENSO response is not only characterized by different timescales but also by unique circulation and rainfall patterns. Importantly, this high frequency climate variability is purely deterministic in its nature and hence as potentially predictable as ENSO and the seasonal cycle themselves. Finally, the frequency cascade and combination mode frameworks are universal concepts that can be used to understand many nonlinear interactions between different timescale phenomena in the climate system and dynamical systems in general.
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    Water Quality Influences on Declining Coral Settlement from the Great Barrier Reef Region: Biofilms as Key Players
    ([Honolulu] : [University of Hawaii at Manoa], [May 2015], 2015-05) Prescott, Rebecca
    Biofilms (surface attached microbial communities in mucus) are common in coastal marine ecosystems but among the least studied. Their pivotal roles in the resilience of coral reefs stem from their interactions with coral larvae that must select permanent sites for attachment before metamorphosing into coral polyps, a process which can be disrupted by local watershed disturbances. In the laboratory, biofilm communities were exposed to moderately turbid water (50 mg/L sediment) and a doubling of particulate organic matter (POM). Acropora millepora and Pocillopora acuta coral larvae that were provided biofilms from each treatment settled less on those that had been exposed to sediments and organic matter. Pyrosequenced 16S and 18S rRNA gene fragments and scanning electron microscopy showed how community changes in the biofilms in each treatment related to settlement of both coral species’ larvae. We concluded that: 1) particulate carbon levels explained more variation in the community composition of biofilms and in coral settlement response than did turbidity changes; 2) community composition of the microbial eukaryote community shifts from diatom to fungal-dominated; 3) spatial distribution of settlement is driven more by negative cues from biofilms than it is by positive cues; 4) the complex, three dimensional structure of biofilm surfaces diminishes with increased POM and turbidity. Phaeobacter spp. affiliated sequences dominated biofilms before and after treatments. These and other Rhodobacteraceae affiliated sequences were positively associated with A. millepora settlement, but not with that of P. acuta. Phaeobacter spp. occur globally in biofilm communities, produce antibiotics, stimulate algal growth and then produce algaecides to digest algae as it ages, and decrease epibiont settlement on some algae. They may provide key functional roles in coral reef biofilms.
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    Interactions between Aerosol and Marine Stratocumuli Over the South East Pacific
    ([Honolulu] : [University of Hawaii at Manoa], [May 2015], 2015-05) Freitag, Steffen
    During the VOCALS Regional Experiment in 2008 fourteen research flights were conducted over the South East Pacific (SEP) to study the interaction between aerosol and cloud covering a wide range of conditions from a more polluted coastal troposphere to the remote marine environment. Size-resolved aerosol physiochemistry was measured above and below stratocumulus (Sc) clouds along with in-cloud observations of cloud droplet size spectra. Because the nature and variability of aerosol effective as cloud condensation nuclei (CCN) impact cloud microphysical properties through cloud droplet number concentration (Nd), size-resolved aerosol measurements were utilized to establish air mass characteristics and their CCN activity over the SEP. The aerosol number size distribution measurements were clustered into groups using a simple k-means technique that recognizes similar pattern over the aerosol size range assessed. This cluster technique yields four distinct aerosol size distributions for the free troposphere (FT). These are attributed to two local coastal pollution sources and long-range transport of aerosol from the South Pacific and Australia based upon back trajectory analysis and investigation of aerosol physiochemistry. Marine boundary layer (MBL) observations reveal six distinct clusters associated with different stages of aging and processing of coastal combustion sources, clean South Pacific and heavy drizzling air masses. All air masses show CCN activity is strongly dependent on aerosol number concentration and size distribution shape, while aerosol hygroscopicity plays a smaller role. This confirms earlier studies although observed MBL hygroscopicity considerably exceeds the previously recommended value of 0.7. Derived MBL CCN also reveal a 1:1 relationship to Nd over the range of air mass characteristics observed once droplet concentrations are corrected for instrumental artifacts that tend to undercount Nd in polluted clouds. This is contrary to some previous estimates of aerosol-cloud interaction and could result in changes in local cloud radiative forcing of -3 to -10 W m−2. In-cloud measurements from VOCALS campaign also show a robust dependency of Nd with the empirical correction factor k∗ utilized in cloud radiative transfer codes in climate models to account for droplet spectral properties. This relationship can be traced to aerosol size distributions below the clouds. Measurements for both clean marine and pollution influenced aerosol populations indicate that as they undergo cloud processing, reducing the number of CCN and Nd, their droplet mean radius (rµ) increases while spectrum width (rσ ) is unaffected. The associated k∗ increases, as it is roughly proportional to rµ / rσ . If this dependency is not accounted for, local forcing could be overestimated by 3 to 6 W m−2 in polluted clouds close to the Chilean coastline. In-cloud measurements also showed that the highest drizzle rates occur in the absence of typical pollution indicators as carbon monoxide and black carbon.
