Cross‐tropopause tracer transport in midlatitude convection

Abstract

[1] A three-dimensional cloud-resolving model is used to simulate the transport of lowertropospheric passive tracers into the lowermost stratosphere via midlatitude convection. In previous studies of troposphere-to-stratosphere convective transport the extent of irreversible transport is unclear because the tropopause location is difficult to determine in the highly perturbed environment directly above an active storm. To determine the irreversibility of cross-tropopause transport in this study, 10-hour simulations are carried out to cover the growth and decay cycles of the storm. After the decay of convection, isentropes relax to quasi-flat surfaces, and the position of the tropopause becomes much easier to establish. Air parcels containing boundary layer tracers were able to penetrate the stable stratosphere because diabatic processes increased the parcel's potential temperature sufficiently to make the parcel neutrally buoyant at stratospheric altitudes. The boundary layer tracer was carried upward in the core of the updraft whereas tracers originating from higher levels were lifted on the flanks of the updraft and therefore underwent less transport into the stratosphere. Three different cases were simulated: a prototypical supercell, a prototypical multicell, and a supercell observed during the Severe Thunderstorm Electrification and Precipitation Study (STEPS) field campaign. In the prototypical supercell simulation, at 1 km above the tropopause the maximum concentration of boundary layer tracer is diluted to 26% of its original concentration; the maximum concentration of the tracer originating in the layer between 1 and 4 km is diluted to 23% of its original concentration. Simulation of the STEPS storm showed similar irreversible transport in a less idealized case. Both supercell storms produced more transport than the prototypical multicell storm.

Modeling of biomass smoke injection into the lower stratosphere by a large forest fire (Part II): sensitivity studies

“…Due to the fire emissions of sensible heat, latent heat in the form of water vapor, and aerosol particles that can act as cloud condensation nuclei (CCN), pyroCbs have unique dynamic and microphysical structures. It is well established that severe convection is an important mechanism for troposphere-to-stratosphere transport in the midlatitudes (Wang, 2003;Mullendore et al, 2005). Similarly, pyroCbs can reach to the upper troposphere and lower stratosphere (UT/LS) (Fromm and Servranckx, 2003;Fromm et al, 2005).…”

Small-scale mixing processes enhancing troposphere-to-stratosphere transport by pyro-cumulonimbus storms

“…Even though mid-latitude deep convection accounts for only a small fraction of the air masses in the lowermost extra-tropical stratosphere (Holton et al, 1995), this process is very important for the budgets of many trace species in the lower stratosphere, most notably water vapor as well as some short-lived species (Mullendore et al, 2005). This is due to the rapid and direct transport from the planetary boundary layer, where most tracers have their sources.…”

“…Lane et al (2003) and Lane and Sharman (2006) found that the breakdown of gravity waves generated by thunderstorms is an important source of turbulence above the cloud and at tropopause level. Mullendore et al (2005) assessed the vertical transport of idealized passive tracers by deep convection and found that, in addition to latent heating, mixing processes contribute significantly to potential temperature increases necessary for irreversible TST.…”

Investigating the Impacts of Saharan Dust on Tropical Deep Convection Using Spectral Bin Microphysics, Part 1: Ice Formation and Cloud Properties

“…While the majority of ice and liquid hydrometeors are formed within the convective core, a significant amount of cloud mass is transported into the stratiform/anvil regime by upper level divergence and wind shear, where additional growth and particle collection may occur (Folkins, 2002;Mullendore, 2005). In addition, the actual contribution of the core to the total 25 cloud area compared to the stratiform/anvil regime is small, at ~1:7 (Liu and Fu, 2001) making consideration of dust effects on the stratiform regime important to the understanding of the large scale effects on the cloud fields reported in Min et al (2009) and Min and Li (2010).…”