M. N. Ross

First measurements of the two‐dimensional horizontal wave number spectrum from CCD images of the nightglow

A narrow wavelength band CCD camera, built at Aerospace, has been used to obtain images of the OH Meinel (6,2) band and the O2 atmospheric (0,1) band nightglow. The field of view of the camera is approximately 100 by 100 km at an altitude of 90 km, the nominal height of the nightglow. It is shown how Fourier techniques can be applied to these data to optimally smooth the images, to identify the presence of monochromatic waves, and to obtain both the one-dimensional and, for the first time, the two-dimensional horizontal wave number spectrum of gravity waves passing through the emission layers. Both measures of the spectrum depend, to a certain extent, on a technique which makes use of Krassovskys η ratio. These techniques are applied to sample data taken from May 9, 1989, during the Arecibo Initiative in Dynamics of the Atmosphere (AIDA) campaign in Puerto Rico, and from the recent Collaborative Observations Regarding the Nightglow (CORN) campaign in Illinois. While future papers will describe these data in more detail, a brief comparison is made with recent models of the two-dimensional horizontal wave number spectra presented by Gardner et al. (1993) and Gardner (1994).

Observation of stratospheric ozone depletion in rocket exhaust plumes

Although modelling studies have predicted that particulate and reactive gas-phase species in the exhaust plume of large rockets might cause significant local ozone depletion, the actual response of the stratosphere after rocket launches has never been directly determined. Here we report comprehensive measurements that follow the evolution of stratospheric ozone in the wake of two Titan IV rockets launched on 12 May and 20 December 1996. In both cases, ozone concentrations dropped to near-zero values in the plume wake, across regions four to eight kilometres wide, within 30 minutes after launch; intense ozone loss persisted for 30 minutes after which time concentrations recovered to ambient levels. Our data indicate that the number of ozone molecules lost in the plume regions significantly exceed the number of chlorine molecules deposited by the two rockets. This suggests that a catalytic cycle based on Cl2O2, other than Cl2, and unique to solid rocket motor (SRM) plumes might be responsible for our observations. However, the limited spatial and temporal extent of the observed ozone losses implies that neither the catalytic Cl2O2 cycle nor other reactions involving exhaust compounds from large solid-fuelled rockets have a globally significant impact on stratospheric chemistry.

Observation of stratospheric ozone depletion associated with Delta II rocket emissions

Ozone, chlorine monoxide, methane, and submicron particulate concentrations were measured in the stratospheric plume wake of a Delta II rocket powered by a combination of solid (NH4ClO4/Al) and liquid (LOX/kerosene) propulsion systems. We apply a simple kinetics model describing the main features of gas-phase chlorine reactions in solid propellant exhaust plumes to derive the abundance of total reactive chlorine in the plume and estimate the associated cumulative ozone loss. Measured ozone loss during two plume encounters (12 and 39 minutes after launch) exceeded the estimate by about a factor of about two. Insofar as only the most significant gas-phase chlorine reactions are included in the calculation, these results suggest that additional plume wake chemical processes or emissions other than reactive chlorine from the Delta II propulsion system affect ozone levels in the plume.

The Active Temperature, Ozone and Moisture Microwave Spectrometer (ATOMMS)

The Active Temperature, Ozone and Moisture Microwave Spectrometer (ATOMMS) is designed to observe Earth’s climate. It extends and overcomes several limitations of the GPS radio occultation capabilities by simultaneously measuring atmospheric bending and absorption at frequencies approximately 10 and 100 times higher than GPS. This paper summarizes several important conceptual improvements to ATOMMS made since OPAC-1 including deriving the hydrostatic upper boundary condition directly from the ATOMMS observations, our much improved understanding of the impact of turbulence and its mitigation, and a new approach to deriving atmospheric profiles in the presence of inhomogeneous liquid water clouds. ATOMMS performance significantly exceeds that of radiometric sounders in terms of precision and vertical resolution and degrades only slightly in the presence of clouds and it does so independently of models. Our aircraft-to-aircraft occultation demonstration of ATOMMS performance will begin in 2009 representing a major step towards an orbiting observing system.

In-situ measurement of Cl2 and O3 in a stratospheric solid rocket motor exhaust plume

The concentration of Cl2 in the stratospheric exhaust plume of a Titan IV launch vehicle was measured with a neutral mass spectrometer carried on a WB-57F aircraft at 18.9 km altitude. Twenty nine minutes after a twilight Titan IV launch, the mean Cl2 concentration across an 8 km wide plume was 126 ± 44 ppbv, consistent with model predictions that a large fraction of the HCl in solid rocket motor exhaust is converted into Cl2 by afterburning reactions in the hot plume. Co-incident measurements with ultraviolet absorption photometers also carried on the aircraft show that ozone concentration in the plume was not different from ambient levels. This is consistent with model predictions that nighttime SRM launches will not cause transient ozone loss in the lower stratosphere. The measured Cl2 concentration equals 15% of the ambient ozone concentration suggesting that transient ozone reduction in SRM plume wakes can be expected after daytime launches when solar ultraviolet radiation will photolyze the exhaust plume Cl2.

