Earth's Radiation Budget

Approximately every two weeks, we are launching small meteorological balloons carrying compact, lightweight instruments to measure vertical profiles of water vapor, ozone, and aerosol number and size distribution from the surface to the middle stratosphere (~28 km). These measurements are being used to characterize the background state and variability of radiatively important aerosols in Earth's stratosphere. After a strong volcanic eruption or intense wildfire that injects material directly into the stratosphere, the measurements will help us to better understand how these natural events alter stratospheric composition, especially the number and size distribution of aerosols, and how these perturbations evolve with time.

In situ measurements of critical reactive species in the stratosphere are required to understand the heterogeneous chemistry that occurs on stratospheric aerosols to activate gas-phase halogen species, leading to catalytic destruction of ozone. There are only limited measurements available above 14 km of a number of these key gas-phase nitrogen containing species, such as chlorine nitrite (ClNO₂) and dinitrogen pentoxide (N2O5). Measurements of important species in the resulting ozone destruction chemistry, such as chlorine (Cl₂) and chlorine monoxide (ClO), are equally sparse. Measurements constraining the abundances of these species is critical for accurate modeling of stratospheric reactive halogen production and its subsequent impacts on stratospheric ozone destruction. A custom chemical ionization time-of-flight mass spectrometer is being developed to provide the capacity for accurate, precise in situ quantification of these key gas-phase species and more in the upper troposphere and lower stratosphere. Measurements from this instrument will provide us with the means for evaluating halogen activation during stratospheric aerosol perturbations resulting from volcanic eruptions or future stratospheric solar radiation management research and/or testing. Measurements of a range of gas-phase species deeper in the stratosphere using the instrument are expected to produce new insights into chemical processes occurring in the region.

One of the primary features of stratospheric aerosols is the so-called Junge Layer. This is a layer between roughly 20 and 25 km altitude in the tropics where the aerosol mass mixing ratio reaches a local maximum. Carbonyl sulfide (OCS) is the primary source of gas-phase sulfur that oxidizes in the stratosphere forming the sulfate-based Junge layer. In this project we will develop the capability to measure in-situ OCS from aircraft, allowing for these measurements to be performed on future research flights using aircraft such as the NASA WB-57F. Carbon monoxide (CO) is a product of combustion and atmospheric oxidation. It has a relatively short lifetime in the stratosphere making it a useful indicator of air that has recently been transported from the surface. OCS and CO can be simultaneously measured precisely and specifically using a single laser-based instrument that is available commercially. We plan to use such an instrument to provide measurements addressing multiple scientific objectives. These measurements will allow us to address a few key aspects to understanding stratospheric aerosols: (1) sources of stratospheric OCS, (2) age of air in the stratosphere and its relationship with aerosol composition and size distributions, (3) influence of convection and anthropogenic emissions on perturbing stratospheric composition.

Aerosol particles in the stratosphere reflect sunlight and cool the Earth, while also providing surfaces for chemical reactions that affect the stratospheric ozone layer. These processes depend strongly on the size of the particles and their abundance. We are improving our ability to measure the size and concentration of aerosol particles in the stratosphere – whether natural or man-made – by adapting a newly developed commercial instrument to the rigors of flight in the cold, low-pressure stratosphere and by carefully calibrating it and evaluating its performance. The instrument will be test-flown on a low-altitude aircraft and, if it works well, a backup instrument purchased and modified.

Rebuild the PALMS Counterflow virtual impactor inlet, a specialized inlet that can sample cirrus clouds to isolate the ice nuclei responsible for cloud formation.

A proposed method of climate intervention calls for the frequent injection of aerosol into the stratosphere to limit the penetration of solar radiation into the Earth's lower atmosphere and onto the Earth's surface. Aerosol composed of materials other than sulfate, e.g. calcite (CaCO₃, limestone), are being proposed to have a potentially lesser impact on stratospheric ozone. The chemical properties of calcite under stratospheric conditions are, however, presently not well-established, which results in substantial uncertainties in climate forecast model calculations. An objective of the present research is to evaluate the chemical properties and transformations of calcite under stratospheric conditions.

