Ming Cai Department of Earth, Ocean, and Atmospheric Science, Florida State University

1. Variability of Mass Transport into Polar Stratosphere and Winter Cold Air Outbreaks in Mid-latitudes Ming Cai Department of Earth, Ocean, and Atmospheric Science, Florida State University Acknowledgement: Huug M. van den Dool, Y-Y Yu, R-C Ren Grant Support: NOAA CPO: NA10OAR4310168

2. A hybrid forecasting strategy for intraseasonal cold season climate predictions (14 - 60? days) • Prognostic component: Dynamical prediction for (extratropic) stratospheric anomalies using CFS. Status: Zhang et al. (2013): Evaluation of CFSv2 Predictions for the Stratospheric Circulation Anomalies (see the poster on Wednesday and Thursday). • Diagnostic component: Statistical “instantaneous” relations between stratospheric and surface temperature anomalies (downscaling) Status:This presentation (manuscript under preparation) • Development of prototype forecast tools Status:waiting for availability of DAILY forecasts or reforecasts with lead time > 2 weeks and new funding

3. Mean meridional mass circulation in winter hemisphere (Cai and Shin 2014)

4. Vertical and meridional couplings by baroclinically amplifying (westward tilting) waves (Johnson 1989) • A net poleward (adiabatic) transport of warm air mass aloft and a net equatorward (adiabatic) transport of cold air mass transport below. • Stronger poleward air mass transport in the warm air branch aloft is coupled with stronger air mass transport in the cold air branch near the surface and vice versa.

5. Mass circulation variability and cold air outbreaks in the mid-latitudes Weaker Meridional Mass Circulation near surface Stronger Meridional Mass Circulation near surface 90N 90N Warm air Warm air 60N 60N Cold air Cold air 25N 25N Less cold air outbreaks in mid-latitudes Coldness in high latitudes More cold air outbreaks in mid-latitudes Warmness in high latitudes

6. Indices of mass circulation crossing the polar circle • WB60N: the total air mass transported into the polar region • CB60N: the total air mass out of the polar region WB60N and CB60N are nearly perfectly positively correlated. WB60N is representative mass circulation crossing 60N The results with n = 0 are representative

7. WH(t) and WM(t): Percentage of area occupied by positive temperature anomalies exceeding 0.5*standard_deviation (local) in high latitude zone (60 N poleward) and mid-latitudes (between 25 and 60N). Indices of coldness and warmness CH(t) and CM(t): Percentage of area occupied by negative temperature anomalies below 0.5*standard_deviation (local) in high latitude zone (60 N poleward) and mid-latitudes (between 25 and 60N). The constant of 0.3085 corresponds to the fractional area of a given domain occupied by SATA exceeding/below 0.5LSD. The results with n = 0 are representative

8. Data and Analysis Procedures • ERA Interim Daily fields of T_surf, p_surf, 3D air temperature and winds in winters from 1979-2011 (33 winters): winter = Nov. 1 – Feb. 28 (120 days) • Anomaly field = departure of the total field from the daily annual cycle. • 6 WB60N threshold values: (1) WB60N’ < -1.0SD (weaker circulation), (2) WB60N’ < -0.5SD (weak circulation); (3) -0.5SD WB60N’ < 0 (Neutral-); (4) 0<WB60N’< 0.5SD (Neutral+); WB60N’> 0.5SD (strong); and WB60N’> 1.0SD (Stronger) • Unless specified otherwise, all statistics of T_surf anomalies are obtained in the period of 1-10 days after WB50N reaches one of the threshold values.

9. High latitudes Coldness Warmness Lead/Lag Correlations between WB60N and warmness/coldness Indices Amp. Mid-latitudes Mass circulation

10. Shift of PDFs of temperature indices with WB60N Coldness ChighCmid-lat Warmness Weaker Stronger Weaker Stronger Warmness Whigh Wmid-lat Coldness Weaker Stronger Weaker Stronger

11. T > 0.5LSD T < -0.5LSD Weak Circulation Maps of Probability of T > 0.5LSD or T < -0.5LSD T < -0.5LSD T > 0.5LSD Strong Circulation

12. Neutral- Neutral+ Weak Circulation Strong Circulation Composite Mean Surface Temperature Anomalies Weaker Circulation Stronger Circulation

13. EOF1 13.1% EOF2 11.3% EOF3 8.4% EOF4 7.6% EOF modes of Surface Temperature Anomalies EOF6 4.8% EOF5 5.4% Sum=50.3%

14. Neutral- Neutral+ Weak Circulation Strong Circulation Contribution to the mean composite pattern Weaker Circulation Stronger Circulation

15. Composite Means of Time Series of EOFs Amp. Mass circulation

16. EOF1 EOF2 _______ Climatology EOF3 EOF4 _______ Strong Circulation Contribution to Variance of EOFs Amp. EOF6 EOF5 ________ Weak Circulation Mass circulation

17. Survey of mass circulation crossing 60N in winter of 2013-14 Stratosphere Warm Branch 1/18/14 12/9/13 1/1/14 Cold Branch 1SD climatology -1SD

18. Mean Ts 12/10-12/16 Mean Ts 1/2-1/7 Composite Means of Tsurf day 1-7 after Mean Ts 1/19-1/25 Mean of the three cases Amp. Mass circulation

19. Summary • Variability of mass flux warm air branch is synchronized with that of cold air branch. • Lack of warm air into polar region is accompanied by weaker equatorward advancement of cold air near the surface. As a result, the cold air mass is largely imprisoned within polar circle, responsible for general warmness in mid-latitudes and below climatology temperature in high latitudes. • Stronger warm air into polar stratosphere is accompanied by stronger equatorward advancement of cold air near the surface, resulting in massive cold air outbreaks in mid-latitudes and warmth in high latitudes. • EOF1 and EOF4 of T_surf correspond to warm Arctic and cold over the two major continents after a stronger mass circulation (PDF shift in response to mass circulation). • Positive phase of EOF2 represents warm Eurasian and cold N. America or vice versa. Amplitude of both positive and negative phases of EOF2 tends to increase after a stronger mass circulation (var. increase in response to mass circulation).