Technology on the Cutting Edge of Weather Research and Forecasting Dr. Dave Dempsey Professor of Meteorology Department of Geosciences, SFSU

Technology on the Cutting Edge of Weather Research and Forecasting How modern weather forecasting works How to make better weather forecasts

Pre-modern Weather Forecasting A Rule of Thumb: Red sky at morning, sailors take warning; red sky at night, sailors’ delight

How Modern Weather Forecasting Works The atmosphere is mostly a fluid a mixture of gases (air) tiny liquid & solid particles (clouds, aerosols) Air obeys basic physical laws: Conservation of momentum Conservation of energy Conservation of mass Ideal gas law

How Modern Weather Forecasting Works (cont’d) Physical laws expressed mathematically: Nonlinear, coupled, partial differential equations for temperature, pressure, density, wind, and moisture

How Modern Weather Forecasting Works (cont’d) To solve the equations, in principle: Measure temperature, pressure, winds, moisture (weather observations) everywhere in the atmosphere at once (initial conditions) Integrate the equations from the initial time to any future time (the forecast)

How Modern Weather Forecasting Works (cont’d) Small Problem #1: We can’t measure the state of the weather everywhere at once! “Solution”: Measure everywhere we can and interpolate (i.e., make informed guess) in between Small Problem #2: The equations have no known exact solutions!

How Modern Weather Forecasting Works (cont’d) Solution: First, calculate solution only on a three-dimensional grid of points in space

How Modern Weather Forecasting Works (cont’d) Solution (cont’d): Second, calculate solution only at series of discrete times

How Modern Weather Forecasting Works (cont’d) Solution (cont’d): Third, approximate physical processes at grid points and interactions between neighboring grid points (finite difference approximations) The result: a numerical model Finally, use a computer to calculate future weather at discrete points in space and time (numerical weather forecast)

How Modern Weather Forecasting Works (cont’d) Small Problem #3: The basic equations are nonlinear, and small errors in initial conditions and small model errors grow over time (atmosphere is chaotic) Consequences: Currently can’t forecast detailed weather beyond 5-6 days Theoreticaly impossible to forecast detailed weather beyond ~ two weeks

The Public Perception:

How Modern Weather Forecasting Works (cont’d) Solutions: Make better weather observations (improve initial conditions) Make model grid points closer together (increase model resolution) These require new/improved technology

How to Make Better Weather Forecasts Improve the observed, initial conditions More accurate measurements Better geographic coverage Higher Resolution Measurements Increase model resolution

How to Make Better Weather Forecasts Improve the observed, initial conditions More accurate measurements Example: Temperature, pressure, moisture, and wind above the earth’s surface measured by radiosondes carried by balloons

Network of radiosonde launching stations; radiosondes launched twice daily, all at once

Radiosondes Winds are estimated by tracking the balloon with radar Can’t track through rain/snow storm Wind speed accuracy only ±10% Technology improvements: Attach Global Positioning System (GPS) Wind speed accuracy ± 0.5-5% GPS radiosonde receiver

Improve the observed, initial conditions Better geographic coverage Few direct observations over oceans, many Third World countries, Antarctica, etc. Technology improvements: Better satellite remote sensing GOES-West water vapor images

Improve the observed, initial conditions Higher resolution measurements Technology Improvements: Small, portable Doppler radar Can see inside severe thunderstorms & tornados

How to Make Better Weather Forecasts Increase numerical model resolution More grid points requires more calculations; limited by size/speed of computers Technology Improvements: Bigger, faster computers Supercomputers Use many computers at once (parallel, distributed processing) Supercomputer at the National Center for Atmospheric Research

Technology Solutions: Small Problem #4: More weather observations & more detailed numerical weather forecasts generate huge amounts of data to communicate, analyze, and display Technology Solutions: Better, faster internet Internet2 New analysis and display software Integrated Data Viewer