This project aims to determine what happens to the Earth's climate, from the surface up to the top of the stratosphere, when the climate intervention method termed Solar Aerosol Injection (SAI) is employed. An ensemble of model runs that allowed greenhouses gases to increase while introducing enough SO2 into the stratosphere to keep 3 specific surface temperature metrics at 2020 levels is analyzed to assess what the changes in circulation are. Topics specifically addressed include impacts on the ozone layer, transport between stratosphere and troposphere, and regional changes in temperature and precipitation at the surface.

This project has two components. The first is to determine what the impact of increasing rocket traffic will be on the stratosphere in regards to increases in soot loading. The second is to model the radiative forcing, temperature and circulation changes in the stratosphere due to increased aerosol loading from volcanic eruptions. Both components will use a global scale chemistry/climate model to assess the aerosol impacts.

The goal of this project is to improve the representation of the lifecycle processes and distribution of stratospheric sulfur aerosols in the NOAA GFDL's Earth System Model. Specifically, the model is updated to simulate stratospheric sulfur loading and aerosol optical properties driven by volcanic and non-volcanic sulfur emissions. This improvement enhances the capability of the model to assess the effects of naturally and artificially injected stratospheric sulfur aerosols on stratospheric chemistry and Earth's radiation budget.

This project aims to achieve an enhanced understanding of atmospheric aerosol processes and resulting feedbacks to the climate system through the inclusion of a sophisticated aerosol representation into a leading Earth System model. The new developments will be tested against available observations for periods of low and high aerosol levels in both the troposphere and stratosphere. This model configuration will serve as a benchmark model for simpler aerosol representations. After completion, this configuration will be made available to the community and will enable various new research opportunities and further model developments moving forward. This project will increase modeling skill available to the US and world scientific communities to examine the current state of the atmosphere, as well as multiple proposed scenarios of climate intervention strategies including stratospheric aerosol perturbations.

Traditional thinking anticipates that an injection of particles into marine boundary layer clouds will create more numerous, smaller cloud droplets, leading to clouds that reflect more solar energy back to space, and a cooling of the planet. Our work unveils both expected responses as well as the possibility of inadvertent responses that might result in reduction rather than enhancement in cloud reflectance. The project aims to map out a broad range of possible responses that will give a better quantification of the extent of brightening in natural clouds. To this end we use a combination of novel numerical modeling tools and statistical methods.

The fundamental science question behind marine cloud brightening (MCB) as a climate intervention mechanism is whether the reflectivity of marine boundary layer clouds can be deliberately increased in a controlled manner by releasing aerosols (small particles; in this case, small sea salt particles) into the marine boundary layer in targeted regions. Aerosol emissions influence cloud reflectivity through changes in the cloud droplet number concentration, which generally increases with the addition of aerosols. However, whether and how much a cloud field is brightened with the addition of aerosols depends on multiple factors, including the meteorological conditions and the concentration and size of both the injected aerosol and aerosol already present in the atmosphere. In addition, the net effect on reflectivity will depend on how the clouds respond to having higher droplet number concentrations and smaller droplet sizes. These responses may augment or offset the initial reflectivity changes in the perturbed clouds, and they may also affect the reflectivity and lifetime of clouds in adjacent areas. This project aims to conduct a series of high-resolution model runs that simulate cloud fields typical of those that would be targeted for MCB, with two goals: First, the simulations will be tested against observations to quantify how well the model reproduces unperturbed cloud fields under a range of meteorological and background aerosol conditions. Second, the model will be run to test cloud responses to the addition of small sea salt aerosol representative of what would be used for intentional marine cloud brightening, under a range of realistic meteorological and background conditions.

About half of Earth's surface is covered by clouds. Low-lying boundary layer clouds can reflect a major portion of the incoming solar radiation (about 50 W/sq-m). It has been long postulated that injection of manmade aerosols (acting as cloud condensation nuclei) can increase the droplet number concentration and thus render clouds brighter. The so-called cloud brightening would have a cooling effect on climate. Yet, the underlying physics (broadly known as aerosol-cloud interactions) is poorly represented in climate models. In this project, we aim to improve the representation of aerosol-cloud interactions in models and to use the improved models to advance our understanding of cloud brightening and its climate impacts.