Status: Finalised Material from: Linus, Jonny
1. Impact
15-16 and again 18-19 April saw extremely warm period (by Arctic standards) associated with the high pressure over northern Europe. This blocking high has allowed warm-moist air from the mid-latitudes up to the Arctic, where the German ice breaker Polarstern is frozen into the ice (due north of Svalbard) as part of the MOSAIC campaign. Between the 17th and the 19th the observed temperature from the ship rose from 18 to just above freezing, which is more than 20C warmer than average for the time of year. This was associated the arrival of a moist air mass from mid-latitudes and highlights the bimodal character of the Arctic climate at this time of year.
As part of the Year of Polar Prediction (YOPP) consolidation period, a targeted observing period (TOP) was during the event. The "target" was the moist-intrusion into the Arctic associated with the warm anomaly discussed above. As part of this the number of radiosondes from Polarstern was increased (in the central Arctic).
2. Description of the event
The plots below show analyses of MSLP and 6-hour precipitation forecasts from 14 April 00UTC to 20 April 00UTC every 24h.
The plots below show analyses of z500 (contour) and t850 (shade) from 14 April 00UTC to 20 April 00UTC every 24h. The first reached Polarstern north of Svalbard from south-east on 16 April and the second on 18 April from south-west.
The plot below shows time-series of observed 2-metre temperature from Polarstern.
3. Predictability
3.1 Data assimilation
The plot below shows observation statistics for sfc-850hPa temperature from Polarstern radiosondes. Note the increased number of sondes during the targeted observation period.
3.2 HRES
3.3 ENS
The plots below show the EFI and SOT for 2-metre temperature valid 19 April, with a narrow band of warm air north of Svalbard.
The plots below show the EFI and SOT for Integrated water vapour flux ("Atmospheric river") valid 19 April,
The plot below shows evolution of 2-metre temperature forecasts for the position of Polarstern (84.3N, 14.75E), valid for 19 April 12UTC. The plot includes ENS forecasts (Blue box-and-whiskers), HRES (red dot) and model climate (red box-and-whisker). The observation from Polarstern was -0.1C. The probability boundaries for the box and whiskers are (1-99, 10-90, 25-75 and median as dot). Large uncertainties was present in the medium-range, probably due to the relatively small scale of the warm air mass.
