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e-Journal

 

An Overview and Brief History of Southern Hemisphere Tropical Cyclones
(Released June 2012)

 
  by Adam Arnold  

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News Articles

  1. A Global View of Equatorial Waves and Tropical Cyclogenesis

    Schreck, Carl J; Molinari, John; Aiyyer, Anantha, Monthly Weather Review, 03-01-2012

    This study investigates the number of tropical cyclone formations that can be attributed to the enhanced convection from equatorial waves within each basin. Tropical depression (TD)-type disturbances (i.e., easterly waves) were the primary tropical cyclone precursors over the Northern Hemisphere basins, particularly the eastern North Pacific and the Atlantic. In the Southern Hemisphere, however, the number of storms attributed to TD-type disturbances and equatorial Rossby waves were roughly equivalent. Equatorward of 20°N, tropical cyclones formed without any equatorial wave precursor most often over the eastern North Pacific and least often over the western North Pacific.

    The Madden-Julian oscillation (MJO) was an important tropical cyclone precursor over the north Indian, south Indian, and western North Pacific basins. The MJO also affected tropical cyclogenesis by modulating the amplitudes of higher-frequency waves. Each wave type reached the attribution threshold 1.5 times more often, and tropical cyclogenesis was 3 times more likely, within positive MJO-filtered rainfall anomalies than within negative anomalies. The greatest MJO modulation was observed for storms attributed to Kelvin waves over the north Indian Ocean.

    The large rainfall rates associated with tropical cyclones can alter equatorial wave-filtered anomalies. This study quantifies the contamination over each basin. Tropical cyclones contributed more than 20% of the filtered variance for each wave type over large potions of every basin except the South Pacific. The largest contamination, exceeding 60%, occurred for the TD band near the Philippines. To mitigate the contamination, the tropical cyclone-related anomalies were removed before filtering in this study.

    For full-text documents see ProQuest's eLibrary

  2. Tropical Cyclone Count Forecasting Using a Dynamical Seasonal Prediction System: Sensitivity to Improved Ocean Initialization

    Alessandri, Andrea; Borrelli, Andrea; Gualdi, Silvio; Scoccimarro, Enrico; Masina, Simona, Journal of Climate, 06-15-2011

    This study investigates the predictability of tropical cyclone (TC) seasonal count anomalies using the Centro Euro-Mediterraneo per i Cambiamenti Climatici-Istituto Nazionale di Geofisica e Vulcanologia (CMCC-INGV) Seasonal Prediction System (SPS). To this aim, nine-member ensemble forecasts for the period 1992-2001 for two starting dates per year were performed. The skill in reproducing the observed TC counts has been evaluated after the application of a TC location and tracking detection method to the retrospective forecasts. The SPS displays good skill in predicting the observed TC count anomalies, particularly over the tropical Pacific and Atlantic Oceans. The simulated TC activity exhibits realistic geographical distribution and interannual variability, thus indicating that the model is able to reproduce the major basic mechanisms that link the TCs' occurrence with the large-scale circulation. TC count anomalies prediction has been found to be sensitive to the subsurface assimilation in the ocean for initialization. Comparing the results with control simulations performed without assimilated initial conditions, the results indicate that the assimilation significantly improves the prediction of the TC count anomalies over the eastern North Pacific Ocean (ENP) and northern Indian Ocean (NI) during boreal summer. During the austral counterpart, significant progresses over the area surrounding Australia (AUS) and in terms of the probabilistic quality of the predictions also over the southern Indian Ocean (SI) were evidenced. The analysis shows that the improvement in the prediction of anomalous TC counts follows the enhancement in forecasting daily anomalies in sea surface temperature due to subsurface ocean initialization. Furthermore, the skill changes appear to be in part related to forecast differences in convective available potential energy (CAPE) over the ENP and the North Atlantic Ocean (ATL), in wind shear over the NI, and in both CAPE and wind shear over the SI.

    For full-text documents see ProQuest's eLibrary

  3. Mesoscale Simulation of Tropical Cyclones in the South Pacific: Climatology and Interannual Variability

    Jourdain, Nicolas C; Marchesiello, Patrick; Menkes, Christophe E; Lefèvre, Jérome; Vincent, Emmanuel M; Lengaigne, Matthieu; Cha, Journal of Climate, 01-01-2011

