Transcript Papin_Poster_TropAMS16_v2x

P.33
Subtropical PV Streamer Variability and Impact in the Subtropical North Atlantic Basin
32nd Conference on Hurricanes and Tropical Meteorology
The Condado Hilton Plaza, San Juan, Puerto Rico
17-22 April 2016
1) Motivation
Philippe P. Papin*, Lance F. Bosart, Ryan D. Torn
Department of Atmospheric and Environmental Sciences – University at Albany: SUNY, Albany NY
Fig. 1. Example of a PV streamer. (a) 350-K PV (shaded, PVU) and winds (barbs, kt), (b) is 850 – 200-hPa vertical wind shear magnitude (shaded, m s-1) and direction
(barbs, kt), and (c) is precipitable water standardized anomaly (shaded, sigma) with the 40 mm contour overlaid.
 Upper-tropospheric potential vorticity (PV) streamers
are synoptic features resulting from Rossby Wave
Breaking (RWB) in the subtropical Atlantic Basin (Fig. 1a)
 These PV streamers modify the local environment by:
1.Enhancing vertical wind shear (VWS) corridors (Fig. 1b)
2.Enhancing moisture anomalies (Fig. 1c)
 These environmental factors influence tropical cyclone
(TC) activity in the Atlantic basin
 This study aims to investigate:
1.Seasonal PV streamer activity combining both their
size and intensity
2.How seasonal TC activity is modulated by seasonal PV
streamer activity
0000 UTC 9 Jun 2013
Fig. 4 (a) Time series of seasonal PV streamer count (blue line) and activity (red line, sigma x 104).
(b) 1 June – 30 November PV streamer frequency for 1994. (c) as in (b) except for 1995.
Fig. 3 1 June – 30 November PV streamer frequency (shaded, %) and
time-mean 200-hPa streamlines for the 1979 – 2014 climatology
High VWS
Fig. 2. (a) 350-K PV (shaded, PVU) with 2-PVU overlaid in black contour. (b) 350-K 2-PVU (blue contour) and points where a
meridional gradient reversal in PV is observed (red contour). (c) as in (b) except including area of PV streamer candidate (black
shading) with distances provided for the width, perimeter, and area of the PV streamer. (d) as in (c) except plotting
standardized PV anomaly (shaded, sigma) with the average PV anomaly of the PV streamer provided.
[σ]
Similar to Postal and Hitchman (1999)
 Highest PV streamer frequency occurs poleward of 20oN in the North Atlantic
and overlaps the location of the time-mean mid-ocean trough
 PV streamer activity integrated over area and intensity shows a trend towards
decreasing intensity since the 1980s despite only small changes in seasonal PV
streamer count
 Large year-to-year variance in PV streamer activity (Fig. 4b,c)
4) Impact on TC Activity
Points along contour where
meridional PV gradient
reversal is observed
Example: 0000 UTC 9 Jun 2013
Average PV Anomaly
+0.31 sigma
p must be three times w
p must be > 3000 km
3) Climatological Results
PV Streamer
2) PV Streamer Identification
Similar but more inclusive than Wernli and Sprenger (2007)
*Corresponding author e-mail:
[email protected]
Fig. 5. Scatter plot of PV streamer intensity metric
(sigma 104, x-axis) and ACE (kt2 104, y-axis), and their
linear regression (black line). Correlation coefficient
provided in the top right.
 Strong negative correlation (r = -0.62) between seasonal
accumulated cyclone energy (ACE) and PV streamer activity (Fig. 5)
 Composite 8 highest and lowest ACE years reveals decreases and
increases in PV streamer frequency basin wide in the subtropical
Atlantic (Fig. 6 a,b)
Fig. 6. Change in PV streamer
frequency (shaded, %) in (a) 8 highest
ACE seasons and (b) 8 lowest ACE
seasons.
p =12,823 km
[σ]
 Identification technique combines previous methodologies in order to link PV
streamer areas to RWB using the 0.5o Climate Forecast System Reanalysis (CFSR)
 Process:
o
o
o
1. Identify 2-PVU contour on 350-K surface from 0-70 N and 120 W – 20 E (Fig. 2a)
2. Identify points along contour where a meridional PV gradient reversal is
observed (Fig. 2b)
3. Calculate line orthogonal to first several points of PV reversal (Fig. 2c)
4. Check PV streamer is large & elongated using perimeter (p) and width (w)
5. Calculate the intensity of the PV streamer as a standardized quantity (Fig. 2d)
PVstd_anom = (PV – PVmean_climo) / PVstandard_deviation_climo
5) Conclusions
 PV streamers govern intensity and position of time-mean
mid ocean trough
 PV streamer activity inversely correlated with TC activity
 Future work will composite PV streamers of different
intensity and investigate their antecedent conditions
References
Postel, G. A., and M. H. Hitchman, 1999: A
Climatology of Rossby Wave Breaking
along the Subtropical Tropopause. J. Atmos. Sci.,
56, 359–373.
Wernli, H., and M. Sprenger, 2007: Identification and ERA-15
Climatology of Potential Vorticity Streamers and Cutoffs near
the Extratropical Tropopause. J. Atmos. Sci., 64, 1569–1586.