As the Winter Olympics come to a close this weekend, NASA/SPoRT continues its involvement in the International Collaborative Experiments for PyeongChang 2018 Olympic and Paralympic Winter Games (ICE-POP) through the gathering of field campaign observations and numerical weather prediction (NWP) model data. The ICE-POP campaign extends through March to support the Paralympic Games, and obtain more event data to set the stage for future research activities. During the first week of the 2018 PyeongChang Winter Olympics, another weather event worth highlighting is the shallow snow and high wind episode that disrupted downhill skiing competition at Jeongseon Hill on 14 February. On this day, a potent shortwave trough embedded in strong northwesterly flow approached the Korean Peninsula (Fig. 1), which led to a relatively short-lived, but potent snow event accompanied by strong winds in the mountains, occurring mainly between 0000-0600 UTC 14 February.
Figure 1. Animation of NASA Unified-WRF model 3-hourly 500-mb geopotential height (dam) and wind speed (m/s), valid between 1200 UTC 13 February to 1200 UTC 14 February 2018.
An animation of Himawari 10.4-micron infrared imagery from 1200 UTC 13 Feb to 1200 UTC 14 Feb (Fig. 2) shows enhanced cold cloud tops northwest of the Korean Peninsula associated with the shortwave. However, between 0000-0600 during the snow event, we see relatively warm cloud top temperatures over the Korean Peninsula, indicative of the shallow nature of the snow. Himawari visible imagery between ~0000-0800 UTC 14 February (Fig. 3) shows the presence of the low clouds that dissipate rapidly in coverage after 0600 UTC. Experimental ICE-POP disdrometer measurements of hydrometeor size distribution confirm the timing of the snow event between 0000-0600 UTC (Fig. 4), showing predominantly small diameter hydrometeors (most likely snow). However, the vertical “spikes” seen in Figure 4 between 0000-0200 UTC indicate some larger diameter snow aggregates associated with the more intense snow activity. Cloud profiling radar data (not shown) confirmed a shallow a nature to the precipitation, generally under 2 km depth.
Figure 2. Animation of Himawari 10.4 micron infrared imagery between 1200 UTC 13 February and 1200 UTC 14 February 2018.
Figure 3. Animation of Himawari visible imagery between 0000 and 0800 UTC 14 February.
Figure 4. Experimental ICE-POP distrometer measurements, showing the concentration and size distribution of hydrometeors as a function of UTC hour on 14 February 2018.
The experimental NASA Unified-Weather Research and Forecasting (NU-WRF) model simulations being provided to South Korea during the Olympics captured this event fairly well. Simulated composite radar reflectivity on the 1-km nested grid from the 1200 UTC 13 February model initialization (Fig. 5) shows a region of enhanced precipitation occurring between ~0000 to 0600 UTC 14 February, around the time of the observed snowfall. The experimental NU-WRF run also depicts strong 10-m wind speeds during this time (orange shades exceeding 20 m/s, or ~45+ mph), particularly along the axis of higher terrain in the eastern Korean Peninsula (Fig. 6). Finally, a time-height cross section of the NU-WRF simulated precipitation microphysics at Jeongseon Hill (Fig. 7) shows the precipitation episode timed between ~0000-0600 UTC 14 February, quite consistent with observational data. The model also captured the shallow nature of the event, with the most substantial snow and graupel mixing ratios being primarily at or below ~1500 m above ground.
The combination of these experimental observations and NWP model data being collected during the Winter Olympics will serve as a foundation for future research to improve our understanding of snow processes in complex terrain. Additionally, hydrometeor size distribution data from Fig. 4 along with other observations can help refine NWP model microphysical parameterization schemes to determine the proper distribution of precipitation species produced by the model.
Figure 5. SPoRT/NU-WRF simulated composite radar reflectivity (dBZ) every 30 minutes on the 1-km nested grid centered on the ICE-POP Olympics venues, for the model run initialized at 1200 UTC 13 February 2018. Valid times are from 1200 UTC 13 February to 1200 UTC 14 February.
Figure 6. Same as in Fig. 5, except for the maximum 30-minute interval 10-meter wind speeds.
Figure 7. Time-height cross section of SPoRT/NU-WRF model simulated precipitation mixing ratios (g/kg) from the 1-km nested grid, valid between 1200 UTC 13 Feb and 1200 UTC 14 Feb 2018 at the Jeongseon Hill Olympics site for the lowest 2 km above ground.