    The Weather Research and Forecast model at 1/3° resolution is used to simulate the statistics of tropical cyclone (TC) activity in the present climate of the South Pacific. In addition to the large-scale conditions, the model is shown to reproduce a wide range of mesoscale convective systems. Tropical cyclones grow from the most intense of these systems formed along the South Pacific convergence zone (SPCZ) and sometimes develop into hurricanes. The three-dimensional structure of simulated tropical cyclones is in excellent agreement with dropsondes and satellite observations. The mean seasonal and spatial distributions of TC genesis and occurrence are also in good agreement with the Joint Typhoon Warning Center (JTWC) data. It is noted, however, that the spatial pattern of TC activity is shifted to the northeast because of a similar bias in the environmental forcing. Over the whole genesis area, 8.2 ± 3.5 cyclones are produced seasonally in the model, compared with 6.6 ± 3.0 in the JTWC data. Part of the interannual variability is associated with El Niño-Southern Oscillation (ENSO). ENSO-driven displacement of the SPCZ position produces a dipole pattern of correlation and results in a weaker correlation when the opposing correlations of the dipole are amalgamated over the entire South Pacific region. As a result, environmentally forced variability at the regional scale is relatively weak, that is, of comparable order to stochastic variability (±1.7 cyclones yr -1), which is estimated from a 10-yr climatological simulation. Stochastic variability appears essentially related to mesoscale interactions, which also affect TC tracks and the resulting occurrence.

    For full-text documents see ProQuest's eLibrary

Historical Newspapers
  1. A PERILOUS PORT.; WHAT NAVAL OFFICERS SAY OF APIA'S HARBOR. Little Better Than an Open Roadstead and Especially Unsafe During the Hurricane Season. LIEUT. DYER'S OBSERVATIONS. A NAVIGATOR'S REPORT. THE PRESENT SEASON.

    Los Angeles Times (1886-1922). Los Angeles, Calif.: Apr 1, 1889. pg. 4, 1 pgs

    Abstract (Summary) Capt. Selfridge, U.S.N., was found at the Navy Department yesterday, poring over a chart of the harbor of Apia, which he visited several years ago. He said that while it was a very bad harbor, it was the best on the island of Upola.

    Original Newspaper Image (PDF)

  2. Cyclone Devastates Australian City of Darwin; at Least 50 Die; CYCLONE

    Los Angeles Times (1923-Current File). Los Angeles, Calif.: Dec 26, 1974. pg. A1, 2 pgs

    Abstract (Summary) Cyclone Tracy's 125-m.p.h. winds devastated the northern Australia port city of Darwin Wednesday, killing at least 50 persons and leaving half of the city's 40,000 inhabitants homeless. Gusts to 175 m.p.h. were reported.

    Original Newspaper Image (PDF)

  3. Flood Survivors Find Only Ruin In Mozambique; Flood Survivors Are Stranded in Ruin in Mozambique

    RACHEL L. SWARNS, New York Times (1923-Current file). New York, N.Y.: Mar 4, 2000. pg. A1, 2 pgs

    Abstract (Summary) THIRD OF FEBRUARY, Mozambique, March 3—The old people called to each other from the treetops, and their cries soon filled the night.

    Original Newspaper Image (PDF)

Taken from ProQuest's Historical Newspapers.

Dissertations

  1. ON THE PHYSICAL PROCESSES RESPONSIBLE FOR TROPICAL CYCLONE MOTION

    by CHAN, JOHNNY CHUNG LEUNG, Ph.D., Colorado State University, 1982, 211 pages; AAT 8306554

    Abstract (Summary)
    This paper investigates the possible physical processes involved in tropical cyclone motion. The first part analyzes the relation between the synoptic-scale flow around tropical cyclones and cyclone movement. It was found that, in most cases, tropical cyclones in the Northern (Southern) Hemisphere move to the left (right) of and faster than their environmental flow.

    To understand these observations, an analytical study using a simplified form of the vorticity equation was performed. The results show the importance of the environmental flow and change in the Coriolis parameter across the cyclone in determining cyclone motion. The locations of maximum local changes of relative vorticity can be interpreted to correspond to the observational results.

    The interaction between the vortex and the environmental flows was further investigated by analyzing the radial equation of motion. Results from a simple model and observations both indicate the presence of radial accelerations which can be explained in terms of parcel trajectories. The differences of radial accelerations between the right and left sides of the cyclone (with respect to cyclone direction) was found to be proportional to the speed of the cyclone. Differences in radial accelerations between the front and the back of a cyclone appear to be related to a change in cyclone direction.

    Vorticity budgets for cyclones with different speeds and turning directions were then analyzed. The horizontal advection and the divergence terms were found to dominate over the tilting and vertical advection terms. These results are consistent with those from the analytical study of the vorticity equation described above.