Limits on the Space Launch Market Related to Stratospheric Ozone Depletion

Solid rocket motors (SRMs) and liquid rocket engines (LREs) deplete the global ozone layer in various capacities. We estimate global ozone depletion from rockets as a function of payload launch rate and relative mix of SRM and LRE rocket emissions. Currently, global rocket launches deplete the ozone layer ∼0.03%, an insignificant fraction of the depletion caused by other ozone depletion substances (ODSs). As the space industry grows and ODSs fade from the stratosphere, ozone depletion from rockets could become significant. This raises the possibility of regulation of space launch systems in the name of ozone protection. Large uncertainties in our understanding of ozone loss caused by rocket engines leave open the possibility that launch systems might be limited to as little as several tens of kilotons per year, comparable to the launch requirements of proposed space systems such as spaceplanes, space solar power, and space reflectors to mitigate climate change. The potential for limitations on launch systems due to idiosyncratic regulation to protect the ozone layer present a risk to space industrial development. The risk is particularly acute with regard to the economic rationale to develop low-cost, high flight rate launch systems.

In situ measurement of the aerosol size distribution in stratospheric solid rocket motor exhaust plumes

The concentration and size distribution of aerosol in the stratospheric exhaust plumes of two Space Shuttle rockets and one Titan IV rocket were measured using a two component aerosol sampling system carried aboard a WB-57F aircraft. Aerosol size distribution in the 0.01 µm to 4 µm diameter size range was measured using a two component sampling system. The measured distributions display a trimodal form with modes near 0.005 µm, 0.09 µm, and 2.03 µm and are used to infer the relative mass fractionation among the three modes. While the smallest mode has been estimated to contain as much as 10% of the total mass of SRM exhaust alumina, we find show that the smallest mode contains less than 0.05% of the alumina mass. This fraction is so small so as to significantly reduce the likelihood that heterogeneous reactions on the SRM alumina surfaces could produce a significant global impact on stratospheric chemistry.

Structure in the UV nightglow observed from low Earth orbit

Limb images of the low latitude UV O2 Herzberg I emission were obtained from a low Earth orbit spacecraft in early 1988. The layer displays patchy, sometimes horizontally periodic, spatial variability on scales of tens of km with amplitude up to 20%. We interpret periodic wavelike features in terms of perturbations associated with gravity wave propagation through the layer. The putative waves are shown to have horizontal wavelength about 15 km, similar vertical wavelength, and temperature oscillation roughly equal to or exceeding the observed emission perturbation.

Study blazing new trails into effects of aviation and rocket exhaust in the atmosphere

A new study may help resolve uncertainties in the impact of aviation and rocket exhaust on the atmosphere. Results of the project are expected to serve the aviation and rocket communities in their propulsion system choices and fleet operations in the 21st century. The study, known as the Atmospheric Chemistry of Combustion Emissions near the Tropopause (ACCENT) project, follows the lead of two other programs motivated by continuing concern over the impact such emissions are having on upper troposphere and lower stratosphere (UT/LS) ozone and climate. ACCENT in effect combines those two programs, one of which concerns aviation, the other rockets.

Radiative forcing caused by rocket engine emissions

Space transportation plays an important and growing role in Earths economic system. Rockets uniquely emit gases and particles directly into the middle and upper atmosphere where exhaust from hundreds of launches accumulates, changing atmospheric radiation patterns. The instantaneous radiative forcing (RF) caused by major rocket engine emissions CO2, H2O, black carbon (BC), and Al2O3 (alumina) is estimated. Rocket CO2 and H2O emissions do not produce significant RF. BC and alumina emissions, under some scenarios, have the potential to produce significant RF. Absorption of solar flux by BC is likely the main RF source from rocket launches. In a new finding, alumina particles, previously thought to cool the Earth by scattering solar flux back to space, absorb outgoing terrestrial longwave radiation, resulting in net positive RF. With the caveat that BC and alumina microphysics are poorly constrained, we find that the present-day RF from rocket launches equals 16 ± 8 mW m−2. The relative contributions from BC, alumina, and H2O are 70%, 28%, and 2%. respectively. The pace of rocket launches is predicted to grow and space transport RF could become comparable to global aviation RF in coming decades. Improved understanding of rocket emission RF requires more sophisticated modeling and improved data describing particle microphysics.