James M. Rosen

The Boiling Point of Stratospheric Aerosols

A photoelectric particle counter was used for the measurement of aerosol boiling points. The operational principle involves raising the temperature of the aerosol by vigorously heating a portion of the intake tube. At or above the boiling point, the particles disintegrate rather quickly, and a noticeable effect on the size distribution and concentration is observed. Stratospheric aerosols appear to have the same volatility as a solution of 75% sulfuric acid. Chemical analysis of the aerosols indicates that there are other substances present, but that the sulfate radical is apparently the major constituent.

Stratospheric Aerosol Measurements III: Optical Model Calculations.

Abstract : Articles in the literature dealing with light scattering properties of atmospheric aerosols are numerous and of great variety. Many fall into two general categories: those in which the effect of aerosols on radiative transfer processes in the atmosphere is studied, and those in which aerosol size distribution or composition information is obtained (or shown possible to be obtained) from light scattering measurements in the atmosphere. The results reported here, although limited to the stratospheric aerosol layer, are believed to be based on the most consistent and globally extensive measurements of the aerosol size distribution made to date. From this comprehensive set of data and other data on aerosol composition, the authors have constructed appropriate optical models which are used in Mie single-scattering calculations of the aerosol total extinction, absorption, 180 degree lidar backscattering, angular scattering, outward (2 pie hemispheric) scattering for a given solar zenith angle and finally, values of the global stratospheric aerosol albedo.

Pyro‐cumulonimbus injection of smoke to the stratosphere: Observations and impact of a super blowup in northwestern Canada on 3–4 August 1998

[1] We report observations and analysis of a pyro-cumulonimbus event in the midst of a boreal forest fire blowup in Northwest Territories Canada, near Norman Wells, on 3–4 August 1998. We find that this blowup caused a five-fold increase in lower stratospheric aerosol burden, as well as multiple reports of anomalous enhancements of tropospheric gases and aerosols across Europe 1 week later. Our observations come from solar occultation satellites (POAM III and SAGE II), nadir imagers (GOES, AVHRR, SeaWiFS, DMSP), TOMS, lidar, and backscattersonde. First, we provide a detailed analysis of the 3 August eruption of extreme pyro-convection. This includes identifying the specific pyro-cumulonimbus cells that caused the lower stratospheric aerosol injection, and a meteorological analysis. Next, we characterize the altitude, composition, and opacity of the post-convection smoke plume on 4–7 August. Finally, the stratospheric impact of this injection is analyzed. Satellite images reveal two noteworthy pyro-cumulonimbus phenomena: (1) an active-convection cloud top containing enough smoke to visibly alter the reflectivity of the cloud anvil in the Upper Troposphere Lower Stratosphere (UTLS) and (2) a smoke plume, that endured for at least 2 hours, atop an anvil. The smoke pall deposited by the Norman Wells pyro-convection was a very large, optically dense, UTLS-level plume on 4 August that exhibited a mesoscale cyclonic circulation. An analysis of plume color/texture from SeaWiFS data, aerosol index, and brightness temperature establishes the extreme altitude and ‘‘pure’’ smoke composition of this unique plume. We show what we believe to be a first-ever measurement of strongly enhanced ozone in the lower stratosphere mingled with smoke layers. We conclude that two to four extreme pyro-thunderstorms near Norman Wells created a smoke injection of hemispheric scope that substantially increased stratospheric optical depth, transported aerosols 7 km above the tropopause (above 430 K potential temperature), and also perturbed lower stratospheric ozone.

Balloon-borne observations of the development and vertical structure of the Antarctic ozone hole in 1986

A springtime deficit in Antarctic stratospheric ozone has been developing over recent years1,2. Here we describe the vertical distribution of ozone which was measured at McMurdo Station, Antarctica (78 °S), using balloon borne sensors, on 33 occasions during the period 25 August–6 November 1986. These observations suggest a highly structured cavity confined to the 12–20 km altitude region. In the 17–19 km altitude range, the ozone volume mixing ratio declined from about 2 p.p.m. at the end of August to about 0.5 p.p.m. by mid-October. The average decay in this region can be described as exponential with a half life of about 25 days. While total ozone, as obtained from profile integration, declined only about 35%, the integrated ozone between 14 and 18 km declined more than 70%. Vertical ozone profiles in the vortex revealed unusual structure with major features from 1 to 5 km thick which had suffered ozone depletions as great as 90%.

Stratospheric Aerosol Measurements I: Time Variations at Northern Midlatitudes

Abstract The results of over 70 balloon soundings, by the University of Wyomings Atmospheric Physics Group mostly during 1972 and 1973 from a number of stations, are being utilized in a study of the temporal and spatial distribution of the global stratospheric aerosol. This paper deals with the instrumentation, calibration, etc., and with the results of monthly soundings from the Laramie (41°N) station during the approximately two-year period of measurement. This period comprises an interval apparently free of major volcanic activity just prior to the extensive volcanic contributions to the stratospheric aerosol which occurred in late 1974. It thus may be compared to the pre-Agung era and is perhaps as close to the so-called “natural stratospheric background conditions,” if indeed such conditions ever exist, as will likely be attained in the near future. A simple seasonal variation in the total stratospheric aerosol loading below about 20 km altitude dominates the temporal variation at Laramie, resulting...

