JP3.10
Relationships between the Madden-Julian Oscillation and Atlantic-East Pacific tropical cyclone activity
Bradford S. Barrett, Univ. of Oklahoma, Norman, OK; and L. M. Leslie
The Madden-Julian Oscillation (MJO), a forty- to sixty-day global wavenumber one oscillation, affects many components of the earth-atmosphere system. Both low-level 850 hPa and upper-level 200 hPa winds were observed to oscillate within the frequency identified by Madden and Julian (1971), although their extent varies with basin. The lower tropospheric disturbance was found confined to the Pacific region, while the upper tropospheric disturbance was found to circumnavigate the earth.
Forecasting tropical cyclogenesis has proven problematic, even as other facets of TC forecasting, especially track forecasting, have experienced significant gains in the last ten years. While the classical genesis parameters (Gray 1968), including sea surface temperatures above 26.5 C, a deep thermocline, sufficient Coriolis contribution, low vertical shear of the horizontal wind, a cyclonic low-level vorticity anomaly, high low- and middle-tropospheric relative humidity, and a persistent region of organized convection, are necessary for genesis, they are not sufficient. Individual TCs form infrequently and sporadically within large areas of otherwise favorable environmental conditions. In this paper, we present results that demonstrate the MJO's significant modulation of TC activity, segregated both by basin and sub-basin. We provide an important, and heretofore missing, link between TC activity and otherwise favorable environmental conditions.
Recent research has examined the connection between the MJO and tropical cyclone (TC) activity. However, because the MJO physical expression varies by region, relationships must be developed separately for each basin and sub-basin. We focus on the East Pacific, North Atlantic and sub-basins over a thirty-year period, expanding the findings of earlier studies which examined either an entire basin, or a sub-region, but not both, and which were completed before the most recent very active North Atlantic period. By comparing TC activity recorded in the “best track” database with an operational ten-index, three-phase MJO composite generated by the NOAA CPC, we found that the MJO strongly modulates the climatological pattern of cyclogenesis in each basin and sub-basin. Not surprisingly, the relationships form a classical teleconnection, e.g, an enhanced-phase MJO over the Indian basin impacts TC activity in the opposite hemisphere. Strong statistical relationships, significant at the 95% confidence level, were also observed for TC intensity and landfall. We believe that these results represent a significant breakthrough in the forecasting of TC activity, from genesis to intensification to landfall, in the five- to twenty-day lead time, and that they support the observation that tropical cyclogenesis tends to cluster in space and time. These results, along with the relationships between atmospheric oscillations on longer timescales and TC activity in the East Pacific, North Atlantic, and sub-basins, will be presented in this paper.
Joint Poster Session 3, Tropical Cyclones and Climate Change Poster Session
Monday, 21 January 2008, 2:30 PM-4:00 PM, Exhibit Hall B
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