acase@tulane.edu

acase@tulane.edu

The movement of tropical cyclones (TC) is studied numerically based on a two-dimensional barotropic model, using a previously developed non-oscillatory balanced scheme. The model of TC used here takes an exponential form, and its size and strength are selected to be of a middle scale. Without a background flow, TCs move in the northwest direction due to the beta effect. The amplitudes of high wavenumber modes of the asymmetric flow, that are believed to be responsible for the TC drift, are computed using Fourier analysis. The amplitude of wavenumber one and two modes are dominant, so they are indicators of beta conversion of energy. Also, the effect of the monsoon trough on the TC movement is investigated. The results show a sudden change of the TC propagation path, consistent with earlier work. These two studies correspond to previous works. Here, the effect of equatorially trapped waves such as Kelvin, Rossby, and Mixed Rossby Gravity, on the TC path is newly studied by varying the wavenumber and wave speed of the underlying waves. The effect of the waves is considered because they are believed to contribute to cyclogenesis. For studying the effect, the barotropic flow induced by these waves via momentum transport and its variation were simulated for 50 days, and some patterns are found in the change of maximum wind speed. At a given time during the simulation, a TC is injected and the effect of the background wave is analyzed. Using the wavefield of 11 cases from 10 days to 30 days, the trajectories are calculated, and their patterns appear to be stochastic. So, the patterns are identified by calculating the mean path and its spread. The trajectories of TCs are different for different time of the waves. Kelvin waves make small variations on the length and direction of the trajectory of TCs. On the contrary, Rossby waves cause a dramatic change in the TC path and yield longer trajectories. Meanwhile, TCs in MRG waves keep fairly the same direction and usually have longer traveling distance. These changes vary by wave conditions. Therefore, the three kinds of waves have different effects on the trajectories of the TC. For some peculiar cases, the movements are explained based on wavefields. / Graduate

Farmers in the developing world frequently find themselves in uncertain and risky environments: often having to make decisions based on very little information. Functional models are needed to support farmers tactical decisions. In order to develop an appropriate model, a comparison is carried out of potential modelling approaches to address the question of what to grow where. A probabilistic GlS model is identified in this research as a suitable model for this purpose. This model is implemented as the stand-alone Spatial Decision Support System (SDSS) CaNaSTA, based on trial data and expert knowledge available for Central America and forage crops. The processes and methods used address many of the problems encountered with other agricultural DSS and SDSS. CaNaSTA shows significant overlap with recommendations from other sources. In addition, CaNaSTA provides details on the likely adaptation distribution of each species at each location, as well as measures of sensitivity and certainty. The combination of data and expert knowledge in a spatial environment allows spatial and aspatial uncertainty to be explicitly modelled. This is an original approach to the problem of helping farmers decide what to plant where.

The vertical structures of tropospheric temperature and moisture over the oceans have not been well observed to date. The Atmospheric Infrared Sounder (AIRS) aboard NASA?s Aqua satellite offers the opportunity to provide observed soundings of these variables. This thesis focuses on the validation and application of AIRS soundings in the tropical troposphere over the Atlantic Ocean, with emphasis on the Saharan Air Layer (SAL). SAL outbreaks occur every few days, producing a warm air mass that is particularly dry at the middle levels. These westward-propagating plumes inhibit convection and are thereby thought to possess a detrimental effect on African easterly waves and tropical cyclones (TCs). First, AIRS soundings are compared with concurrent Global Positioning System (GPS) dropwindsonde data released from NOAA?s Gulfstream-IV jet aircraft, for three TC cases. In SAL environments, temperature soundings from both instruments are usually consistent. Additionally, AIRS is able to capture the very dry air in the middle levels, but it generally underestimates the moisture in the boundary layer and often misses the sharp vertical moisture gradient at the SAL base (~850 hPa). In the moist tropical boundary layer, AIRS also exhibits a dry bias. Cloud cover also prevents AIRS from accurately sampling the low-level moisture. Next, total precipitable water is derived from AIRS soundings and averaged over daily, monthly and seasonal timescales. The significant monthly and interannual variability of the moisture distribution is found to be consistent with expectations. A peak in the probability density function of mixing ratio corresponding to dry air is observed in the lower-mid troposphere in early summer, consistent with the increased frequency of SAL outbreaks during this period. Finally, the relationship between dry air derived from AIRS and TC intensity is explored. As the amount of dry air increases, particularly in the southeast and northeast quadrants of the TC, the TC becomes more likely to weaken. In the presence of high wind shear or low sea surface temperature, the likelihood of weakening increases further. While these results highlight some shortcomings of the AIRS data, their importance and uniqueness are emphasized via new applications of AIRS soundings over data sparse regions.

