A Comparison of Arctic Cyclones between Periods of Low and High - - PowerPoint PPT Presentation

Kevin Biernat

Department of Atmospheric and Environmental Sciences University at Albany, SUNY

NEPARS Lightning Talk Wednesday 7 August 2019

A Comparison of Arctic Cyclones between Periods of Low and High Forecast Skill of the Synoptic-scale Flow over the Arctic

L1 AC12

(m s−1 ) 30 40 50 60 70 80 90 100 (mm) 25 30 35 40 45 50 55

0000 UTC 6 Aug 2012 300-hPa wind speed (m s−1, shaded); 1000–500-hPa thickness (dam, blue/red); SLP (hPa, black); PW (mm, shaded)

Arctic cyclones (ACs) are synoptic-scale cyclones that may originate within the Arctic or move into the Arctic from lower latitudes (e.g., Crawford and Serreze 2016)

Example: The Great Arctic Cyclone of August 2012 (AC12)

Data source: ERA5

Methodology

• Created a 2007–2017 climatology of ACs
• Determined low and high forecast skill periods over the

Arctic using GEFS reforecast dataset v2 and ECMWF Ensemble Prediction System

• Compared characteristics of Arctic cyclones and

synoptic-scale flow patterns associated with Arctic cyclones between low and high forecast skill periods

AC Track Frequency

Low skill (N = 401) High skill (N = 345) Total number of ACs within 500 km of a grid point, divided by number of days in period (number of ACs day−1)

0.005 0.01 0.02 0.03 0.04 0.05 0.06 0.08 0.1 0.12 0.14 0.16 0.18 0.2

AC Track Frequency Differences

Difference in AC track density (number of ACs day−1) Low skill minus high skill

0.01 0.005 0.02 0.03 0.04 0.05 0.06 0.08

• 0.005
• 0.01
• 0.02
• 0.03
• 0.04
• 0.05
• 0.06
• 0.08

Flow Amplitude

Arctic flow amplitude metric

low-skill mean high-skill mean shading: interquartile range 1979–2017 climo mean statistically significant difference between low/high skill mean and climo mean statistically significant difference between low and high skill means

Hours relative to 0000 UTC of low and high skill days

• 120
• 96
• 72
• 48
• 24

0.5 0.6 0.7 0.8 0.9 1.0 1.1 Anomalously amplified flow Anomalously deamplified flow