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 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: NA10OAR

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 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 2 A hybrid forecasting strategy for intraseasonal cold season climate predictions ( ? days)

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

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.

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

6 Indices of mass circulation crossing the polar circle The results with n = 0 are representative 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 constant of corresponds to the fractional area of a given domain occupied by SATA exceeding/below 0.5LSD. 7 Indices of coldness and warmness The results with n = 0 are representative C H (t) and C M (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). W H (t) and W M (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).

ERA Interim Daily fields of T_surf, p_surf, 3D air temperature and winds in winters from (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’ 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. ERA Interim Daily fields of T_surf, p_surf, 3D air temperature and winds in winters from (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’ 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. 8 Data and Analysis Procedures

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

10 Shift of PDFs of temperature indices with WB60N Coldness Warmness Weaker Stronger W high W mid-lat Coldness Warmness C high C mid-lat

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

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

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

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

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

16 Contribution to Variance of EOFs Amp. Mass circulation EOF1 EOF5 EOF2 EOF6 EOF3EOF4 _______ Strong Circulation _______ Climatology ________ Weak Circulation

Survey of mass circulation crossing 60N in winter of Stratosphere Warm Branch Cold Branch climatology 1SD -1SD 12/9/131/1/14 1/18/14 17

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

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). 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). 19 Summary