Statistical Deterministic and Ensemble Seasonal Prediction of Tropical Cyclones in the Northwest Australian Region

Statistical seasonal prediction of tropical cyclones (TCs) has been ongoing for quite some time in many different ocean basins across the world. While a few basins (e.g., North Atlantic and western North Pacific) have been extensively studied and forecasted for many years, Southern Hemispheric TCs have been less frequently studied and generally grouped as a whole or into two primary basins: southern Indian Ocean and Australian. This paper investigates the predictability of TCs in the northwest Australian (NWAUS) basin of the southeast Indian Ocean (105°–135°E) and describes two statistical approaches to the seasonal prediction of TC frequency, TC days, and accumulated cyclone energy (ACE). The first approach is a traditional deterministic seasonal prediction using predictors identified from NCEP–NCAR reanalysis fields using multiple linear regression. The second is a 100-member statistical ensemble approach with the same predictors as the deterministic model but with a resampling of the dataset with replacement and smearing input values to generate slightly different coefficients in the multiple linear regression prediction equations. Both the deterministic and ensemble schemes provide valuable forecasts that are better than climatological forecasts. The ensemble approach outperforms the deterministic model as well as adding quantitative uncertainty that reflects the predictability of a given TC season

Statistical Deterministic and Ensemble Seasonal Prediction of Tropical Cyclones in the Northwest Australian Region

Statistical seasonal prediction of tropical cyclones (TCs) has been ongoing for quite some time in many different ocean basins across the world. While a few basins (e.g., North Atlantic and western North Pacific) have been extensively studied and forecasted for many years, Southern Hemispheric TCs have been less frequently studied and generally grouped as a whole or into two primary basins: southern Indian Ocean and Australian. This paper investigates the predictability of TCs in the northwest Australian (NWAUS) basin of the southeast Indian Ocean (105°–135°E) and describes two statistical approaches to the seasonal prediction of TC frequency, TC days, and accumulated cyclone energy (ACE). The first approach is a traditional deterministic seasonal prediction using predictors identified from NCEP–NCAR reanalysis fields using multiple linear regression. The second is a 100-member statistical ensemble approach with the same predictors as the deterministic model but with a resampling of the dataset with replacement and smearing input values to generate slightly different coefficients in the multiple linear regression prediction equations. Both the deterministic and ensemble schemes provide valuable forecasts that are better than climatological forecasts. The ensemble approach outperforms the deterministic model as well as adding quantitative uncertainty that reflects the predictability of a given TC season

Interannual Variability of Northwest Australian Tropical Cyclones

Tropical cyclone (TC) activity over the southeast Indian Ocean has been studied far less than other TC basins, such as the North Atlantic and northwest Pacific. The authors examine the interannual TC variability of the northwest Australian (NWAUS) subbasin (0 degrees-35 degrees S, 105 degrees-135 degrees E), using an Australian TC dataset for the 39-yr period of 1970-2008. Thirteen TC metrics are assessed, with emphasis on annual TC frequencies and total TC days. Major findings are that for the NWAUS subbasin, there are annual means of 5.6 TCs and 42.4 TC days, with corresponding small standard deviations of 2.3 storms and 20.0 days. For intense TCs (WMO category 3 and higher), the annual mean TC frequency is 3.0, with a standard deviation of 1.6, and the annual average intense TC days is 7.6 days, with a standard deviation of 4.5 days. There are no significant linear trends in either mean annual TC frequencies or TC days. Notably, all 13 variability metrics show no trends over the 39-yr period and are less dependent upon standard El Nino-Southern Oscillation (ENSO) variables than many other TC basins, including the rest of the Australian region basin. The largest correlations with TC frequency were geopotential heights for June-August at 925 hPa over the South Atlantic Ocean (r = -0.65) and for April-June at 700 hPa over North America (-0.64). For TC days the largest correlations are geopotential heights for July-September at 1000 hPa over the South Atlantic Ocean (-0.7) and for April-June at 850 hPa over North America (-0.58). Last, wavelet analyses of annual TC frequencies and TC days reveal periodicities at ENSO and decadal time scales. However, the TC dataset is too short for conclusive evidence of multidecadal periodicities. Given the large correlations revealed by this study, developing and testing of a multivariate seasonal TC prediction scheme has commenced, with lead times up to 6 months

Computational studies of the catalytic reactions of group ivb and vib transition metal oxide clusters

Computational chemistry approaches have been used to study the reactivity of Group IVB and VIB transition metal oxide clusters. The hydrolysis of MCl4 (M = Zr, Hf) as the initial steps on the way to form zirconia and hafnia nanoparticles has been studied with density functional theory (DFT) and coupled cluster [CCSD(T)]theory. Instead of the direct production of MOCl2 and HCl or MO2 and HCl, the hydrolysis reaction starts with the formation of oxychlorohydroxides followed by the release of HCl due to the large endothermicities associated with the direct path to form gas phase MO2. The formation of MO2 nanoparticles by the high temperature oxidation method is complicated and is associated with the potential production of a wide range of intermediates. The interaction between H2O and small (MO2)n (M = Ti, Zr, Hf, n = 1−4) nanoclusters has been studied for the first step to understand the reaction mechanism of photocatalytic water splitting with the presence of (MO2)n as catalysts. Both the singlet and the first excited potential energy surfaces (PESs) are studied. The hydrolysis reactions begin with the formation Lewis acid-base adducts followed by proton transfer from H2O to the nanclusters. The reactions are highly exothermic with very small activation energies. Thus, H2O should readily decompose to generate two OH groups on (MO2)n nanoclusters. The generation of H2 and O2 starting from the hydroxides formed in the hydrolysis step has been studied with the same computational methods as used for the hydrolysis study. The water splitting reactions prefer to take place on the first excited triplet potential energy surface (PES) due to its requirement of less energy than that on the singlet PES. A low excess potential energy is needed to generate 2H2 and O2 from 2H2O if the endothermicity of the reaction is overcome on the first excited triplet PES using two visible photons. Hydrogen generation occurs via the formation of an M−H containing intermediate and this step can be considered to be a proton coupled, electron transfer (PCET) reactions with one or two electrons being transferred. Oxygen is produced by breaking two weak M−O bonds on the triplet PES. Ethanol (CH3CH2OD) conversions on cyclic (MO3)3 (M = Mo, W) clusters have been studied experimentally with temperature programmed desorption and computationally with both DFT and CCSD(T) methods. The addition of two alcohol molecules is required to match experiment. The reaction begins with the elimination of water with the formation of an intermediate of dialkoxy species for further reaction. The dehydration reaction proceeds through a β hydrogen transfer to a terminal MVI = O atom without the involvement of a redox process. The dehydrogenation reaction is through an α hydrogen transfer to an MoVI = O with redox involved or a WVI avoiding redox. The same computational methods have been used to study the other alcohol species such as methanol, n-propanol and isopropanol. The reactions with single, double and triple alcohols per M3O9 cluster have been studied. The dehydrogenation and dehydration for single alcohol reactions is via a common intermediate of metal hydroalkoxide formed by the dissociation of alcohol. The dehydration is through a β hydrogen transfer to OH group. The lowest energy pathway for dehydrogenation is the same for different alcohols in both single and double alcohol reactions. Three alcohols involved condensation reaction may lower the reaction barrier tremendously by the sacrifice of an alcohol to form a metal hydroalkoxide, a strong gas phase Brønsted acid. This is a Brønsted acid driven reaction different from dehydrogenation and dehydration reactions governed by the Lewis acidity of the metal center and its reducibility. (Published By University of Alabama Libraries