A superficial assessment indicates that some effects fit the classical model (as given by previous events), but many did not. Another area where highly anomalous conditions were experienced was Kenya and the horn of Africa region where heavy rains were surely linked to very high SSTs in equatorial Indian Ocean (above 95th percentile, above 29℃) after about September 1997. The rains in northeastern Kenya and southern Somalia were apparently the heaviest since 1961. They began in October 1997 and continued through January 1998. Insect and disease outbreaks followed in the flood waters and, in particular, the population of mosquitoes increased, leading to proliferation of vector-borne diseases such as malaria, dengue fever and Rift Valley fever ― not only in livestock but also with tens of thousands of cases in humans (P. Epstein, personal communication). In several parts of the world, cholera developed as a consequence of unsafe water supplies and poor hygiene. Major convection in this area clearly had an impact on the divergent atmospheric circulation and there is good reason to believe it altered teleconnections. It is likely that these changes had impacts on Australia, India, Southern Asia, - all regions where conditions were not as dry as expected from past events - and elsewhere.
Forecasts of the northern winter were made well ahead of time and were widely publicized and, fortunately, were generally excellent. In the United States, patterns of temperature and precipitation anomalies were forecast based in part on model output but in large part on statistical relationships developed in the Climate Prediction Center of NOAA, and matched the observed remarkably well.
4. RESEARCH QUESTIONS
Many research questions arise from this event and they are detailed in Trenberth (1998). In brief, they include the following. The role of MJOs in the 1997/98 ENSO is a key question that can and should be explored with diagnostic and numerical experimentation studies to determine the extent to which these were essential parts of the development or merely "embroidery". We also need to answer how well the event was forecast throughout, both for SST forecasts and the weather regimes around the world (coastal erosion, precipitation, temperature, storminess, flooding, drought, fires, etc). In addition, an important research question is why some models did well and other models did not do well, in spite of strong similarities in several of the models. Unraveling the role of initial conditions for each model, the ocean physics, the atmospheric physics, and the coupling is a challenging task.