    Combining the theoretical and observational results, a hypothesis is proposed to describe the possible physical processes involved in tropical cyclone motion. Interaction of the vortex and environmental flows brings about a vorticity increase to the front of the cyclone. This increase in relative vorticity forces a mass adjustment through subsidence, producing a net tropospheric warming and eventually a new center of vortex circulation. The movement of a tropical cyclone is therefore one of "propagation", with eye wall clouds continually reforming around the new "eye" and dissipating around the old center.

    For full-text documents see ProQuest's Dissertations & Theses Database

  2. Role of equatorial waves in tropical cyclogenesis

    by Schreck, Carl J., III, Ph.D., State University of New York at Albany, 2010 , 161 pages; AAT 3418475

    Abstract (Summary)
    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.

    More storms are attributed to TD-type disturbances than to any other wave type in all of the Northern Hemisphere basins. In the Southern Hemisphere, however, ER waves and TD-type disturbances are equally important as precursors. Fewer storms are attributed to MRG waves, Kelvin waves, and the MJO in every basin. Although relatively few storms are attributed to the MJO, tropical cyclogenesis is 2.6 times more likely in its convective phase compared with its suppressed phase. This modulation arises in part because each equatorial wave type is amplified within MJO's convective phase. The amplification significantly increases the probability that these waves will act as tropical cyclone precursors.

    A case study from June 2002 illustrates the effects of a series of Kelvin waves on two tropical cyclone formations. These waves were embedded in the convective phase of the MJO. Together, the MJO and the Kelvin waves preconditioned the low-level environment for cyclogenesis. The first Kelvin wave weakened the trade easterlies, while the subsequent waves created monsoon westerlies near the equator. These westerlies provided the background cyclonic vorticity within which both storms developed.

    The effects of tropical cyclone-related rainfall anomalies are also investigated. In the wavenumber-frequency spectrum for rainfall, tropical cyclones can inflate the power for shorter wavelength westward propagating waves by up to 27%. This spectrum contains signals from all longitudes, but the greatest contamination occurs in regions like the Philippines where tropical cyclones are most frequent. Here, tropical cyclones contribute more than 40% of the rainfall variance in each filter band. To mitigate these effects, tropical cyclone-related anomalies were removed before filtering in this study.

    For full-text documents see ProQuest's Dissertations & Theses Database

  3. Tropical cyclone rainfall: An observational and numerical study of the structure and governing physical processes

    by Lonfat, Manuel, Ph.D., University of Miami, 2004 , 135 pages; AAT 3159143

    Abstract (Summary)
    Fresh water flooding has become the largest threat to life at hurricane landfall in the United States, in part because of a lack of skill of current Quantitative Precipitation Forcast (QPF) methods. This study aims to develop a global climatology of tropical cyclone (TC) rainfall and to improve our understanding of physical processes that affect the TC rainfall structure and distribution, using satellite observations and numerical simulations. First, the TC rainfall distributions with respect to the storm intensity and location are examined, using global satellite observations from the Tropical Rainfall Measuring Mission (TRMM). Secondly, numerical simulations using the Penn State/National Centers for Atmospheric Research (NCAR) mesoscale modelling system, version 5 (MM5), are performed to study how specific processes affect the cyclone rainfall. The presence of moisture and momentum sources on a storm's inner core is investigated using a method that modifies the environmental conditions in the model.

    The mean TC rainfall distribution and the first order asymmetry vary with storm intensity and geographical location among the six oceanic basins. The mean rainfall increases with storm intensity within 250 km of the storm center while the radius of maximum rainfall decreases. The asymmetric component is determined by the first-order Fourier decomposition in a coordinate system relative to storm motion and shear. The rainfall asymmetry with TC motion varies significantly with both storm intensity and geographic location. For the global average of all TCs, the maximum rainfall is located in the front quadrants. However, the global composite asymmetry is larger when analysed with respect to shear. The asymmetry is observed down-shear left (right) in the Northern (Southern) Hemisphere for shear values >7.5 m s -1 . The analysis is further extended to examine the net effect of the storm motion and the vertical wind shear. It is found that the storm-motion induced rainfall asymmetry is comparable to that induced by the shear when the shear is <5 m s -1 . TC propagation speed becomes more important in the relatively low shear environment. The overall rainfall asymmetry, in all oceanic basins, depends on the angle and relative magnitude between the storm motion and shear vectors.

    The combined effect of shear and TC propagation speed is further investigated using numerical simulations of Hurricane Floyd (1999). Floyd was a well-observed intense storm that experienced variable environmental shear, from relatively low shear to close to 15 m s -1 high shear during its life cycle. (Abstract shortened by UMI.)

    For full-text documents see ProQuest's Dissertations & Theses Database