Intense heating by wildfires can generate deep, smoke-infused thunderstorms, known as pyrocumulonimbus (pyroCb), which can release a large quantity of smoke particles above jet aircraft cruising altitudes. Injections of pyroCb smoke into the lower stratosphere have gained increasing attention over the past 15 years due to the rapid proliferation of satellite remote sensing tools. Impacts from volcanic eruptions and other troposphere-to-stratosphere exchange processes on stratospheric radiative and chemical equilibrium are well recognized and monitored. However, the role of pyroCb smoke in the climate system has yet to be acknowledged. Here, we show that the mass of smoke aerosol particles injected into the lower stratosphere from five near-simultaneous intense pyroCbs occurring in western North America on 12 August 2017 was comparable to that of a moderate volcanic eruption, and an order of magnitude larger than previous benchmarks for extreme pyroCb activity. The resulting stratospheric plume encircled the Northern Hemisphere over several months. By characterizing this event, we conclude that pyroCb activity, considered as either large singular events, or a full fire season inventory, significantly perturb the lower stratosphere in a manner comparable with infrequent volcanic intrusions.

Abstract. This overview paper highlights the successes of the Ozone Monitoring Instrument (OMI) on board the Aura satellite spanning a period of nearly 14 years. Data from OMI has been used in a wide range of applications and research resulting in many new findings. Due to its unprecedented spatial resolution, in combination with daily global coverage, OMI plays a unique role in measuring trace gases important for the ozone layer, air quality, and climate change. With the operational very fast delivery (VFD; direct readout) and near real-time (NRT) availability of the data, OMI also plays an important role in the development of operational services in the atmospheric chemistry domain.

[1] The large solar storms in October-November 2003 caused solar proton events (SPEs) at the Earth and impacted the middle atmospheric polar cap regions. Although occurring near the end of the maximum of solar cycle 23, the fourth largest period of SPEs measured in the past 40 years happened 28-31 October 2003. The highly energetic protons associated with the SPEs produced ionizations, excitations, dissociations, and dissociative ionizations of the background constituents, which led to the production of odd hydrogen (HO x ) and odd nitrogen (NO y ). NO x (NO + NO 2 ) was observed by the UARS HALOE instrument to increase over 20 ppbv throughout the Southern Hemisphere polar lower mesosphere. The NOAA 16 SBUV/2 instrument measured a short-term ozone depletion of 40% in the Southern Hemisphere polar lower mesosphere, probably a result of the HO x increases. SBUV/2 observations showed ozone depletions of 5-8% in the southern polar upper stratosphere lasting days beyond the events, most likely a result of the NO y enhancements. Longer-term Northern Hemisphere polar total ozone decreases of >0.5% were predicted to last for over 8 months past the events with the Goddard Space Flight Center two-dimensional model. Although the production of NO y constituents is the same in both hemispheres, the NO y constituents have a much larger impact in the northern than the southern polar latitudes because of the seasonal differences between the two hemispheres. These observations and model computations illustrate the substantial impact of solar protons on the polar neutral middle atmosphere.

[1] Previous studies have suggested that there should be secular trends in polar mesospheric cloud (PMC) occurrence frequency and brightness on decadal timescales and that those trends would be strongest at the lowest latitudes of the PMC existence region. We have analyzed the 27-year PMC data set created from Solar Backscatter Ultraviolet (SBUV, SBUV/2) satellite instruments for long-term variations in albedo using three latitude bands (50°-64°, 64°-74°, 74°-82°). The improved version 3 data set includes revisions to the PMC detection algorithm to produce more consistent results in all measurement conditions. A detailed error analysis yields an approximate uncertainty of 1-2% for seasonally averaged 252-nm albedo values. Adjustments for local time variations in PMC brightness between different satellite data sets were derived to ensure accurate trend calculations. Multiple linear regression fits show that albedo variations are anticorrelated with solar activity in all latitude bands, with a stronger response at high latitudes. The albedo increase from solar maximum to solar minimum ranges from +2% at 50°-64°S to +17% at 74°-82°N. Secular trends in albedo are positive, with long-term changes over 27 years ranging from +12% to +20% depending on hemisphere and latitude. The derived long-term trend in PMC albedo at 50°-64°is smaller than that of higher latitudes. This result contradicts previous suggestions that PMC brightness changes might be most rapid at low latitudes. The albedo response to solar variations is larger in the Northern Hemisphere, while long-term trends are approximately the same in both hemispheres.Citation: DeLand, M. T., E. P. Shettle, G. E. Thomas, and J. J. Olivero (2007), Latitude-dependent long-term variations in polar mesospheric clouds from SBUV version 3 PMC data,

Previous satellite measurements have provided nearly complete seasonal and geographic coverage of polar mesospheric clouds (PMCs), but previous data sets have not been able to evaluate changes in PMC behavior on decadal timescales. The Solar Backscattered Ultraviolet (SBUV) series of ozone measuring instruments have been flying continuously since 1978. While the instrument design is not optimized for PMC detection, the radiance data can be analyzed to examine the occurrence frequency and intensity of relatively bright PMCs. In this paper, we present PMC results from five SBUV and SBUV/2 instruments covering more than 23 years (1978–2002), starting just before the maximum of solar cycle 21 and extending through the maximum of solar cycle 23. The overlapping data sets from nearly identical instruments give an accurate picture of long‐term variations. Multiple linear regression fits are used to examine solar and secular correlations. PMC occurrence frequency is anticorrelated with solar Lyman alpha irradiance, with an approximate 0.5‐year phase lag in the Northern Hemisphere (Rsolar = −0.87) and no phase lag in the Southern Hemisphere (Rsolar = −0.65). The distribution of cloud brightness by season appears to be changing over time. When the PMC brightness for each season is characterized using an exponential cumulative distribution function, the exponent decreases in magnitude by a factor of 2 from 1978 to 2002 in the Southern Hemisphere (Rtime = +0.85). This implies an increase in the relative proportion of the brightest PMCs. The secular brightness trend is less significant in the Northern Hemisphere (Rtime = +0.58). We discuss possible origins for these changes.