Infrequent, Rapid Transport Pathways to the Summer North American Upper Troposphere and Lower Stratosphere

Transport pathways from the Northern Hemisphere surface into the North American upper troposphere-lower stratosphere (NA UTLS) during summertime are diagnosed from Boundary Impulse Response idealized tracers implemented at the Northern Hemisphere surface. In ensemble average, air masses enter the NA UTLS region via deep convection above Central America, and then slowly mix into the higher latitudes. However, fast transport pathways with a modal age around two weeks are evident in some tracer ensembles. For these rapid transport pathways, the tracers first reach the UTLS region over the eastern Pacific and the Gulf of Mexico as a result of enhanced deep convection and vertical advection, followed by horizontal transport over the United States by a stronger than normal UTLS anticyclone circulation.