The strength of the diabatic circulation of the stratosphere

Transcription

1 The strength of the diabatic circulation of the stratosphere Ed Gerber October 25, 2017 S-RIP and SPARC-DA workshop with Marianna Linz*, Alan Plumb, Marta Abalos, Florian Haenel, Gabriele Stiller, Douglas Kinnison, Alison Ming, and Jessica Neu

2 The idealized tracer age of air is used as a proxy for the overturning circulation stratosphere How long has this air been in the stratosphere? Rate of change of age + Transport = Source: 1yr/yr pole equator troposphere pole In steady state,

3 Mean age roughly reflects the pattern of circulation BDC Schematic Plumb 2007 Haenel et al. 2015

4 Age and the overturning circulation are only qualitatively similar Age of Air Residual Circulation τ AoA-Residual Circulation τ years years 4 Modified from Garny et al. 2014

5 Insight from the Leaky Pipe of Neu and Plumb 1999: Diabatic circulation is related to the latitudinal gradient in age. Isentropic mixing between upward and downward branches of circulation increases vertical gradient, but leaves gross horizontal gradient unchanged!

6 Insight from the Leaky Pipe of Neu and Plumb 1999: Diabatic circulation is related to the latitudinal gradient in age. Isentropic mixing between upward and downward branches of circulation increases vertical gradient, but leaves gross horizontal gradient unchanged! Key idea today: (1) Extend leaky pipe to 3-D diabatic circulation (2) Use satellite-based age measurements to quantify the circulation

7 Consider the steady-state case Statistical equilibrium: Integrate over the volume above an isentropic surface*: (1) Age flux Isentropic density Total mass *neglecting diabatic diffusion

8 Divide the surface into upwelling and downwelling regions stratosphere θ The mass flux, through each of these two regions must be equal. pole equator troposphere pole

9 Divide the surface into upwelling and downwelling regions stratosphere θ The mass flux, through each of these two regions must be equal. pole equator troposphere pole Upwelling mass flux Downwelling mass flux

10 Divide the surface into upwelling and downwelling regions stratosphere θ The mass flux, through each of these two regions must be equal. pole equator troposphere pole (2) Upwelling mass flux Downwelling mass flux

11 Combine equations (1) and (2) (1) (2) Upwelling age Downwelling age Linz et al. JAS 2016

12 The age difference is inversely proportional to the circulation strength (Age down Age up) = total mass above Θ / Total overturning flux through Θ Linz et al. JAS 2016

13 The age difference is inversely proportional to the circulation strength Age difference on a surface depends only on the strength of the mean circulation through that surface. Linz et al. JAS 2016

14 Ages from satellite SF 6 measurements from MIPAS Haenel et al Kovacs et al. 2017

15 N 2 O shows a compact relationship with age of air Balloon and aircraft measurements from 1990s Age from satellite N 2 O, using Andrews cubic Andrews et al Linz et al. Nat. Geo. 2017

16 Age from SF6, N2O, and model are quite different Age on the 500 K isentrope MIPAS SF6-age WACCM SF6-age GOZCARDS N2O-age WACCM ideal age Linz et al. Nat. Geo. 2017

17 Age difference shows that the theory holds in a realistic model Linz et al. Nat. Geo. 2017

18 The two data calculations agree closely where they both exist Total diabatic circulation strength Linz et al. Nat. Geo. 2017

19 The two data calculations agree closely where they both exist Total diabatic circulation strength Data-based estimate of stratospheric diabatic circulation strength: x10 9 kg/s at 460 K Linz et al. Nat. Geo. 2017

20 The two data calculations agree closely where they both exist, while reanalysis products vary Total diabatic circulation strength Data set MIPAS SF 6 -age 7.43 GOZCARDS N 2 O 7.17 WACCM 7.11 ERA-Interim 6.48 JRA MERRA K overturning (x10 9 kg/s) Linz et al. Nat. Geo. 2017

21 Because of potential high bias in the method, ERA-Interim is in the range calculated from the data Total diabatic circulation strength Data set MIPAS SF 6 -age 7.43 GOZCARDS N 2 O 7.17 WACCM 7.11 ERA-Interim 6.48 JRA MERRA K overturning (x10 9 kg/s) Linz et al. Nat. Geo. 2017

22 Trends in the diabatic circulation are less significant than trends in other measures (K) WACCM free JRA 55 ERA-I MERRA diabatic circulation trend (kg/yr/day) x10 13

23 JRA 55 ERA MERRA Interim 55 Pressure (hp Pressure (hpa) re (hpa) (K) (K) Pressure (hpa) Correlations 10 1of the interannual variability show that the 2 diabatic 30 circulation is more closely related to one metric JRA 55 MERRA Pressure (hpa) 30 w* vs w* M vs w* Q vs (K) (K) (K)

24 Summary Latitudinal age difference on isentropes is directly related to the diabatic circulation strength.

25 Summary Latitudinal age difference on isentropes is directly related to the diabatic circulation strength. Strength of the circulation has been characterized from data. ERA-Interim plausible; JRA 55 and MERRA are outside confidence interval! (K) MIPAS SF 6 GOZCARDS N 2 O JRA55 MERRA ERA-I WACCM overturning (kg/s) Tropical altitude (km)

26 Summary Latitudinal age difference on isentropes is directly related to the diabatic circulation strength. Strength of the circulation has been characterized from data. ERA-Interim plausible; JRA 55 and MERRA are outside confidence interval! The diabatic circulation behaves differently than the traditional residual vertical velocity, including in vertical structure and in trends (K) MIPAS SF 6 GOZCARDS N 2 O JRA55 MERRA ERA-I WACCM overturning (kg/s) 10 9 (K) WACCM free JRA 55 ERA-I MERRA diabatic circulation trend (kg/yr/day) x Tropical altitude (km)