This thesis seeks to identify locations in which errors in numerical model initial conditions may compromise skill in tropical cyclone (TC) track forecasts. Two major TCs that made landfall in 2008 are analyzed: Hurricane Ike and Typhoon Sinlaku. In order to examine the sensitivity of the TC to selected synoptic features, a vorticity perturbation technique is developed. Within a chosen radius and atmospheric depth, the vorticity is amplified or decreased, followed by a re-balancing of the fields. The following questions are proposed: (1) How does the TC track vary with respect to initial perturbations of differing amplitude, spatial scale and distance to the storm? (2) How does the evolving perturbation act to modify the synoptic environment surrounding the TC, and thereby the track? (3) Is it best to follow an objective technique to determine the sensitive areas, or is it better to use a subjective method based on fundamental synoptic reasoning? Utilizing the Weather Research and Forecasting (WRF) model, the ?control? simulation for each TC is found to replicate forecast errors evident in the operational global models. For Sinlaku, this includes a premature recurvature in the forecast. For Ike, this comprises a landfall too far south along the Texas coast due to no recurvature being forecast. The size, magnitude and location of vorticity perturbations to the control analysis are chosen subjectively. For Sinlaku, these locations include a large mid-latitude shortwave trough around 3000 km to the north-northwest, a smaller upper-level shortwave immediately to the north, a low-level monsoon trough to the west-southwest, a weak tropical storm to the northeast, and a local perturbation in the immediate environment. It is found that WRF forecasts of Sinlaku exhibit high sensitivity, with large modifications to its track arising from the perturbation of each selected targets in the synoptic environment. The greatest improvement in the track forecast occurs by weakening the vorticity associated with each of two shortwaves to the north of Sinlaku, suggesting that either or both of the shortwaves may have been initialized too strongly in the model analysis, thereby contributing to an erroneous recurvature. For Ike, the perturbation locations include a large mid-latitude shortwave trough 2500 km to its north, an upper-level cutoff low to the east-northeast, a low-level shortwave trough to the northwest, a tropical storm in the East Pacific, and a local perturbation in the immediate environment. In contrast to Sinlaku, the perturbation of synoptic targets around Ike produces less sensitivity, likely due to the fact that Ike is not in a position of imminent recurvature. The only perturbation that leads to an accurate 4-day forecast of recurvature and landfall in North Texas is the strengthening of the large mid-latitude shortwave trough, suggesting that the shortwave may have been initialized too weakly in the operational models. Finally, a comparison of targets selected objectively by the Ensemble Transform Kalman Filter (ETKF) versus the above subjectively-chosen targets suggests that while the ETKF effectively indicates similar target regions to those selected subjectively, it may be less effective in ranking the relative sensitivities of those targets. Overall, it is found that the TC track is more sensitive to perturbations of larger amplitude and spatial scale, and less so to the distance between the perturbation and the TC, and sensitivity is confined to specific regions of the flow. The perturbation methodology employed here may be used to offer suggestions of locations in which extra high-density satellite data may be assimilated.

