Modeling, Simulating, and Forecasting Subseasonal Atmospheric Variability III: Posters
Presiding: D Waliser, California Institute of Technology; K Weickmann, National Oceanic and Atmospheric Administration
A41B-01 0830h
MJO Modulation of Ocean Chlorophyll: Can the fishing industry benefit from subseasonal forecasts?
Previous studies have noted considerable influences by the Madden-Julian Oscillation on a number of weather and climate processes. These include a considerable influence over low-frequency weather variations over much of the Tropics, the onsets and breaks of the Asian-Australian monsoon systems, extra-tropical synoptic variability, tropical storm and hurricane development in the Pacific and Atlantic sectors, and possibly the timing and strength of El Nino / La Nina events. The material in this presentation will show that the MJO also produces a significant basin-wide influence on the tropical Indo-Pacific chlorophyll distribution. Diagnostic analysis will also be shown that indicates that vertical mixing associated with wind variations are in part responsible for these variations. These results, in conjunction with recent studies indicating the MJO may have useful predictability with lead times up to 2-3 weeks, indicate that operational predictions of the MJO may also be of use to the commercial fishing industry.
A41B-02 0830h
A Hidden Markov Model of Sub-seasonal Australian Monsoon Variability Over Queensland
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.
A41B-03 0830h
MJO-Related Oceanic Kelvin Waves and ENSO Cycle: A Study With NCEP Global Ocean Data Assimilation System
The surface wind anomalies associated with the Madden-Julian oscillation(MJO) appear to play a critical role during the onset and termination phases of ENSO. The characteristics of the MJO-related oceanic Kelvin waves have not been systematically studied due to a lack of ocean reanalysis that resolves intraseasonal variability. This study uses the operational ocean reanalysis for 1982-2003 produced by the state-of-art global ocean data assimilation system at NCEP to explore the relationship between SST anomalies of ENSO and MJO-related oceanic Kelvin waves. The first four extended empirical orthogonal functions of the depth of 20° C isotherm are used to represent the dominant oceanic Kelvin waves. The wave activity is measured by seasonal variance of oceanic Kelvin waves (SVKW) at 130° W. SVKW peaks are associated with the onset stage of warm ENSO events since they occur during the transition period and tend to produce positive tendency in NINO3.4 and heat content, and lead mature phases by 5-11 months. MJO-related oceanic Kelvin wave activity is also shown to impact the growth and termination of warm events. The consistent relationships do not occur in cold events. A real time monitoring tool using SVKW index is proposed to support the official ENSO forecast at NCEP.
A41B-04 0830h
ENSO, Subseasonal Variability and Extreme Winter Weather Events over the United States
The ENSO/weather connection clearly depends on a number of different process that include the large-scale seasonal mean response of atmospheric to tropical Pacific SST anomalies, and potential attendant changes in various subseasonal low frequency variations such as the PNA and blocking. These linkages are complicated by potential nonlinearities that result in the interactions between the various time and space scales. In this study, we force the NSIPP-1 AGCM with observed SST to examine the link between ENSO and extreme precipitation events over the United States. In addition to the link to EL Nino, We also quantify the impact of other subseasonal modes of variability including the PNA and AO on extreme weather throughout the continent. Results from the simulations are compared with observations that are composited according to these atmospheric indices as well as ENSO.
A41B-05 0830h
The WRF Model Application In NMC/CMA
The Weather Research and Forecast (WRF) model is a new model development effort undertaken jointly by the NCAR, NOAA, and a number of collaborating institutions and university scientists. The WRF model version 1.3, which still is at research stage in NMC/CMA, was installed on IBM SP2 machine in 2002. It ingests the global model T213 fields as initial field and boundary conditions every 6 hours. The comparison the different horizontal resolution between 20km and 5km shows that the model running with high horizontal resolution can catch much more mesoscale features. But the verification results show that performance of the 24 hours precipitation forecast is not good. Recently, the WRF-3DVAR was used, which was expected to promote the model performance. However, the system is not better than other operational system in NMC/CMA.
A41B-06 0830h
Simulation of Northern Hemisphere Extratropical Modes of Variability in Subseasonal Forecasts of the NCEP Climate Forecast System
The North Atlantic Oscillation (NAO) and the Pacific North American (PNA) teleconnection patterns constitute important modes of variability in the Northern Hemisphere extratropical atmosphere. Together they explain progressively more amount of variability as the averaging period is increased. They therefore become relatively more important in the sub seasonal time range (from 1-2 weeks up to a season) compared to daily forecasting. We will compare and contrast the observed three-dimensional structure of these modes with those obtained in a GCM. Here we investigate the impact of increasing horizontal resolution on the prediction of these climate modes in a fully coupled ocean-land-atmosphere model, which has a high vertical resolution atmospheric component. A series of retrospective forecasts, each integrated over a period of 60+ days during the 1997 to 2004 timeframe with the new NCEP Climate Forecast System are studied for the skill in predicting these patterns. The first two weeks of these integrations can be used to study prediction skill and predictability. The two and three-dimensional structure of the PNA and NAO will also be tracked beyond 2 weeks.