Backscattersonde: a new instrument for atmospheric aerosol research

A relatively simple balloonborne device for measuring the local aerosol backscatter at multiple wavelengths has been developed and field tested. The instrument produces detailed profiles which are inherently similar to those generated from lidar soundings. It is also sensitive, being able to measure the 20-km stratospheric aerosol background layer with a signal-to-noise ratio of approximately 100:1. An important feature of this device is its ability to be calibrated in an absolute sense. Theoretical considerations show that the measurements can be accurately converted to aerosol mass loading in the stratosphere for conditions ranging from background to heavy volcanic influence. The instrument is not expected to replace other observational techniques; rather it provides highly complementary information as well as furnishes a cost-effective alternative to measurement systems available to only a few scientists.

Stratospheric Aerosol Measurements II: The Worldwide Distribution

Abstract Global surveys of stratospheric and upper tropospheric aerosols have been made using balloon-borne photoelectric particle counters. The natural variability observed at each flight station was small enough so that typical profiles could be identified. Data are presented in the form of latitude cross sections showing lines of constant aerosol mixing ratio. The stratospheric aerosol layer is clearly delineated as well as small transient layers in the troposphere and lower stratosphere. At high and low latitudes the aerosol mixing ratio profile apparently experiences a simple shift in altitude corresponding to the change in local tropopause height.

Temperature histories in liquid and solid polar stratospheric cloud formation

Polar stratospheric clouds (PSCs) have been observed by balloonborne backscatter sondes from Alert, Thule, Heiss Island, Scoresbysund, Sodankyla, Sondre Stromfjord, and Ny Alesund during winters 1989, 1990, 1995, and 1996 in 30 flights. The observations can be categorized into two main groups: type 1a and type 1b PSC particles. Type 1b PSCs show the characteristics expected from liquid ternary solution (HNO3/H2SO4/H2O) particles, consistent with model simulations. Type 1a PSCs are observed at all temperatures below the condensation temperature TNAT of nitric acid trihydrate (NAT), consistent with solid NAT composition. Air parcel trajectories have been calculated for all observations to provide synoptic temperature histories of the observed particles. A number of cases have been identified, where the particles have experienced temperatures close to or above the sulfuric acid tetrahydrate melting temperatures within 20 days prior to observation. This assures a knowledge of the physical phase (liquid) of the particles at this time, prior to observation. The subsequent synoptic temperature histories, between melting and the time of observation, show pronounced differences for type 1a and type 1b PSC particles, indicating the qualitative temperature conditions, necessary to generate solid type 1a PSCs. The temperature histories of type 1b particles show smoothly, in most cases monotonie, decreasing temperatures. The temperature can apparently decrease to the frost point without causing the particles to freeze. The type 1b PSC particles are mostly observed shortly after entering a cold region. The observed type 1a particles have spent several days at temperatures close to or below TNAT prior to observation, often associated with several synoptic temperature oscillations around TNAT, and the particles are observed in aged clouds. It appears that the PSC particles may freeze, if they experience synoptic temperatures below TNAT with a duration of at least 1 day, possibly accompanied by several temperature oscillations. However, liquid particles that experience a smooth cooling, even to very low temperatures, or single smooth cooling/heating below TNAT without synoptic temperature fluctuations do not seem to freeze.

Optical modeling of stratopheric aerosols - Present status

A stratospheric aerosol optical model is developed which is based on a size distribution conforming to direct measurements. Additional constraints are consistent with large data sets of independently measured macroscopic aerosol properties such as mass and backscatter. The period under study covers background as well as highly disturbed volcanic conditions and an altitude interval ranging from the tropopause to approximately 30 km. The predictions of the model are used to form a basis for interpreting and intercomparing several diverse types of stratospheric aerosol measurement.

Decay of Mount Pinatubo aerosol at midlatitudes in the northern and southern hemispheres

Conjugate in situ observations of the stratospheric aerosol following the 1991 Mount Pinatubo eruption were made over Laramie, Wyoming (41°N), and Lauder, New Zealand (45°S), using balloon-borne backscattersondes. The results show similar aerosol loading and decay rates occurring over both midlatitude locations. A comparison with the 1982 El Chichon eruption as observed over Laramie indicates only somewhat higher mass mixing ratios for the Pinatubo eruption and very similar decay rates. As in the past, a strong correlation between local tropopause pressure and stratospheric aerosol mass loading was observed at the stations involved. Such a feature would be potentially useful for putting local measurements into a global prospective.