Recent Accomplishments of the US CLIVAR MJO Working Group (MJOWG)
Duane Waliser and Ken
Sperber
(Reprinted from UCLA
Tropical Meteorology and Climate Newsletter, No. 82, 1 October 2008)
In spring 2006, US CLIVAR established the Madden-Julian Oscillation (MJO)
Working Group (MJOWG;
http://www.usclivar.org/mjo.php). The formation of
this roughly 2-year limited lifetime WG was motivated by: 1) the wide
range of weather and climate phenomena that the MJO interacts with and
influences, 2) the fact that the MJO represents an important, and as yet
unexploited, source of predictability at the subseasonal time scale, 3)
the considerable shortcomings in our global climate and forecast models
in representing the MJO, and 4) the need for coordinating the multiple
threads of programmatic and investigator level research on the MJO.
MJOWG tasks have involved the development of diagnostics for assessing
model performance in both climate simulation and extended-range/subseasonal
forecast settings as well as the development of a consistent and
coordinated approach to subseasonal, specifically MJO, forecasting. The
purpose of this newsletter item is to make the readers aware of these
activities. The items below highlight the main activities of this
working group.
MJO Simulation Diagnostics
The Madden-Julian Oscillation (MJO) interacts with, and influences, a
wide range of weather and climate phenomena (e.g., monsoons, ENSO,
tropical storms, mid-latitude weather), and represents an important, and
as yet unexploited, source of predictability at the subseasonal time
scale. Despite the important role of the MJO in our climate and weather
systems, current global circulation models (GCMs) exhibit considerable
shortcomings in representing it. These shortcomings have been documented
in a number of multi-model comparison studies over the last decade.
However, diagnosis of model performance has been challenging, and model
progress has been difficult to track, due to the lack of a coherent and
standardized set of MJO diagnostics. A chief objective of the US CLIVAR
MJO Working Group is the development of diagnostics for objectively
evaluating global model simulations of the MJO. Motivation for this
activity is reviewed, and the intent and justification for a set of
diagnostics is provided, along with specification for their calculation,
and illustrations of their application. The diagnostics range from
relatively simple analyses of variance and correlation diagnostics, to
more sophisticated space-time spectral analyses and computation of
empirical orthogonal functions. These diagnostic techniques are used to
construct composite life-cycles, to identify associations of MJO
activity with the mean state, and to describe interannual variability of
the MJO. A link to the diagnostics are posted on the MJOWG web site (or
see direct link at:
http://climate.snu.ac.kr/mjo_diagnostics/index.htm)
and a journal article has been submitted that describes this effort. See
US CLIVAR Madden-Julian Oscillation Working Group, 2008: MJO Simulation
Diagnostics, J. Clim., Submitted.
Application of MJO Simulation Diagnostics to Climate Models
The ability of 8 climate models to simulate the Madden-Julian
Oscillation (MJO) has been examined using recently developed diagnostics
for MJO simulation. This study focuses on the boreal wintertime
(November-April). The mean state, variance map and equatorial space-time
spectra of 850hPa zonal wind and precipitation are compared with
observations. Although many of participating model have stronger
sub-seasonal variability of precipitation, only one model produces
dominant spectral peak in the MJO space-time scale as in observation. It
is revealed that the MJO signal from large-scale circulation (850hPa
zonal wind) is better than that of latent heating (rainfall) in most of
the models. Multivariate empirical orthogonal function (EOF) method is
suggested as useful tool to extract model's own MJO-like phenomenon and
it is compared with single variable EOF analysis. By compositing on the
phase and amplitude of the two leading principal components, the decay
time scale of canonical strong MJO events is assessed for different
initial phases of the in the MJO life-cycle. The MJO decay (e-folding)
time scale depends on initial phase and all models have shorter period
(~23-29days) compared to observation (~31days). The important features -
surface latent heat flux, boundary layer (925hPa) moisture convergence
and vertical structure of moisture - associated with the model's MJO are
investigated. Frictional moisture convergence ahead (east) of convection
