Earth's Radiation Budget

We will continue to conduct regular launches (approximately every two weeks from Boulder and quarterly from Lauder, New Zealand) of 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). The measurements will be used to characterize the background state and variability of radiatively important aerosols in Earth's stratosphere. After a large 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. A program of soundings at Hilo, Hawaii (20°N), will be initiated and prospective balloon launch sites in the deep tropics, southern hemisphere sub-tropics, and high northern and southern latitudes will be identified.

The radiative balance of the upper atmosphere is dependent on water vapor, other infrared absorbing trace gases and aerosol concentrations and composition. Climate models predict that with increasing surface temperatures the primary mechanism for transporting tropospheric air into the stratosphere known as the Brewer-Dobson Circulation will strengthen, leading to changes in the stratospheric concentrations of water vapor and other greenhouse gases as well as aerosols (Solomon et al., 1986) which are all critical to understanding earth's radiative balance. We propose to enhance our capacity to track changes in stratospheric dynamics by leveraging NOAA's balloon-borne AirCore sampler to measure a suite of long-lived trace gases whose concentrations are a direct result of the exchange of air between the troposphere, stratosphere and mesosphere. The proposed work both extends the suite of AirCore compounds measured with increased vertical resolution within the stratosphere enabling a more precise analysis of the dynamical changes. The stratospheric data to be collected beginning at a quarterly frequency over Boulder, CO, considered along with a 53 year record of stratospheric ozone, a 40 year water vapor record, and a more recent record of stratospheric aerosols will provide strong constraints on models of the stratospheric circulation, will serve as a test bed for future globally distributed intensive campaigns, and will provide a foundation for a future global reference network for key stratospheric species.

For this project, CSL is working with World View Enterprises to make the first particle size distribution measurements onboard a World View Stratollite, a commercial, navigable, long-endurance stratospheric balloon platform. The Portable Optical Particle Spectrometer (POPS) instrument has been demonstrated to be a reliable and sufficiently small, lightweight instrument to enable its operation on a number of high-altitude scientific platforms, including large and small balloons and manned and unmanned aircraft. Measurements from the POPS Stratollite Mission will help us better understand stratospheric aerosol under background conditions, as well following natural injections of sulfur gases and aerosols from explosive volcanic eruptions and very large fires. POPS flights on the Stratollite will also demonstrate the potential of using new observing platforms to acquire scientific data in the stratosphere for extended periods over large geographic regions.

The Global Climate Observing System (GCOS) Reference Upper Air Network (GRUAN) was established in 2008 to be an international network of sites making reference-quality measurements of essential climate variables above Earth's surface, designed to fill an important gap in the current global observing system. GRUAN measurements are providing long-term, high-quality climate data records from the upper troposphere (UT) into the lower stratosphere (LS). These data are being used to determine trends, constrain and calibrate data from more spatially‐comprehensive observing systems (including satellites and current operational radiosonde networks), and provide important data for studying atmospheric processes. GRUAN is envisaged as a global network of 30-40 globally-dispersed sites (currently 28) that, to the extent possible, builds on existing observational networks and capabilities. This project is geared to support the three U.S. GRUAN sites in Boulder, CO; Beltsville, MD; and Lamont, OK; as well as the GRUAN station in Lauder, New Zealand. More information on GRUAN and its global distribution of sites.

Proposed solar radiation management (SRM) schemes to mitigate climate change via intentional introduction of particulate matter to the upper atmosphere may deplete the stratospheric ozone layer. Development and high-altitude deployment of a new instrument to measure trace gases that react with particulates will provide new data to better define the current sensitivity of stratospheric ozone to these processes.

2020 ERB funding was used to purchase a new time of flight chemical ionization mass spectrometer (CIMS) to investigate chemistry of gas-phase halogens and organics in the upper troposphere / lower stratosphere (UT/LS) region. Additional funding proposed here would reduce the chances of significant down-time in the field due to major equipment failure, and provides programming support to streamline the process of readying the new instrument for operation on the NASA WB-57.

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.

Nitrogen oxides (e.g. NO, NO₂, HNO₃) are key species for stratospheric chemistry, acting as radical chain propagators, or ozone destruction catalysts. We propose to build a 3-channel nitrogen oxide instrument that can be used to routinely measure mixing ratios of nitrogen oxides on stratospheric aircraft such as the NASA WB-57 or ER-2. This instrument is based on the design that has been recently demonstrated by Rollins et al. (2020) to measure nitric oxide (NO) with high sensitivity using laser-induced fluorescence (LIF). This technique is a major advance in terms of precision and operation effort over the chemiluminescent technique which has been relied on for decades. Using three channels, the new instrument would allow for routine, simultaneous measurements of nitric oxide (NO) nitrogen dioxide (NO₂) and total nitrogen oxides (i.e. NOy) during forthcoming stratospheric airborne missions to explore the effects of aerosols on stratospheric ozone chemistry.

