HR: 0830h
AN: A41B-02    [Abstracts]
TI: A Hidden Markov Model of Sub-seasonal Australian Monsoon Variability Over Queensland
AU: * Robertson, A W
EM: awr@iri.columbia.edu
AF: International Research Institute for Climate Prediction, The Earth Institute of Columbia University, 61 Route 9W, Palisades, NY 10960 United States
AU: Kirshner, S
EM: skishne@ics.uci.edu
AF: School of Information and Computer Science, University of California, Irvine, Irvine, CA 92697 United States
AU: Smyth, P
EM: smyth@ics.uci.edu
AF: School of Information and Computer Science, University of California, Irvine, Irvine, CA 92697 United States
AU: Charles, S P
EM: Steve.Charles@csiro.au
AF: CSIRO Land and Water, Floreat Park, Wembley, WA 6913 Australia
AU: Bates, B C
EM: Bryson.Bates@csiro.au
AF: CSIRO Land and Water, Floreat Park, Wembley, WA 6913 Australia
AB: Daily rainfall occurrence and amount at 11 stations over North Queensland are examined during summer 1958--1997, using a Hidden Markov Model (HMM). Daily rainfall variability is described in terms of the occurrence of five discrete "weather states," identified by the HMM. Three states are characterized respectively by very wet, moderately wet, and dry conditions at most stations; two states have enhanced rainfall along the coast and dry conditions inland. Each HMM rainfall state is associated with a distinct atmospheric circulation regime. The two wet states are accompanied by monsoonal circulation patterns, with large-scale ascent, low-level inflow from the northwest, and a phase reversal with height. An upper-level monsoon trough to the east depresses the tropopause, especially for the very-wet state. The dry state is characterized by the opposite circulation anomalies. The coastal rainfall states are characterized by low-level southeasterlies from the ocean, and NW--SE midlatitude troughs. Variability of the monsoon on daily time scales and longer is interpreted in terms of the estimated daily sequence five HMM rainfall states. Large sub-seasonal variability is identified in terms of active and break phases, and a highly variable monsoon onset date. The occurrence of the very-wet and dry states is found to be somewhat modulated by the Madden-Julian oscillation. Stochastic simulations of daily rainfall occurrence and amount at the 11 stations are generated by introducing predictors based on large-scale precipitation fields from reanalysis data, and an atmospheric general circulation model.
DE: 1833 Hydroclimatology
DE: 3319 General circulation
DE: 3337 Numerical modeling and data assimilation
DE: 3354 Precipitation (1854)
DE: 3364 Synoptic-scale meteorology
SC: Atmospheric Sciences [A]
MN: 2005 Joint Assembly