EG2234 Earth Observation Weather Forecasting

TOPICS Operational needs Operational constraints Remote sensing and weather Rainfall estimation TOPEX-Poseidon Modelling

Operational Needs Rapidly changing (dynamic) Regular instrumental updates (global) Dense coverage of stations Point to surface conversion (interpolate) Rapid dissemination to public Global, regional and local scales

ABOVE: moored buoy LEFT: drifting buoy

LEFT: radiosonde LEFT: launch of radiosonde balloon RIGHT: sounding rocket

Operational Constraints Locations of stations are often sparse No regular updates from inhospitable places (data retrieved from tapes) Large gaps in data – both spatial and temporal Collection of meteorological data requires access to Global Telecommunication System (GTS)

Global Station Coverage

Remote Sensing and Weather Geostationary satellites such as Meteosat provide high frequency data updates for a target region (15-30mins) Spectral channels on board the satellites yield useful information about position, direction and velocity of weather systems

Infrared radiant energy

Visible albedo

Water vapour Tropos. Water Cloud motion

AVHRR 29/11/01 13:39 < VIS IR >

Rainfall estimation Cold Cloud Duration (CCD) using Meteosat Tropical Rainfall Measuring Mission using radar (TRMM) Special Sensor Microwave Imager (SSM/I) rainfall measurement using microwave instruments

Pioneered by work of Lethbridge, 1967 Rainfall estimation Cold Cloud Duration (CCD): Pioneered by work of Lethbridge, 1967 Became an operational system thanks to Milford and Dugdale at TAMSAT (University of Reading) Based on relationship between period during which convective cloud tops are below a specific threshold and rainfall measured beneath them

Rainfall estimation Cold Cloud Duration (CCD): Convective clouds have a deep vertical structure. Cloud base height is usually uniform (flat bottomed clouds) Adiabatic cooling means that cloud becomes cooler with increasing height Colder cloud tops reveal a deeper structure = greater probability of rainfall

TRMM was launched in 1997 – with an initial mission life of 3 years Rainfall estimation Tropical Rainfall Measuring Mission (TRMM): TRMM mission is a joint US/Japan effort coordinated by NASDA (National Space Development Agency of Japan) TRMM was launched in 1997 – with an initial mission life of 3 years TRMM data is relayed to NASA Goddard Space Flight Center (GSFC)

TOPEX-POSEIDON For much of our oceans, temperature is not measured directly – but by proxy Warmer water expands – if surrounded by cooler water it rises. Its height is therefore an indication of its temperature

TOPEX-POSEIDON TOPEX is an altimetric satellite Return time of pulses of energy sent by TOPEX to the ocean surface are measured Distance between satellite and water surface can be accurately measured TOPEX used to measure El Niño

Modelling Because of serious gaps in station observations, satellite data supplements ground station, ship, buoy and ascent readings ALL data, once collected, is used to initialise climate prediction models Smooth gridded interpolated surfaces of observed data are called reanalysis

Modelling Reanalysis fields are generated for different pressure levels…from surface to 31 or so levels up to the top of the atmosphere

Modelling All spatially referenced meteorological data are processed at the Met. Office and fed into global climate models via the COSMOS system The current Unified Model (HadAM3) performs weather (short-range) and climate (long-range) forecasts

Modelling Weather and climate predictions generated by models are essentially thematic maps showing specific variables (rain, temperature, cloud etc.) All forecast field data are spatially referenced and can be easily fed into additional models (flood defence, agriculture, hydrology etc.)

The future Meteosat Second Generation is a new European weather satellite capable of observing Europe and Africa every 15 minutes Has more channels than the older Meteosat Can help resolve cloud physics parameters

The future Jason-1 is a new altimetric satellite designed to follow on from the T.POSEIDON mission