Geoscience Reference
In-Depth Information
The client refreshes real-time observations cycled in 5 min from radars and AWS (automatic
weather stations) and provides real-time alerts (sounding, flashing) for indication of severe
weather events (meeting certain thresholds such as wind speeds or rainfall amounts). It also
provides an interactive tool for preparing, editing and issuing Nowcast and warning for
severe weathers
Based on quality control, a regional 3D reflectivity mosaic is produced by trying to fill the
gaps that are generated by terrain blockage or AP. Products such as vertically integrated
liquid (VIL) , echo top (ET) and COTREC winds are then derived. QPE algorithm involves
extraction of convective echoes from stratiform echoes by texture and horizontal gradient
properties. Different Z-R relations are used for convective rain and stratiform rain. COTREC
(continuous tracking radar echo by correlation) vectors are echo motion vectors that are
derived from moving radar reflectivity patterns through grid-to-grid cross-correlation and
then adjusted by a horizontal non-divergence constraint for hourly nowcasts of rainfall (Li et
al, 1995). This is blended with mesoscale numerical prediction model output for 2-3 hour
nowcasts.
SWAN provides real time verifications for storm tracking and reflectivity nowcasts. Storm
track errors are shown as distance differences between observed storm tracks and predicted
storm tracks (1h). Observed radar reflectivity are also verified against extrapolated
forecasted reflectivity.
Severe weather warnings can be prepared and issued through SWAN by graphical interface
by circling an area on the screen, clicking an icon and doing some minor wording (Fig. 19).
A web-based version of SWAN has been developed and deployed in Guangdong
Meteorological Bureau.
Fig. 19. A SWAN display showing cells/tracks (main screen), SCIT (bottom) and time
histories of critical parameters (right). There are similarities with WDSS, NinJo and CARDS
displays.
