Tropical/Extratropical Interaction Mechanisms at the Intraseasonal Time Scale

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This project has the potential to lead to an improvement of the subseasonal (2-6 week) probabilistic weather forecasts of temperature and precipitation for North America. Support for this outcome is based upon the previous research by the team on the influence of tropical weather on mid-latitude weather, which has contributed to the development of the probabilistic subseasonal weather forecast method used by NOAA. This project will also train a graduate student to become an independent scientist. Besides participating in the usual activities of publishing papers and giving conference presentations, the team will work with personnel at Penn State's Center for Science and the Schools to conduct a five-day workshop on subseasonal to seasonal (S2S) prediction for middle and high school teachers from low socioeconomic and racially diverse urban and rural Pennsylvania school districts that serve populations highly underrepresented in science, technology, engineering, and math fields. The teachers will attend lectures on the techniques used for S2S forecasting, and participate in relevant inquiry-based activities. The team will provide follow-up support as the teachers implement the workshop activities in their classrooms.In the tropics, the dominant pattern on the intraseasonal time scale, the Madden-Julian Oscillation (MJO), is characterized by organized precipitation systems that propagate eastward encircling the tropics on a timescale of 30-70 days. The importance of the MJO for forecasting is evidenced by the use of the state of the MJO in week-3 and week-4 probabilistic forecasts by the NOAA/Climate Prediction Center. Although much progress has been made during the past three decades toward understanding how tropical convective heating influences the weather in mid-latitudes, there are still important unaddressed questions. This project will focus on questions that have not yet been investigated or have received little previous attention: (1)investigation of how Rossby waves are excited by MJO-related convection in the tropics propagate pole-ward,and impact weather in the mid-latitudes; (2) variation in the horizontal and vertical structure of the latent heat released in convections within the MJO event, and its impact in a key region, the central subtropical North Pacific; and (3) role of inertio-gravity waves excited by MJO-related convections in connecting tropical convections to weather over large distances across the Earth, e.g., teleconnection patterns. The team will also address the following questions: Why does the high latitude component within teleconnection patterns persist for a much longer time period than do their lower latitude counterparts? What is the impact of inertio-gravity waves excited by the MJO on mid-latitude weather? The topic is particularly important because active teleconnection patterns have a large influence on the weather up to 6 weeks later. The approach includes the use of observational datasets and computer model calculations. The computer model will be used to isolate and to better understand the key physical processes that are responsible for the tropical-extratropical teleconnections.This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.