A mesoscale tropical channel model is constructed to study the long-standing problem of the initiation of the Madden-Julian Oscillation (MJO). Two observed cases of MJO are chosen, one in boreal spring and one in boreal winter, without a priori knowledge of their initiation mechanism. With initial and lateral boundary conditions provided by a global reanalysis, this model is able to reproduce the initiation and gross features of two observed MJO events up to two months after the start of simulations. This leads to a conjecture that these two MJO events are generated by the influences from the lateral boundaries. This conjecture is supported by a series of sensitivity tests. These sensitivity tests demonstrate that the simulated MJO initiation does not critically depend on detailed characteristics of sea surface temperature (varying vs. constant in time, mean distribution from boreal spring vs. winter), initial conditions (within a 10 day period, perturbations in the initial conditions), the latitudinal location of the lateral boundaries (21 - 45˚N and S), and even latent heating and moist processes. The only factor found critical to the reproduction of the MJO initiation is time varying lateral boundary conditions from the reanalysis. When such lateral boundary conditions are replaced by time independent conditions, the model fails to reproduce the MJO initiation. The analysis of moist static energy has revealed that the discharge-recharge mechanism is not sufficient for the MJO initiation in the model. It is found that the latitudinal transport of westerly momentum from the extratropics is crucial in generating the lower tropospheric westerlies in the reanalysis and model. The energy source for the extratropical perturbation is through extraction of kinetic energy from the mean flow. The estimation of wave activity flux has revealed that there is a major region over the southern Indian Ocean, which produces wave activity flux towards the tropical genesis region of the MJO initiation. We have also investigated the time-scale of the boundary conditions that are responsible for the MJO initiation. Additions of small perturbations in the boundary conditions, and use of 10-day interpolated boundary conditions do not affect the MJO initiation. Thus boundary conditions responsible for the MJO initiation in the model must have time scales greater than 10 days, indicating that the shorter time scale stochastic forcing through the lateral boundaries did not play any major role. The estimation of the zonal momentum budget for the MJO initiation region has revealed the importance of the advective terms, particularly by the meridional winds before the onset of the MJO. The importance of the extratropical influences in initiating the MJO in the channel model leads to a speculation that a multi-year simulation using a tropical channel model would also produce reasonable MJO statistics if forced by time varying boundary conditions. Interestingly, the MJO statistics in the multi-year simulation using a tropical channel model is found to be not better than the global models. Increase of horizontal resolution and use of a different cumulus scheme did not improve the MJO simulation. We found that the error in the mean state was the main reason for the lack of MJO statistics in the model. The model took less than five days for the error to reach its climate bias. Thus, a good simulation of the mean state is important for the successful simulation of the MJO. Implications of these results are discussed. In short, this study has shown that the extratropical influences can be an efficient mechanism for the MJO initiation and calls for further research attention to this mechanism that has been somewhat neglected by mainstream MJO research.

Tropical cyclone (TC) intensity change is governed by internal dynamics (e.g. eyewall contraction, eyewall replacement cycles, interactions of the inner-core with the rainbands) and environmental conditions (e.g. vertical wind shear, moisture distribution, and surface properties). This study aims to gain a better understanding of the physical mechanisms responsible for TC intensity changes with a particular focus to those related to the vertical wind shear and surface properties by using high resolution, full physics numerical simulations. First, the effects of the vertical wind shear on a rapidly intensifying storm and its subsequent weakening are examined. Second, a fully coupled atmosphere-wave-ocean model with a sea spray parameterization is used to study the impact of sea spray on the hurricane boundary layer. The coupled model consists of three components: the high resolution, non-hydrostatic, fifth generation Pennsylvania State University-NCAR mesoscale model (MM5), the NOAA/NCEPWAVEWATCH III (WW3) ocean surface wave model, and theWHOI threedimensional upper ocean circulation model (3DPWP). Sea spray parameterizations were developed at NOAA/ESRL and modified by the author to be introduced in uncoupled and coupled simulations. The model simulations are conducted in both uncoupled and coupled modes to isolate various physical processes influencing TC intensity. The very high-resolutionMM5 simulation of Hurricane Lili (at 0.5 km grid resolution) showed a rapid intensification associated with a contracting eyewall. Changes in both the magnitude and the direction of the vertical wind shear associated with an approaching upper-tropospheric trough were responsible for the weakening of the storm before landfall. Hurricane Lili weakened in a 5-10 m/s vertical wind shear environment. The simulated storm experienced wind shear direction normal to the storm motion, which produced a strong wavenumber one rainfall asymmetry in the downshear-left quadrant of the storm. The rainfall asymmetry was confirmed by various observations from the TRMM satellite and the WSR-88D ground radar in the coastal region. The increasing vertical wind shear induced a vertical tilt of the vortex with a time lag of about 5-6 hours after the wavenumber one rainfall asymmetry was first observed in the model simulation. Other key factors controlling intensity and intensity change in tropical cyclones are the air-sea fluxes. Accurate measurement and parameterization of air-sea fluxes under hurricane conditions are challenging. Although recent studies have shown that the momentum exchange coefficient levels off at high wind speed, little is known about the high wind behavior of the exchange coefficient for enthalpy flux. One of the largest uncertainties is the potential impact of sea spray. The current sea spray parameterizations are closely tied to wind speed and tend to overestimate the mediated heat fluxes by sea spray in the hurricane boundary layer. The sea spray generation depends not only on the wind speed but also on the variable wave state. A new spray parameterization based on the surface wave energy dissipation is introduced in the coupled model. In the coupled simulations, the wave energy dissipation is used to quantify the amount of wave breaking related to the generation of sea spray. The spray parameterization coupled to the waves may be an improvement compared to sea spray parameterizations that depends on wind speed only.