We would like to hire an additional Single Particle Soot Photometer (SP2) operator/analyst to allow increased support of SP2 for ERB related deployments.

Many of the key optical and chemical properties of microscopic particles in the stratosphere are determined by their size and concentration. To measure these particles, they need to be carried from the ambient air into instruments within a fast-moving aircraft. Doing this requires sampling inlets that do not lose the larger particles against the walls of the inlet and downstream tubing. We propose to redevelop an existing technique, the low turbulence inlet (LTI), that has been used in the lower atmosphere to quantitatively sample the largest of these particles. By beginning development an actively controlled LTI that ingests particles and delivers them to instruments with well characterized efficiency, this project should ultimately lead to reduced uncertainties in our understanding of the radiative and chemical effects of large stratospheric particles that result from volcanic eruptions, dust storms, large wildfires, rockets, and intentionally introduced materials.

The Particle Analysis by Laser Mass Spectrometry (PALMS) instrument is a laser ionization mass spectrometer which makes in-situ measurements of the chemical composition of individual aerosol particles. Aerosols are brought into a vacuum system and individual particles are detected by light scattered as they cross the beam of a continuous laser. The scattered light signal gives a rough indication of the size of the particle and a provides a trigger for an excimer laser (193nm), which is pulsed so its beam hits the particle to desorb and ionize molecules and atoms. These ions are analyzed with a time of flight mass spectrometer to provide a complete mass spectrum from each particle. The instrument is capable of measuring particles from 0.2 to 3 microns in diameter. Analysis is complete less then 1 millisecond after the aerosols enter the inlet. Furthermore, artifacts are minimized because particles never touch a surface. The instrument can acquire either positive or negative ion spectra.

The Spectrometers for Optical Aerosol Properties (SOAP) instrument measures aerosol extinction and absorption using cavity ring-down and photoacoustic spectroscopy. It operates at one green wavelength. It is a relatively new instrument that builds on the heritage of the larger 5-channel extinction and photoacoustic instruments at the NOAA Chemical Sciences Laboratory (CSL). SOAP is relatively new, with its only mission a successful circuit on the fourth Atmospheric Tomography (ATom) deployment. SOAP makes three main contributions to aerosol science in the stratosphere. First, it measures extinction, allowing a direct comparison with SAGE and some other satellite instruments. The SOAP extinction is dried from ambient, but low relative humidity in the stratosphere means that the correction to ambient humidity is smaller than in much of the troposphere. Second, the SOAP measurements of absorption have sufficient detection limit that they would detect any unusual absorption, although not necessarily stratospheric background conditions. For example, the light absorption in a self-lofting wildfire aerosol plume (Yu et al., Science, 2019) should be directly measurable by SOAP. SOAP would measure light absorption by volcanic ash if an eruption were sampled. Third, SOAP provides an important check on integral size distribution properties. The extinction calculated from the size distribution can be compared to that measured by SOAP. The SOAP extinction measurements are extremely accurate and therefore agreement adds confidence to other integral size distribution properties such as volume or surface area.

Purchase a dedicated set of pallets to hold instrumentation on the NASA WB-57. Mounting aircraft instruments on these pallets allows for straightforward installation on the WB-57, allowing for quick deployment of the aircraft in case of rapidly evolving experiments of opportunity like a major volcanic eruption.

Operating complex scientific instruments on high-altitude aircraft such as the NASA WB-57 poses significant technical challenges due to the low-pressure and cold-temperature environment experienced in the payload bays and the need for fully autonomous operation. A critical step in ensuring science-quality measurements from airborne science missions is the field-testing of new instruments in the operational environment. This allows potential issues to be identified and addressed and instrument performance to be optimized. To ensure the flight-readiness of newly developed and modified NOAA CSL instruments in preparation for future NOAA ERBI airborne science missions, we will conduct a short, focused aircraft integration and test flight sequence on the NASA WB-57 in the fall or winter of 2021.

Atmospheric dynamics play an important role in marine cloud brightening, both in the transport of surface aerosol through the marine atmospheric boundary layer and in the activation of particles at cloud base. This project builds upon a demonstrated capability of measuring vertical profiles of wind and turbulence through the atmospheric boundary layer, both continuously for extended ship-based experiments and episodically during aircraft-based experiments. The existing airborne instrument has been operated in a downward looking mode from the NOAA Twin Otter. In order to measure vertical motion at cloud base and provide profiles through the boundary layer, the lidar needs to point both upward and downward from the aircraft. This project would add that measurement capability to the NOAA Twin Otter and also to the NOAA WP-3D – both aircraft could be involved in a potential marine cloud brightening experiment.

