Observations: Surface and Atmospheric Climate Change

• Surface Temperatures
• Statistical models developed to interpolate missing data
• Decadal scale and longer low frequency trends fit
• High frequency spatial-temporal covariance patterns estimated from data-rich periods
• Minor refinements tuned using simulated data
• Global average trends
• Large recent warming trend produces good matches between different processing methods
• Larger increases in nighttime minimum temperatures, particularly 1950-80
• Spatial patterns of trends
• Recent warming stronger at high northern latitudes
• Significant century scale warming trends widespread, recent more in NH
• Winter and spring warming of NH land masses large but not always significant
• Precipitation
• Higher interannual variability and more scatter between estimates
• Spatial patterns more complex than temperature
• Tropospheric temperatures
• Source of considerable contention
• Radiosonde vs satellite vs model
• Visual comparison looks fairly good
• Linear trend estimates rather variable
• Estimates using wind data from radiosondes
• Tropospheric wind data seem to have fewer artifacts than temperature data
• Thermal wind relationship vertical wind shear to horizontal temperature gradients
• Hydrostatic balance relates vertical height gradients to temperature
• Geostrophic balance relates horizontal winds to height gradients on constant pressure surfaces
• Mathematical details here
• Shear in zonal wind component allows determination of meridional temperature differences
• Need to know actual temperature at one latitude
• Not strictly applicable at the equator
• Tropospheric warming trends more consistent
• Better match with model predictions
• Trends in Extremes
• Difficult to deal with statistically but very important
• Global temperature and precipitation
• Temperature extremes show expected response to warming
• Precipitation shows slight increase in heavy precipitation events
• Fewer cold nights and more warm nights during last 25 years
• Decreasing trends in cold nights and days, increasing trends in warm, increase in % of precip from very wet days
• US precipitation extremes
• Increases in average over last century
• Appears to be increase in number of rain days, decrease in daily intensity
• Partly artifact of low recording of small totals in early period
• Trends less impressive for rain days > 0.05"
• Some areas in Midwest and Great Plains still show substantial increases in very wet days
• Hurricanes
• Measure of integrated hurricane energy closely matches recent ocean temperature increases
• North Atlantic shows doubling of energy
• Western North Pacific increases by 75%
• Combined North Atlantic and Western North Pacific nearly doubles
• Atmospheric Circulation Patterns and Teleconnections
• El Nino/Southern Oscillation (ENSO)
• Large coupled ocean/atmosphere oscillation
• Centered in tropical Pacific, but impacts ocean and atmosphere on near-global scales
• Irregular oscillation with 4-7 year time scale
• Also shows longer term variations in intensity and frequency
• Period of more frequent and intense warm ENSO events started with regime shift in 1977
• Somewhat predictable over periods of months to a few seasons
• Ocean/atmosphere interactions that produce growth in either phase are reasonably well understood and predictable
• Mechanisms that trigger switchovers from one phase to the other not well understood
• Pacific decadal oscillation (PDO)
• Define from coherent mode of North Pacific SST variability
• Shows longer term variability with regime shifts every 20-30 years
• Closely related to North Pacific index (NPI) which measures strength of the Aleutian Low
• Also inversely related to northern Indian Ocean temperatures
• Somewhat related to ENSO, but not completely
• Mechanisms not well understood
• Differences between the two phases
• Higher pressure in central Pacific (weaker Aleutial Low) during positive phase
• Precipitation decreases in Alaska, increases in Pacific Northwest, decreases in southern California
• Positive phase shows warmer air temperatures in western Pacific, cooler in eastern Pacific and western North America
• Very similar pattern for SST
• Appears to modulate the remote responses to ENSO variability
• North Pacific SLP patterns strong and consistent for El Nino/-NPI and La Nina/+NPI
• Deep 500mb trough over North Pacific for El Nino/-NPI, ridge for La Nina/+NPI
• North American surface temperatures
• North Atlantic Oscillation (NAO) and Northern Annular Mode (NAM)
• NAO defined by seesaw in SLP between northern and subtropical regions of Atlantic
• Produces substantial changes in temperatures and precipitation over eastern North America and Europe
• Shows considerable longer term variability
• Positive phase (strong Icelandic Low) associated with colder eastern Canada, warmer northern Europe
• Positive phase associated with increased precipitation in northern Europe, decreased in southern Europe
• Southern Annular Mode (SAM)
• Seesaw in pressure between Southern Hemisphere mid and high latitudes
• Shows a long term rising trend (deeper low over Antarctica, high in midlatitudes)
• Produces inverse temperature patterns over central Antarctica and Antarctic Peninsula
• Increased storminess in circumpolar trough
• Atlantic Multidecadal Oscillation (AMO)
• North Atlantic SST shows 60-80 year fluctuation
• Appears to be related to variations in strength of Atlantic thermohaline circulation
• Related to precipitation variations in West Africa, Caribbean, southern Europe, etc.
• Influences Atlantic hurricane formation
• Modulates impacts of NAO and ENSO