Atmospheric Variability

1. Atmospheric Variability • Why is it so cold winter 2010-2011? • Why was it so hot summer 2010? • Why was it so dry in 2007? • Why was it so wet in 1998, 2009 (fall)? • Are these extremes becoming more common? Why or why not? • Does variability in atmospheric flow patterns fully answer these questions?

2. Atmospheric Variability • Temporal • weekly, monthly, seasonal, annual, decadal • Spatial (x,y) • Global, synoptic, regional, mesoscale, microscale, sub-micro • Vertical (z) • Surface, 1000mb, 925, 850, 700, 500, 300 • Trends? • Natural or anomalous

3. What is a teleconnection • AMS: • 1. A linkage between weather changes occurring in widely separated regions of the globe. 2. A significant positive or negative correlation in the fluctuations of a field at widely separated points. Most commonly applied to variability on monthly and longer timescales, the name refers to the fact that such correlations suggest that information is propagating between the distant points through the atmosphere.” • Pressure fluctuations • SST • Height anomalies (700, 500mb) • Associations with circulation indices

4. The North Atlantic Oscillation (NAO) • Pressure dipole in North Atlantic centered near Iceland/Greenland and over the Azores • Icelandic Low vs Azores High • Tendency for either both weak or both strong • Dominant mode of Variability in Atlantic • Winter • The NAO index is obtained by projecting the NAO loading pattern to the daily anomaly 500 millibar height field over 0-90°N. The NAO loading pattern has been chosen as the first mode of a Rotated Empirical Orthogonal Function (EOF) analysis using monthly mean 500 millibar height anomaly data from 1950 to 2000 over 0-90°N latitude. (NCDC)

6. The North Atlantic Oscillation

7. The North Atlantic Oscillation Dec – March Temp correlations Dec – March Precip correlations

8. Bama state averaged temp Dec-Feb

10. Arctic Oscillation (AO) or NHam • Cyclonic circulation of upper level winds around the Arctic • Latitude poleward of 55°N • Positive = stronger winds- confines Arctic air • More zonal • Negative = relaxed winds- Arctic air oozes southward • AO index is obtained by projecting the AO loading pattern to the daily anomaly 1000 millibar height field over 20°N-90°N latitude

11. Winter AO

12. Bama state averaged temp Dec-Feb

13. Current Phase

15. Pacific North American (PNA) • Quadripole pattern of 500mb height anomalies • All months except June and July • winter • Center locations • Similar signs south of Aleutians and over SE U.S. • Hawaii and InterMountain U.S. and Canada • The PNA index is obtained by projecting the PNA loading pattern to the daily anomaly 500 millibar height field over 0-90°N. The PNA loading pattern has been chosen as the second mode of a Rotated EOF analysis using monthly mean 500 millibar height anomaly data from 1950 to 2000 over 0-90°N latitude.

17. PNA

18. Bama state averaged temp Dec-Feb

20. Current Phase PNA

21. El Nino Southern Oscillation (ENSO) • Both a SST and pressure fluctuation in the tropical Pacific • ~ 5-7 year periodicity • Most significant atmospheric/oceanic coupling in the world • El Nino = warmer than normal SST • La Nina = colder than normal SST • Southern oscillation= pressure flip-flop http://www.cpc.ncep.noaa.gov/products/analysis_monitoring/enso_update/sstanim.shtml

23. Southern Oscillation Index (SOI) • Standardized difference in MSLP between Darwin Australia and Tahiti (T-D) • Pressure normally higher over Tahiti and lower over Darwin • Slow east to west flow of tropical water

25. Nino Regions

26. Oceanic Nino Index • Running mean of the Nino 3.4 region • At least 5 consecutive overlapping months above (below) 0.5°C sst anomaly

28. ENSO Impacts

29. Alabama Impacts http://www.cpc.ncep.noaa.gov/products/precip/CWlink/ENSO/box_whiskers/index.php

30. Projected ENSO November 2012 – April 2014

31. Pacific Decadal Oscillation (PDO) • Discovered 1996 (Hare and Mantua) • Leading principal component of Northern Pacific SST variability • Similar to ENSO • Long-lived ENSO • Greater SST variability in mid latitiude Pacific

32. Pacific Decadal Oscillation (PDO) Positive Negative

33. El Nino vs positive PDO

35. Atlantic Multidecadal Oscillation (AMO) • Fluctuation in detrended SST in north Atlantic (0 – 70°N) • AMO index 10 year running mean • Relationships to speed of thermohaline circulation

36. Thermohaline Circulation

37. AMO and hurricane activity

38. AMO and hurricane activity

39. PDO and AMO drought

40. Quasi Biennial Oscillation (QBO) • Oscillating (E-W) stratospheric winds 10 – 100 mb above the equator • 20 – 36 month periodicity • Impacts • Spike in ATL hurricane activity during west (positive) zonal flow • May impact Asian monsoon and ENSO

41. Quasi Biennial Oscillation (QBO)

42. Madden Julian Oscillation • 30 – 60 day oscillation, Tropical Indo-Pacific • Eastward wave propagation of anomlaous rainfall low OLR • 4-8 m/s • Impacts trop and subtrop, precip, temp, and circulation • Most prominent NH winter • U.S. Impacts • Increase frequency/intensity west coast precip • Eastern cold air outbreaks • http://web.archive.org/web/20070612204448/http://www.apsru.gov.au/mjo/index.asp

43. Madden Julian Oscillation

44. MJO- OLR and pressure

45. MJO Phase Diagram http://www.cpc.ncep.noaa.gov/products/precip/CWlink/MJO/Composites/Precipitation/

46. MJO and Atlantic Hurricanes • Phase 1 and 2 support a more active regime of Atlantic convection • ACE > 76 • 91.5 major hurricane days (1974 – 2007) • Phase 6 and 7 less active • ACE < 36 • 20.5 major hurricane days (1974 – 2007)

47. Others not discussed • ESRL Indices • http://www.esrl.noaa.gov/psd/data/climateindices/list/ • Climate Prediction Center • http://www.cpc.ncep.noaa.gov/