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    A comparison of two heavy rainfall events and impacts of data assimilation on a coastal heavy rainfall event during TiMREX (2008)
    ([Honolulu] : [University of Hawaii at Manoa], [December 2013], 2013-12) Tu, Chuan-Chi
    Two contrasting localized heavy rainfall events during Taiwan's early summer rainy season with the daily rainfall maximum along the windward mountain range and coast were studied and compared using a combination of observations and numerical simulations. Both events occurred under favorable large-scale settings including the existence of a moisture tongue from the tropics. For the 31 May case, heavy rainfall occurred in the afternoon hours over the southwestern windward slopes after a shallow surface front passed central Taiwan. The orographic lifting of the prevailing warm, moist, west-southwesterly flow aloft, combined with a sea breeze-upslope flow at the surface provided the localized lifting needed for the development of heavy precipitation. On 16 June before sunrise, pronounced orographic blocking of the warm, moist, south/southwesterly flow occurred because of the presence of relatively cold air at low levels with an offshore wind component as a result of nocturnal and rain evaporative cooling. This also caused convective systems to intensify as they moved toward the southwestern coast. During the daytime, the cold pool remained over southwestern Taiwan without the development of onshore/upslope flow. Furthermore, with a southsouthwesterly flow aloft parallel to terrain contours, orographic lifting was almost absent, and pre-existing rain cells offshore diminished after they moved inland. Over northern Taiwan on the leeside, a sea-breeze/onshore flow developed in the afternoon hours, resulting in heavy thundershowers. Our results demonstrate the importance of diurnal and local effects on determining the location and timing for the occurrences of localized heavy precipitation during the early summer rainy season over Taiwan. Constellation Observing System for Meteorology, Ionosphere, and Climate global positioning system (GPS) radio-occultation (RO) soundings were used to depict the prefrontal moist tongue for a heavy rainfall case (16 June 2008) during the early summer season over Taiwan. Cycling model runs assimilate Terrain-influenced Monsoon Rainfall Experiment (TiMREX) data, global telecommunications system (GTS) data and GPS RO sounding data in order to improve the initial conditions for the outermost domain as well as all nested domains. This leads to better representations of the prefrontal moist tongue over the open ocean, a weak 500-hPa prefrontal trough, and the modifications of the planetary boundary layer structure by the antecedent rains of 14-15 June. The GPS RO data have positive impacts on subsynoptic features including the upper-level low/trough location and orientation resulting in a better initial condition for sequence forecast for upward motion and rainfall patterns. The initial air temperature in the boundary layer over southwestern Taiwan in the early morning of 16 June is relatively cold with significant orographic blocking as compared with the control run initialized with the National Centers for Environmental Prediction (NCEP) Global Forecast System (GFS) data. As a result, local circulations over Taiwan as well as rainfall along the southwestern coast and afternoon heavy showers in the wake zone over northern Taiwan are better predicted with cycling runs that start 36 hours before the model forecasts.