Comparing Different Tropopause Estimates From High‐Resolution Ozonesondes

Since the tropopause was first identified, the quality and resolution of weather balloons has dramatically improved. NOAA Earth System Research Laboratories (ESRL) have provided high resolution and very high quality ozonesondes from eight locations: Fiji; American Samoa; Greenland; Antarctica; and several locations in USA (Hawai'i, Colorado, California and Alabama). These locations collectively cover polar regions, mid‐latitudes and tropics. Using this publicly archived data set, we studied the variability of the tropopause for all eight locations for one complete year (2016). Along with the standard estimates of the tropopause provided by NOAA ESRL, we developed four alternative tropopause definitions each based on changes in one of the following: (a) molar density; (b) temperature lapse rates; (c) water vapor content; (d) ozone content. These old and new tropopause definitions appear to hold over all eight locations—for all seasons and from the tropics to the poles. The cohesiveness between all five of these independent tropopause definitions is remarkable, although the NOAA ESRL estimates sometimes identify higher tropopause onsets than the other estimates. Therefore, each tropopause definition could potentially be used as proxies for other tropopause definitions. However, it also confirms that the troposphere/tropopause transition is a multi‐faceted physical and chemical phenomenon associated with more than just temperature changes. Finally, these high‐resolution results suggest that the original term “tropopause” might be a misnomer since they suggest increases in temperature lapse rate variability, rather than the “pausing” implied by lower resolution data or by lapse rates that are averaged over large distances. Plain Language Summary In the lower atmosphere (“the troposphere”), the temperature decreases with height. This is why it is colder on mountaintops. Since 1902, it has been known that higher up in the atmosphere, in the region near where commercial airplanes fly, temperatures remain relatively constant with height. This region is called “the tropopause.” In 1957, the World Meteorological Organization (WMO) defined the start of the tropopause in terms of a set of rules, that were complex, but designed to be applicable for all latitudes and seasons. However, these rules are often hard to implement and can give ambiguous results. So, other definitions have been developed for specific regions, such as the tropics, that are more straightforward a