Detection and Inventory of Intense Pyroconvection in Western North America using GOES-15 Daytime Infrared Data

Abstract

Intense wildfires occasionally generate fire-triggered storms, known as pyrocumulonimbus (pyroCb), that can inject smoke particles and trace gases into the upper troposphere and lower stratosphere (UTLS). This study develops the first pyroCb detection algorithm using three infrared (IR) channels from the imager on board GOES-West (GOES-15). The algorithm first identifies deep convection near active fires via the longwave IR brightness temperature, distinguishing between midtropospheric and UTLS injections. During daytime, unique pyroCb microphysical properties are characterized by a medium-wave brightness temperature that is significantly larger than that in the longwave, allowing for separation of pyroCb from other deep convection. A cloud-opacity test reduces potential false detections. Application of this algorithm to 88 intense wildfires observed during the 2013 fire season in western North America resulted in successful detection of individual intense events, pyroCb embedded within traditional convection, and multiple, short-lived pulses of pyroconvective activity. Comparisons with a community inventory indicate that this algorithm captures the majority of pyroCb. The primary limitation is that pyroCb anvils can be small relative to GOES-West pixel size, especially in regions with large viewing angles. The algorithm is also sensitive to some false positives from traditional convection that either ingests smoke or exhibits extreme updraft velocities. A total of 26 pyroCb events are inventoried, including 31 individual pulses, all of which can inject smoke into the UTLS. Six of the inventoried intense pyroCb were not previously documented. Near-real-time application of this algorithm can be extended to other regions and to next-generation geostationary sensors, which offer significant advantages for pyroCb and fire detection.

The Great Slave Lake PyroCb of 5 August 2014: Observations, Simulations, Comparisons With Regular Convection, and Impact on UTLS Water Vapor

“…The observations made by the A‐Train and the ARW model results indicate that lower stratospheric water vapor may be influenced by pyroCb activity, at least on short time scales. As recent studies have shown, these pyroCb events are a relatively common occurrence every season (Peterson, Fromm, et al, ). Given the radiative significance of this greenhouse gas in the UTLS, it is worth considering a larger research effort into understanding the net impact that these events may have.…”

“…Small absolute values ( BTD 3.0 °C) indicate optically thick clouds. This test was validated by Peterson, Fromm, et al () for use with pyroCb anvils, and the result of that test on the GSL pyroCb anvil yields a BTD 12 − 11 spread between −0.1 and +1.0 °C; well within the optically thick range. This result gives confidence that the warm daytime BT 3 values indicate an abundance of very small ice particles in the anvil.…”

“…Pyrocumulonimbus (pyroCb) events have been established as a regular phenomenon in the boreal summer that routinely penetrate the tropopause (Damoah et al, ; Fromm et al, ; Peterson, Fromm, et al, ). They typically form over large wildland fires in the middle to high latitudes on an annual basis and produce a plume composed of a mixture of biomass‐burning aerosols, gases, and cloud ice particles that otherwise would not be present in the upper troposphere/lower stratosphere (UTLS) in such abundance (Fromm & Servranckx, ).…”

Aerosol Absorption: Progress Towards Global and Regional Constraints

“…As the climate responses to absorbing aerosols change with altitude [77], the authors suggest that high altitude BrC lofted from biomass burning events should be further studied. This was for instance done by Peterson et al [78], who developed a satellite-based inventory for pyrocumulonimbus clouds, which can elevate smoke particles into the upper troposphere and even the lower stratosphere. Promisingly, they find good correspondence between combined BC and BrC absorption determined from merging aircraft observations with radiative transfer calculations, and that obtained from remote sensing results from Ozone Monitoring Instrument (OMI) at two wavelengths (see below).…”

The Primary Convective Pathway for Observed Wildfire Emissions in the Upper Troposphere and Lower Stratosphere: A Targeted Reinterpretation

“…Meteorological conditions favoring pyroCb development suggest that pyroCb activity can be expected every fire season in favored regions of the Northern Hemisphere (Peterson et al, ). Peterson et al (; hereafter P17) inventoried and discussed pyroCb activity observed across western North America in 2013.…”