Tropopause-Penetrating Convection from Three-Dimensional Gridded NEXRAD Data

Abstract

A new method that combines radar reflectivities from individual Next Generation Weather Radars (NEXRAD) into a three-dimensional composite with high horizontal and vertical resolution is used to estimate storm-top altitudes for the continental United States east of the Rocky Mountains. Echo-top altitudes are compared with the altitude of the lapse-rate tropopause calculated from the ERA-Interim reanalysis and radiosondes. To sample the diurnal and annual cycles, tropopause-penetrating convection is analyzed at 3-h intervals throughout 2004. Overshooting convection is most common in the north-central part of the United States (the high plains). There is a pronounced seasonal cycle; the majority of overshooting systems occur during the warm season (March–August). There is also a strong diurnal cycle, with maximum overshooting occurring near 0000 UTC. The overshooting volume decreases rapidly with height above the tropopause. Radiosonde observations are used to evaluate the quality of the reanalysis tropopause altitudes and the dependence of overshooting depth on environmental characteristics. The radar–radiosonde comparison reveals that overshooting is deeper in double-tropopause environments and increases as the stability of the lower stratosphere decreases.

A case study of convectively sourced water vapor observed in the overworld stratosphere over the United States

“…Tropopause altitudes are then interpolated linearly in space and time to the higher resolution radar grid for comparison. The agreement between tropopause altitudes computed from ERA‐I and radiosondes is typically within ~500 m [ Solomon et al ., ; Homeyer et al ., ]. The fact that the MN‐WI storm system penetrated the local tropopause level frequently over the course of its lifetime is evident.…”

“…Climatological studies of convection focusing on CONUS, made possible by the development of the NEXRAD 3‐D, gridded, composite radar reflectivity data set, show that tropopause‐penetrating convection over this region has both a strong annual cycle and a characteristic geographic distribution [ Solomon et al ., ]. Solomon et al .…”

“…Solomon et al . [] evaluated maximum storm‐top altitudes at 3 h intervals for 1 year (2004) of composited NEXRAD data and determined the frequency, magnitude, and location of tropopause‐penetrating storms by comparison with the lapse‐rate tropopause determined from ERA‐I. They found that tropopause‐penetrating convection is most common in the north‐central part of the U.S. (the Great Plains) and that there is a pronounced seasonal cycle, with the majority of overshooting systems occurring between March and August.…”

“…As in Solomon et al . [], the geographic distribution of tropopause‐penetrating storms was found to favor the central U.S., with the very deepest storms (absolute altitude) occurring more frequently in June, July, and August. Though there is significant interannual variability in the number of overshoots detected, there are on average ~46,000 overshooting convective updrafts for the months March through August or ~250 per day that reach or exceed 1 km above the local tropopause level over the analysis region.…”

Enhanced stratospheric water vapor over the summertime continental United States and the role of overshooting convection

“…OTs are transient events with lifetimes typically less than 30 min, but they can exceed 1 hour in well-organized storms such as mesoscale convective systems and supercell storms (Bedka et al, 2015;Solomon et al, 2016 and the references therein). Animations such as the following show the variability in OTs sampled by GOES at 1 min of resolution: Infrared wavelength animation: http://cimss.ssec.wisc.edu/goes/srsor2015/ Visible wavelength animation: http://cimss.ssec.wisc.edu/goes/blog/wp-content/uploads/ It is clear that some OTs are quite persistent and are both prominent and detectable in IR imagery, but the majority of OTs in these particular animations are short lived (< 10 min).…”