PRECIPITATION BEHAVIOR AS MEASURED IN SITU

Transcription

1 PRECIPITATION BEHAVIOR AS MEASURED IN SITU BY AN ACOUSTIC DEPTH GAUGE (ADG) AND SIMULATED BY TWO REANALYSES MODELS, AT FLEMING GLACIER, ANTARCTIC PENINSULA JORGE F. CARRASCO Universidad de Magallanes, Avda. Bulnes 01855, Punta Arenas- Chile. ANDRÉS RIVERA 1,2,3 AND ANJA WENDT 1 1 Centro de Estudios Científicos, Avda. Arturo Prat 514, Valdivia Chile, 2 Centro Ingeniería de la Innovación, Avda. Arturo Prat 514, Valdivia Chile 3 Departamento de Geografía, Universidad de Chile, Portugal 84, Santiago, Chile

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3 Heigth The sonic range sensor was set up to measure every hour to ensure a complete year of accumulation record. However, after September the instrument was cover by snow. So good data go from 1 December 2007 to 30 August m 0.44 m 22 ~0.71 m 2 2 m 2 All data less than 01 m (below the instrument resolution), as well as, all extreme hourly variations were filtered out, and replaced by the value of the previous hour.

4 4.0 ADG accumulation/removal ADG accumulation/removal (m snow) ADG accumulation only (m w.e.) 1 ADG accumulation/removal 2 Dec Jan Feb Mar Apr May Jun Jul Aug 3 4

5 The hourly snow height measurements were compared with modelling data obtained from: The NCEP/DOE R-2 which is an improved version of the NCEP Reanalysis I model, with a temporal coverage from 4- times a day, with horizontal resolution of T62 (~210 km) and vertical resolution of 28 levels The Ex-CFSR model, which is a third generation of the reanalysis product, it has a temporal resolution of 1 hour and horizontal and vertical resolutions of T382 (~35 km) and L64, respectively. The concurrent precipitation time series were obtained for the nearest gridpoint to the AWS-FG location, at every 6 hours for the NCEP/DOE R-2 and every one hour for the Ex-CFSR.

6 ADG accumulation/removal ADG accumulation/removal (m snow) ADG accumulation only (m w.e.) 1 NCEP/DOE R-2 Ex-CFSR 2 Precipitation (m) Dec Jan Feb Mar Apr May Jun Jul Aug 3 4

7 ADG accumulation/removal ADG accumulation (m w.e.) ADG accumulation/removal (m snow) ADG accumulation only (m w.e.) 1 Precipitation (m) Dec Jan Feb Mar Apr May Jun Jul Aug NCEP/DOE R-2 Ex-CFSR 2 3 4

8 Spatial resolution of the NCEP/DOE R-2 and Ex-CFSR re-analysis simulation at 18 UTC 6 December 2007

9 ADG accumulation/removal ADG accumulation (m w.e.) ADG accumulation/removal (m snow) ADG accumulation only (m w.e.) 1 Precipitation (m) Dec Jan Feb Mar Apr May Jun Jul Aug NCEP/DOE R-2 Ex-CFSR 2 3 4

10 (1) 00 UTC 6 December 2007 (2) 12 UTC 24 January 2008 (3) 06 UTC 20 May 2008 (4) 12 UTC 21 June 2008

11 Following Knuth et al. (2010), the accumulation events were categorized in: snowfall, drifting snow, blowing snow and unknown events. The latter category occurred when the snow depth change was undetermined. For calculating the wind speed thresholds for blowing and drifting snow, it was adjusted the original values found by Li and Pomeroy (1997) to the height of the sensor at AWS-FG. Thus, blowing snow events were determined for wind speed 6.81 ms -1 and drifting events for wind speed 4 ms -1 and < 6.81 ms -1. Snowfall events were those accumulation hours with wind speed < 4 ms -1.

12 ADG accumulation/removal ADG accumulation/removal (m snow) ADG accumulation only (m w.e.) 1 Precipitation (m) Dec Jan Feb Mar Apr May Jun Jul Aug ADG snowfall (m w.e.) NCEP/DOE R-2 Ex-CFSR 2 3 4

13 Number and percentage of precipitation events simulated by the NCEP/DOE R-2 and Ex-CFSR reanalyses and comparison with the number of events registered by the ADG. Number of model precipitation events Number of ADG accumulation events Number of concurrent events % Model True simulation % Model False simulation NCEP/DOE R-2 EX-CFSR (6 h) (1 h) % ADG events simulated by the model % ADG events missing by the model Duration 34.3 ± ± 21.2 Maximum 156 h (~6.5 d) 98 h (~4.d)

14 Conclusions ADG instrument seems to be good one for measuring snow behavior (accumulation) in Antarctica, but the drifting/blowing snow still needs to be reviewed. Better temporal and spatial model resolution improve precipitation forecast; which is overestimated in the overall accumulation, but not in the number of simulated events.