El presente trabajo de investigación se realizó sobre la inquietud que se tenía referente a las diferentes opiniones con relación a los aspectos cualitativos del recurso humano de los servicios de la salud, ya que estos han sido dejados de lado en el sistema, considerando al trabajador en salud como un objeto de trabajo que solo debía cumplir ciertos requisitos para ocupar un cargo y desempeñarse de acuerdo a normas, procedimientos ya establecidos, en busca del logro de metas cuantificadas estadísticamente: no se consideró al recurso humano como al sujeto primordial de la organización y que sus percepciones, comportamientos y participación dentro de ella, están ligados con la producción y calidad del servicio

binding of either tyrosine or 6MPH4 alone does not change the coordination. However, when both tyrosine and 6MPH4 are bound, the active site becomes 5-coordinate, creating an open site for reaction with O2. Investigation of the kinetics of oxygen reactivity of TyrH complexes in the absence and presence of tyrosine and/or 6MPH4 indicated that there is a significant enhancement in reactivity in the 5-coordinate complex in comparison to the 6-coordinate form. Similar investigations with E332A TyrH showed that Glu332 residue plays a role in directing the protonation of the bridged complex that forms prior to the formation of Fe(IV)O. Rapid chemical quench analyses of DOPA formation showed a burst of product formation, suggesting a slow product release step. Steady-state viscosity experiments established a diffusional step as being significantly rate-limiting. Further studies with stopped-flow spectroscopy indicated that the rate of TyrH reaction is determined by a combination of a number of physical and chemical steps. Investigation of the NO complexes of TyrH by means of optical absorption, electron paramagnetic resonance (EPR) and electron spin echo envelope modulation (ESEEM) techniques revealed the relative positions of the substrate and cofactor with respect to NO, an O2 mimic, and provided further insight into how the active site is tuned for catalytic reactivity upon substrate and cofactor binding. The second theory is that a decreased vertical temperature lapse rate, dT/dp, would slow cloud growth, creating a mode of cloud-top heights at the stable layer as clouds lose buoyancy. The signal for lapse rate changes in the AIRS data, however, is not as strong as the signal for RH differences. Near 600-400 hPa, roughly the region where congestus cloud-top heights are located, no significant difference in lapse rates is noted between congestus and deep clouds; in fact, the mean values suggest that congestus clouds appear in more unstable atmospheres than deep clouds. Only slight differences in temperature and lapse rate are noted in ERA data as well. These results suggest that drier air may play a greater role in limiting congestus cloud-top heights than increased atmospheric stability. Five years of relative humidity (RH) observations from the Atmospheric Infrared Sounder (AIRS) instrument aboard the Aqua satellite are then analyzed to identify areas of anomalously dry air between 600 and 400 hPa over deep convective regions of the tropical oceans. Back trajectories are then calculated for each observed parcel.