Observation strategies for severe rain in The Netherlands

Transcription

1 Observation strategies for severe rain in The Netherlands Herman Russchenberg Delft University of Technology Challenge the future

2 Our Earth is slowly warming

3 The world population is moving into the cities

4 and gets prone to severe weather

5 and gets prone to infrastructure infarcts

6 and gets prone to heat

7 and gets prone to air pollution

8 Gets prone does not have to mean will experience

9 The challenge is to make cities a nice place to live for 50 % of the world population summer, spring, autumn and winter

10 Climate change: What to expect in The Netherlands? Source: KNMI

11 Rainfall in a changing climate Higher temperature > more water vapour, warmer sea More rainfall and severe weather Observations during the 20th century: an increase of 20 % Predictions for the 21st century: more extreme rainfall in the summer more rainfall in the winter

12 Extreme rainfall in a metropolis Larger vulnerability modern society (flooding, transport, communication) Randstad: coastal urban conglomerate Accurate information needed Integrated model-observation warning systems Better understanding rainfall formation Detailed observations of microphysics needed Population: 7 million Economy: 4 th region of Europe Dense infrastructure

13 Philosophy: composite sat-lo-hi-res model to improve forecasts: street level hourly basis

14 The field laboratory: CESAR

15 IDRA TU Delft IRCTR Drizzle radar CESAR Cabauw Experimental Site for Atmospheric Research IDRA is mounted on top of the 213 m high meteorological tower. Specifications GHz central frequency FMCW with sawtooth modulation transmitting alternately horizontal and vertical polarisation, receiving simultaneously the coand the cross-polarised component 20 W transmission power µs µs sweep time 2.5 MHz 50 MHz Tx bandwidth 60 m 3 m range resolution 1.8 antenna half-power beamwidth Reference J. Figueras i Ventura: Design of a High Resolution X-band Doppler Polarimetric Weather Radar, PhD Thesis, TU Delft, (online available at Near real-time display: Processed and raw data available at: Courtesy Otto

16 Why FM-CW? Low transmit power Flexibility High resolution possible Solid state But: two antennas needed and more complex processing

17 High resolution rain observations DR= 30 m DR= 1 km File name: R /7-30-0Par Number of blocks: 143 Central Frequency: GHz Frequency Sweep: MHz Sweep time: us Transmitted power: W Polarization: Polarimetric Courtesy: KNMI

18 reflectivity (dbz) differential phase ( ) specific diff. phase ( /km) RDSD Nw (mm-1 m-3) differential reflectivity (db) diff. propagation phase ( ) diff. backscatter phase ( ) RDSD D0 (mm) A T M O S Examples of polarimetric X-band radar

19 Impact of polarimetry on estimation of rainfall rates No polarimetry Optimum use of polarimetry Courtesy Leijnse

20 35 GHz Courtesy Leijnse

21 Spectral-polarimetric classification Courtesy Durfournet

22 Development of rain: system plus meteorological model Ice and mixedphase cloud Melting layer Boundary layer echo drizzle rainfall Courtesy Durfournet

23 Concluding remarks Climate change leads to more severe weather Better forecasts of rainfall needed Explore feasibility of high-frequency, short range radars in cities Doppler-polarimetry gives details of microphysics and processes Combine with small scale, cloud resolving models Radar should be able to do without ground observations (truth?)