Atmospheric Responses to Solar Wind Dynamic Pressure

Transcription

1 Atmospheric Responses to Solar Wind Dynamic Pressure Hua Lu British Antarctic Survey

2 Outline Background: Sun-Earth Climate Connection Solar wind/geomagnetic activity signals with 3 examples stratospheric Quasi-Biennial Oscillation (QBO) the Northern Annular Mode (NAM) A non-linear relationship between geomagnetic activity and the North Atlantic Oscillation (NAO) Possible mechanisms

3 Motivation: Climate Change and Global Warming Large Uncertainty Is Associated with the Model Prediction Reduce uncertainty Better understanding natural vs human induced changes Predictions made by Intergovernmental Panel on Climate Change (IPCC)

4 Part I: Background: Sun-Earth Climate Connection

5 Natural Climate Variability Little Ice Age Frost Fair on the River Thames The Mer de Glace viewed from Montenvers, Mont Blanc region, French Alps, Swiss National Library

6 The Variable Sun The 11-year Solar Cycle and Solar Irradiance active sun quiet sun

7 The Sun Affects Earth s Atmospheric Temperature trends Detrended T T solar A lot of research has been done in this area But it is not the focus of this talk year (Lu et al. 2007, JGR)

8 Solar Wind and Energetic Particles Precipitation Corona Mass Ejection, most associated with proton precipitation Acknowledgement: the video clips are created by and downloaded from NASA Goddard Space Flight Centre Aurora activity is caused by high speed solar wind, most associated with electron precipitation and is affect by Sun s 27 day rotational periodicity

9 Solar Wind and Particle Precipitation particles precipitate into the Earth s atmosphere produce ionization from 150km down to ~40 km generate odd nitric oxide which may destroy ozone Solar wind and particles Protective magnetic field

10 Relevance to the Middle Atmosphere Energetic particles can penetrate to low altitudes where they drive changes in atmospheric chemistry Particle precipitation from the Earth s radiation belts could be very important for communicating solar variability to the Earth s middle atmosphere [e.g., Kozyra et al., AGU, 2006]. mesosphere stratosphere

11 Where particle precipitation occurs? Protons Protons Electro ns Electro ns Electrons tend to hit at mid- and high-latitudes Protons tend to fill the whole of the polar cap The effect of solar wind is mainly on the polar regions So the effect is more likely to be regional rather than global

12 Part II: Detecting solar wind signals in the atmospheric circulation variables

13 SW Dynamic Pressure vs the11-year Solar Cycle P sw =<N sw = sw ><V sw > cm F10.7 solar solar flux flux 300 Solar irradiance: 10.7-cm radio flux 250 (a) Solar wind dynamic pressure 2.5 (b) year SW dynamic pressure is not correlated with the 11- yr solar cycle since ~1990 They tend to be anticorrelated before 1985

14 A 11-year Solar Cycle within Solar Wind Dynamic Pressure 7 6 raw monthly data 36-mths highpass remaining low frequency 5 4 P sw (np) year

15 Example 1: Solar Wind Signal in the Stratospheric Quasi-Biennial Oscillation (QBO)

16 Example 1: Solar Wind Signal in the Stratospheric QBO 1 HP LP pressure levels (hpa) U (m/s) U (m/s) anomaly The solar wind dynamic pressure effect on the equatorial wind is of a three cell structure

17 Example 1: Solar Wind Signal in the Lower Stratospheric QBO 60 eqbo 70 hpa eqbo 50 hpa eqbo 30 hpa Occurrence (%) Easterly QBO occurred more often when solar wind dynamic pressure is high Occurrence (%) wqbo 70 hpa wqbo 50 hpa wqbo 30 hpa Opposite but small effect is found for the westerly QBO 20 J F M A M J J A S O N D J F M A M J J A S O N D J F M A M J J A S O N D Calendar Month HP LP

18 Example 1: Solar Wind Signal in the Stratospheric QBO (a) r = (98.75%) (n = 37) (b) (d) r = (99.1%) (n = 37) QBO 50hPa JASO (nt) P sw JASO QBO 30hPa JASO (nt) P sw JASO Negative correlation between SWDP and QBO The relationship is not dominated by either ENSO or major volcanic eruption affected years

19 Example 1: Solar wind Dynamic Pressure Signal in the equatorial wind and temperature U The signal is mainly associated with higher frequency component of solar wind Significant SW dynamic pressure signal in both U and T during Austral late winter and spring T Downward decent of the signals

20 Example 2: Solar wind Signal in the Northern Annular Mode (NAM) positive phase of NAM negative phase of NAM (From Jason Goodman)

21 Example 2: Solar wind Signal in the Northern Annular Mode (NAM) Stratosphere-Troposphere Coupling Baldwin and Dunkerton (2001): Science.

