Variability of tropopause pressure and temperature in Northern Hemispheric winter was investigated based on CSEOF analysis of 20-yr (1989-2009) NCEP/NCAR daily reanalysis data. Physical and dynamical mechanisms of tropopause variability and its connection with stratosphere and troposphere were also studied by extracting evolutions of various physical variables from the ECMWF reanalysis interim daily data to be physically consistent with tropopause variability. Evolution of tropopause pressure in winter is nearly identical with that of 250-hPa PV on both seasonal and subseasonal time scales for each CSEOF mode; a strong correlation is observed between the variation of tropopause pressure and 250-hPa PV. Evolution of tropopause temperature variability is nearly identical with the 200-hPa air temperature variability.

Examination of stratospheric variability reveals that the seasonal component of 250-hPa PV is mainly controlled by upper-level air temperature anomalies in latitudes higher than 60°N and by upper-level geopotential height anomalies in lower latitudes. The seasonal component of 250-hPa PV anomaly, and henceforth tropopause pressure anomaly, is well reflected in the troposphere both in air temperature (correlation: 0.4-0.8) and geopotential height (correlation: 0.5-0.8) from 30°N to North Pole; tropospheric connection with the tropopause pressure variability is stronger in middle latitudes than in high latitudes in both variables.

High-frequency tropopause variability is easily traced in the troposphere with strong relationship between 250-hPa PV and other physical variables: correlation with temperature is ~0.7-0.8 at around 500 hPa level and with geopotential height is ~0.7-0.8 at around 300 hPa level. Correlation with other variables such as vertical velocity and specific humidity is also significant in the troposphere. Correlation with these variables, on the other hand, is negligible in the stratosphere above ~100 hPa. Thus, it appears that high-frequency undulations on or near the tropopause are fairly well observed in the troposphere but not in the stratosphere.

In summary, tropopause variability consists of two major components—low-frequency component with time scales greater than 10 days and high-frequency component with time scales less than 10 days. The low-frequency component appears to derive from upper-level stratospheric variability whereas the high-frequency component is associated with high-frequency undulations near or on the tropopause. The former is transmitted weakly to the troposphere whereas the latter is well traced in many variables in the troposphere.