seems to be a mechanism of eastward propagation in most of the models,
supporting to current paradigm. Some models are able to reproduce the
observed geographical difference in vertical structure of moisture
associated with the MJO. Also examined in this effort are the
characteristics of the models' precipitation dependence on lower
tropospheric relative humidity and fraction of stratiform rainfall, and
the implications on the fidelity of the MJO simulation. A journal
article is being prepared that describes this effort (contact: kim@climate.snu.ac.kr;
Kim et al., 2008: Application of MJO Simulation Diagnostics to Climate
Models, J. Clim., In Preparation)
MJO Workshop: New Approaches to Understanding, Simulating, and
Forecasting the Madden-Julian Oscillation
Through the sponsorship of US CLIVAR and International CLIVAR, the MJOWG
hosted an invitation-only workshop that gathered researchers and
forecasters of the Madden-Julian Oscillation to discuss new approaches
to understanding, simulating, and forecasting the MJO in the context of
weather-climate connections. The workshop was held November 5-7, 2007,
in Irvine, CA. The workshop was attended by members of both the MJO
research and forecasting communities. Its objectives included: (1)
Introducing new diagnostics designed to systematically evaluate model
simulations and forecasts of the MJO; (2) Identifying key limits to our
understanding of the MJO as well as to the processes that might be
crucial for modeling the MJO; and (3) Developing integrative approaches
to tackle the problems associated with understanding, simulating, and
forecasting the MJO. The workshop was organized into six half-day
sessions over three days. The first day emphasized diagnostics and
models, and forecast metrics. The second day focused on vertical and
multi-scale structures, as well as theory and modeling. The theme of the
third day was integrative modeling approaches with sessions on existing
and planned efforts, and new initiatives and next steps. Each session
included three invited talks, a poster session, and a one-hour
discussion. Most of the oral and poster presentations can be found at:
http://www.joss.ucar.edu/joss_psg/meetings/Meetings_2007/MJO/index.html,
and a meeting summary is in press with the Bulletin of the
Meteorological Society (BAMS), with an Early Online Release version
available at:
http://ams.allenpress.com/archive/1520-0477/preprint/2008/pdf/10.1175_2008BAMS2700.1.pdf.
Operational Forecasting of the MJO
The development and operational implementation of an MJO forecast metric
is a key goal of the MJOWG. We have developed a version of the Wheeler &
Hendon combined EOF that is being applied operationally, in a
coordinated manner, to a number of forecast centers' extended-range
forecasts and their ensembles. Participation in this activity, through
its development phase, has been from ECMWF, UKMO, CMA, BMRC, and NCEP.
We recently received endorsement for this activity from the Working
Group on Numerical Experimentation (WGNE), and through collaboration
with WGNE, are formally establishing this methodology and inviting wider
participation from other international forecast centers. Based on this
invitation, JMA and CPTEC have also become participants. At this time,
the centers are sending their MJO forecast metric data to CPC/NOAA for
uniform, real-time web presentation and potential use and development of
a multi-model ensemble prediction of the MJO (contact Jon.Gottschalck@noaa.gov
for details). More information on this effort can be found in an article
in the next CLIVAR Exchanges (October 2008;
http://www.clivar.org/publications/exchanges/exchanges.php),
and a journal article is being prepared for BAMS.
To more formally assess the MJO skill of the operational forecasting
effort, we are considering the development of hindcast experiments.
These experiments would provide valuable information with respect to MJO
predictability from different phases of the MJO life-cycle, as well as
the MJO's associated impacts on other weather/climate phenomena.
Additionally, it is possible that select MJO hindcast periods could be
adopted as benchmark tests for model development by the numerical
weather prediction community. Also under consideration is the
development of a forecast metric that is more specific to the boreal
summer Asian monsoon domain, so as to better capture the northward
propagating intraseasonal convective signal that affects India and
southeast Asia.
Contact:
Duane Waliser
Ken Sperber
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