22 Example 2: Linear Correlation with 200 hpa NAM January-February mean NAM Jan-Feb (c) HS r = 0.8 (99.86%) n = Solar max P sw DJ (n m -1 s -2 x ) solar wind dynamic pressure Solar min (d) LS r = 0.16 (80.47%) n = P sw DJ (n m -1 s -2 x ) solar wind dynamic pressure 90 years in two digital number years in which stratospheric Sudden Warming occurred

23 Correlations with zonal-mean zonal wind and temperature Signals in January-February mean U Jan-Feb 60N 150hPa (m s -1 ) (a) r = 0.81 (99.8%) n = P sw, DJ (n m -1 s -2 x10 18 ) 93 T Jan-Feb 80N 200hPa (T) 8 4 (b) r = (99.79%) n = All years Solar max Solar min P sw, DJ (n m -1 s -2 x10 18 ) Zonal Wind (U) Temperature (T)

24 Downward progression of SW dynamic pressure signals Stronger and colder stratospheric vortex Poleward and downward propagation of westerly wind anomalies Downward movement of temperature anomalies Polar stratosphere is colder in mid-winter to late winter and warmer in spring

25 Example 3: Geomagnetic Signals in the North Atlantic Oscillation (NAO) From Daily Mail Online, 28 th of December, 2010

26 DJFM NAO Year U(t) & V(t) Year

27 U(t) & V(t)

28 Example 3: Geomagnetic Signals in the NAO , all data NAO DJFM (a) NAO DJFM (b) Geomagnetic aa DJFM Sunspot NO DJFM black line: the shaded region: General Additive Model (GAM) fitting 95% confidence interval

29 Example 3: Geomagnetic Signals in the NAO , GAM built from odd/even numbered solar cycles Rz DJFM (a) NAO DJFM (b) ( ) ( ) year aa DJFM NAO DJFM (c) NAO DJFM (d) aa DJFM aa DJFM

30 Example 3: Geomagnetic Signals in the NAO , the declining phase of even numbered solar cycles Rz DJFM (a) NAO DJFM (b) year aa DJFM ( ) ( NAO DJFM (c) NAO DJFM (d) aa DJFM aa DJFM

31 NAO DJFM (a) n = 42; R 2 = 0.34 (GAM); NAO DJFM (b) n = 6; R 2 = 0.22; p = 0.29 NAO = aa NAO DJFM aa DJFM (c) n = 20; R 2 = 0.15; p = 0.09 NAO = aa NAO DJFM aa DJFM (d) n = 15; R 2 = 0.59; p = NAO = aa 1969 Density aa DJFM aa DJFM aa

32 Part III: Possible mechanisms

33 Q: How does the solar wind dynamic pressure link to the NAM and weather? NAM index JF r = 0.74 (99.4%) P sw, DJ = <V sw > 2 <N sw > Solar wind dynamic pressure n = 18 Jan -Feb ) Wind 60N 14km -1 U (m s r = 0.81 (99.8%) n = 21 n = 18 Solar wind dynamic pressure 93 Jan -Feb Temperature 80N 12km n Jan = 18 -Feb r = (99.79%) Solar wind dynamic pressure 93

34 Production of Odd Nitrogen (NOx) by Energetic Particle Precipitation (EPP) Zonal averaged mixing ratio of (left) NO 2 and (right) O 3 at 80N from GOMOS data between 1 st January and 10 th March 2004 Hauchecorne et al. (2007) NOx ozone (Mixing ratio of NOx, Hartogh et al, JGR 2004)

35 Geomagnetic Impact on surface temperature Using ERA-40 reanalysis data to try to separate out the influence of solar UV variations and geomagnetic activity effects High Geomagnetic activity Low Geomagnetic activity High Low solar min condition solar max condition

36 What does this to do with the Aurora? A westward shift of the polar cell The signal becomes stronger at solar min and weaker at solar max

37 Speculative Mechanism wave-meanflow interaction Solar XUV EPP-NOx 0.01 hpa (82 km) 1 hpa (50 km) Mesopause Stratopause warm Solar UV? Westerly anomalies cold more gravity wave break near stratospause warm slower downward propagation under high solar activity faster downward propagation under low solar activity 100 hpa (12 km) Tropopause less planetary waves getting into the stratosphere cold Summer Equator Winter pole pole

38 Dynamic Characteristics of Solar Wind Disturbances to be confirmed by GCM studies and additional measurements Higher solar wind dynamic pressure favors the following dynamic responses: colder UM-LT polar region and warmer UM-LT equator region in mid-winter stronger westerly winds in the mesosphere sub-tropics and mid-latitudes less planetary waves propagating into the stratosphere from the troposphere slower Brewer-Dobson circulation lower stratosphere more gravity waves get into mesosphere stratopause a stronger and colder polar vortex in the more wave breaking near the breaking of gravity waves decelerates the westerly wind and creates a poleward meridional wind in the mid- to upper stratosphere a weaker, warmer polar vortex in the lower mesosphere and the upper stratosphere By continuity, the poleward wind induces a downward vertical wind in the polar region in late winter and spring. This downward motion is stronger in LS years than HS years due to the known effect of solar UV on the Brewer-Dobson

39 Summary