WIVERN: A Mission Concept for Observation Global Winds, Clouds and Precipitation

by A. J. Illingworth, J.C. Nicol, A Battaglia, and R. Dhillon

1. This work describes work done in preparing a proposal for a satellite, WIVERN, that can measure global in-cloud winds, clouds and precipitation and was submitted in March 2018 in response to the EE10 call for Earth Explorer mission ideas.  The in-cloud winds would complement the clear air winds to be measured by the recently launched Aeolus satellite and improve predictions of severe weather events on the scale of 2-3 days rather than 4-5 days for Aeolus.  The global rainfall estimates would improve knowledge of the global hydrological cycle and the representation of precipitation within climate and weather forecasting models.  The verdict is expected on 21 September 2018.

2. WIVERN will fly a W-band (94GHz) Doppler and Polarisation diversity radar with a 2.9 m antenna rotating at 8 rpm from a 500km orbit and 800km swath measuring line of sight winds with an accuracy of better than 2 m/s, a vertical resolution of better than 1 km, a horizontal resolution of about 60 km and daily visits poleward of 50 deg.   WIVERN is low risk. It will have two transmitters, polarized H and V to achieve the Dopper capability, each with the same specification as the transmitter that has performed beyond expectation on the successful nadir-pointing CloudSat mission that has been providing global profiles of cloud occurrence and characteristics since its launch in 2006.  It will also provide the CloudSat products of global precipitation and cloud ice water content but with a forty-fold improvement in global coverage.

3.  In addition two scientific studies have been performed:

a)  Ground- based observation with a 94GHz radar have confirmed that rainfall rates can be measured accurately and without biases with the WIVERN radar configuration and have verified that any biases of WIVERN winds, introduced when there are  reflectivity gradients and wind shear across the radar pulse, are sufficiently small so that WIVERN winds can be used to adjust the winds in weather forecast models.  

b) Cloud observations from the Canadian field campaign with a WIVERN airborne radar demonstrator have been used to assess the performance of the WIVERN radar.  An end to end model that ingests forecast model variables, simulates the radar signals, and then retrieves the forecast model variables from the simulated raw radar signals has been used to predict WIVERN performance for estimating winds in a hurricane.