Assessment of Intraseasonal to Interannual Climate Prediction and Predictability (2010) / Chapter Skim
Currently Skimming:
4 Case Studies
4 Case Studies
Pages 101-123
The Chapter Skim interface presents what we've algorithmically identified as the most significant single chunk of text within every page in the chapter.
Select key terms on the right to highlight them within pages of the chapter.
From page 101... ...
During the cold phase, the eastern tropical Pacific SSTA is negative, the trade winds are anomalously strong, and the precipitation is tightly confined to the warm pool region of the western Pacific. Typically, the time between warm events is around 2 to 7 years; however, there is also considerable modulation of the ENSO cycle on decadal timescales.
|
From page 102... ...
works as follows. If a positive eastern equatorial SSTA exists, the temperature gradient between the eastern Pacific and the western Pacific is reduced, which then produces a weakening of the easterly trade winds, augmenting the warming in the eastern Pacific.
|
From page 103... ...
was completed in 1994 to include 70 moorings. The moorings provide winds, sea surface temperature, relative humidity, air temperature, and subsurface temperature at 10 depths in the upper 500 m.
|
From page 104... ...
. During the mid to late 1990s dynamical models began to make much better use of observational estimates of the state of the sub-surface ocean in the tropical Pacific, which led to notable improvements in forecast quality.
|
From page 105... ...
two U.S. national models improves this particular skill metric and suggests that the United States is indeed well positioned to make multi-model operational ENSO predictions.
|
From page 106... ...
. These hindcast datasets provide a test-bed for assessing forecast quality and forecast uncertainty based upon uncertainty in model formulation.
|
From page 107... ...
. Chronic biases in the coupled models in their mean states and intrinsic ENSO modes remain, and it is believed that these biases have a deleterious effect on SSTA forecast quality and the associated teleconnections.
|
From page 108... ...
. Examination of the boreal summer rainfall maps shows that positive rainfall anomalies in the western and central Indian Ocean occur in conjunction with negative rainfall anomalies over a region extending between India and the western equatorial Pacific.
|
From page 109... ...
; right panels are for the boreal summer (May–October)
|
From page 110... ...
For the boreal summer case, Kemball-Cook and Wang (2001) show that there is a systematic intraseasonal change in the spatial structure and propagation characteristics of the MJO.
|
From page 111... ...
The colors indicate OLR anomalies, with red corresponding to suppressed convection and blue corresponding to enhanced convection. Essentially, large differences can exist among MJO events in different years.
|
From page 112... ...
. Forecast Performance Based on the results from empirical and dynamical modeling studies discussed above, there has been ample reason to push towards an operational MJO prediction capability.
|
From page 113... ...
While dynamical models have not simulated the MJO in a particularly faithful manner, there have been improvements in their performance. An excellent example of improvement in forecast model quality is given in Figure 4.7, which shows the evolution of the ECMWF hindcast skill for the MJO during the Tropical Ocean Global Atmosphere Coupled Ocean Atmosphere Response Experiment (TOGA COARE)
|
From page 114... ...
. The motivation for having such a metric is that it allows for a more quantitative assessment of forecast quality, the ability to track model forecast quality over time, the capability to measure potential model improvements relative to the MJO, and the means to develop a multi-model ensemble forecast of the MJO.
|
From page 115... ...
. While the above efforts will facilitate continued development and improvements in operational MJO predictions, it is certain that capturing the forecast quality associated with the MJO is most strongly hampered by the systematic biases in the models, such as those illustrated in Figure 4.8.
|
From page 116... ...
. SOIL MOISTURE The use of realistic soil moisture initialization can potentially improve precipitation and air temperature forecasts on ISI time scales.
|
From page 117... ...
In segment B, a positive evaporation anomaly can lead to a positive precipitation anomaly, though in certain situations, it can instead lead to a negative precipitation anomaly. In segment C, a positive precipitation anomaly leads to a positive soil moisture anomaly.
|
From page 118... ...
AGCMs differ significantly in their estimates of how soil moisture variations affect precipitation and air temperature, and (2) they do nevertheless tend to agree that certain regions during certain times of year are more prone to soil moisture impacts on the atmosphere than others.
|
From page 119... ...
precipitation predictions (though significant impact on air temperature predictions) associated with soil moisture initialization (e.g., Schlosser and Milly, 2002)
|
From page 120... ...
Forecast Performance The obvious extensions to the idealized, model-based studies discussed in "Scientific Basis for Prediction" section are studies that use true forecast systems and observations of forecasted variables to examine the degree to which realistic soil moisture initialization improves forecast quality. Fennessy and Shukla (1999)
|
From page 121... ...
FIGURE 4.11. Conditional improvement in forecast accuracy for air temperature related to improved land initialization.
|
From page 122... ...
Additional work is needed to ensure that the simulated processes interact with each other in realistic ways. Of course, even if all model formulations, and thus the simulated coupling strength, were perfect, prediction quality would still be limited by deficiencies in our ability to assign realistic global distributions of soil moisture initial conditions.
|
From page 123... ...
Case Studies 123 of the meltwater may flow into streams. This potential use of wintertime soil moisture to add skill to springtime water resources prediction is not yet fully tapped.
|
Key Terms
This material may be derived from roughly machine-read images, and so is provided only to facilitate research.
More
information on Chapter Skim is available.