A41B-07 0830h
A High Resolution Coupled General Circulation Model for Subseasonal Forecast: Impact of Horizontal Resolution on Simulation and Retrospective Forecast of Intraseasonal Oscillations
General circulation models are notorious for their misrepresentation of Tropical Intraseasonal Oscillations. Hitherto, some improvements due to (i) increased vertical resolution, (ii) the type of convective parameterizations and (iii) coupling to ocean have been reported. Here we investigate the impact of increasing horizontal resolution in a high vertical resolution atmospheric component of a coupled ocean - atmosphere model. The high vertical resolution assures consistency with the horizontal discretization in both coarse and dense configurations. A series of retrospective forecast of Tropical Intraseasonal Oscillations from 1997 to 2004 performed with the GFS-T126L64/MOM3 is compared to the results of the operational version of the NCEP coupled seasonal forecasting dynamical system CFS i.e., GFS-T62L64/MOM3. In order to account for the effects of model drift and initialization shocks to the TIO, we further extend this comparison to long coupled experiments where the initial adjustment period is removed.
A41B-08 0830h
Ozone and Nitric Acid Variability in the Upper Troposphere and Lower Stratosphere Measured during the Polar Aura Validation Experiment
Understanding the response of stratospheric and tropospheric constituents to climate and chemical change requires synthesizing a complex combination of physical and chemical processes that operate simultaneously on a wide range of spatial and temporal scales to produce the large-scale global distributions observed by satellites. However, retrieval algorithms are difficult to develop in the critical upper tropospheric, tropopause and lower stratospheric regions, where the radiative properties of trace gases most affect the global climate. This is because most retrieval algorithms depend on an initial a priori profile assumption based on a geographical measurement climatology, but the actual vertical mixing ratio gradients are large across the tropopause, which varies in height based on the location of geophysical features. In this presentation we show high-resolution, accurate in situ correlative ozone and nitric acid measurements from the NASA DC-8 during the Polar Aura Validation Experiment (PAVE) in January-February of 2005. In addition to providing calibrated correlative measurements, these high-resolution measurements help to characterize the variability of ozone and nitric acid in the near-tropopause region. We use our measurements to illustrate both vertical and horizontal variability under various synoptic conditions encountered during the mission. During late winter ozone acts as a conserved dynamical tracer in the lower stratosphere, and we examine correlations of ozone with measured nitric acid and modeled potential vorticity, as well as calculate the observed ozone variance power spectrum and structure functions to better quantify mixing and eddy dissipation rates at scales that are too fine for the satellite instruments and ozone lidars to resolve, but that span the subrange between the inertial (isotropic) and buoyant (anisotropic) turbulent mixing scales. Accurate characterization of mixing of chemical species and energy dissipation in this subrange (200m - 20km) is critical to the accurate quantification of irreversible material exchange across the tropopause. We also hope to identify dynamical structures where atmospheric inhomogeneity may present a particular challenge to satellite retrieval algorithms.
A41B-09 0830h
A Multiseason Comparison of the Forecast Skills among Three Numerical Models over Southcentral United States
During the summer 2003 and winter 2003-2004, three mesoscale numerical models, the fifth-generation Pennsylvania State University-NCAR Mesoscale Model (MM5), Navy's Coupled Ocean/Atmospheric Mesoscale Prediction System (COAMPS) and the Weather Research and Forecasting model (WRF), were operationally run at a horizontal resolution of 27 km twice daily in Jackson State University (JSU). Three models were run by the initial and lateral boundary conditions from AVN data. The purpose of this paper is to evaluate the performances of three models during these two seasons. It was found that the temporal variation of distribution and strength of mean error (ME) biases at 12, 24 and 36h was rather weak for surface temperature, sea level pressure and surface wind speed. During two seasons, the MM5 underpredicted the seasonal precipitation while the COAMPS and WRF overpredicted. This is consistent with the statistical score analyses of rainfall. The Bias scores revealed that the MM5 yielded an underprediction of precipitation, especially for heavier rainfall events. Due to the under estimate of rainfall areas and strength, the MM5 presented the lower TS, POD and KSS scores at lighter rainfall events compared to the COAMPS and WRF. At moderate to heavier thresholds, three models produced rather low KSS and POD scores that are consistent with the high FAR values. The WRF skills in predicting precipitation heavily depend on the performance of cumulus parameterization scheme. Instead of Kain-Fritsch scheme, using other two schemes, Grell-Devenyi and Bette-Miller-Janjic, in the WRF for warm season 2003 demonstrated that the precipitation overprediction had been efficiently suppressed. Overall, the performances of three models revealed that the best skill is at 12h and the worst at 36h.