Scattering and absorption of solar radiation by atmospheric aerosol particles affect Earth's radiation budget, including cooling at the Earth's surface [Intergovernmental Panel on Climate Change (IPCC), 2014]. In addition, aerosol particles take up water and form cloud droplets which can increase cloud brightness and lead to a cooling of the Earth's surface. The degree to which aerosol direct forcing and interactions between aerosols and clouds are cooling the planet and offsetting warming by greenhouse gases is highly uncertain. According to the IPCC, climate forcing associated with aerosol-cloud interactions contributes the largest uncertainty to total radiative forcing estimates. Vertical profiles of aerosol and cloud properties are required to improve models and decrease uncertainties, particularly over oceans due to the susceptibility of marine clouds to small changes in aerosol concentrations (Rosenfeld et al., 2019). We propose here to perform Uncrewed Aerial System (UAS) test flights for the measurement of vertical profiles of aerosol and cloud properties in the marine boundary layer. The overall goal is to develop an observation capability to further our understanding of the impacts of aerosol on direct radiative forcing and cloud properties in the marine boundary layer, a primary objective of the NOAA Earth's Radiation Budget (ERB) Initiative. Marine stratus clouds along the western coast of the U.S. will be targeted in the June to September time frame when low level cloud cover is at a maximum (Iacobellis and Cayan, 2013). These test flights will lead to an observation system capable of operating from ships and coastal regions, with an endurance of up to 3 hours (~105 NM), and a height ceiling of 3 km.

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. Climate models also require an accurate description of the chemical processes in the stratosphere that impact the formation and loss of H₂SO₄ (sulfuric acid) and subsequent aerosol formation. A second component of our research includes a critical evaluation of the gas-phase chemical loss processes of H₂SO₄, which may impact the formation of stratospheric sulfate aerosol. The chemical reactions to be evaluated are not included in current climate-chemistry coupled modeling and will be studied using theoretical methods.

Direct observations of the outcomes from a stratospheric sulfur injection are limited to periodic volcanic eruptions. Understanding the chemical and microphysical evolution of the atmosphere following those eruptions is key for understanding the climate response to volcanic eruptions and potential stratospheric solar radiation management schemes. Here we propose to use detailed chemical and aerosol microphysical observations from the NASA DC-8 aircraft during the NASA/NOAA FIREX-AQ experiment to greatly constrain stratospheric sulfur chemistry and microphysics. We will use those observations to precisely determine the SO₂ → sulfate oxidation chemistry, and the resulting aerosol size distributions and optical properties. These will be used to evaluate the capabilities of state-of-the-art global models in predicting the resulting climate impact of stratospheric sulfur injections.

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 three 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 caused by increases in soot loading emitted by kerosene burning engines (as used by the SpaceX Falcon 9). 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.

Material injected into the upper atmosphere can be transported long distances and form complex, stratified structures. Turbulent mixing is relatively small above the planetary boundary layer and thus a plume is mainly mixed by the chaotic stretching and folding of the flow field. If a geo-engineering strategy that relies on injecting material into the upper atmosphere were to be performed, then probabilistic long-range forecasting of the transport and dispersion of the material would be needed to adequately plan releases. Short range (3-24 hour) forecasts of volcanic emissions are regularly performed for aviation, and probabilistic forecasts are in development. We propose to extend this work to longer forecasting times. Ensemble forecasts for volcanic emissions including SO₂ will be produced using the HYSPLIT transport and dispersion model driven by NOAA's global ensemble forecast system (GEFS) and evaluated with satellite observations to understand how well flow patterns and spatial coverage of material injected for geoengineering purposes can be predicted. Project outcomes will include demonstrations of typical cases, recommendations for optimal model configuration settings, and quantitative information about uncertainties that can help prioritize further work.

A major model development activity in FY20 is to implement a prognostic scheme of stratospheric aerosols in GFDL's ESM4 for tracking their concentrations, microphysical processes, radiative properties and long-range transport after injection. We propose to build upon this work to implement a unified stratospheric and tropospheric modal aerosol microphysical module to explicitly consider the key microphysical processes – including aerosol formation, growth and removal – that determine the size distributions and mixing states of different aerosols species. The additional information will be used for computing the radiative properties of aerosols and droplet activation. We propose to perform sensitivity tests to explore process-based uncertainties in the distribution and evolution of aerosols that are important for calculating their radiative effects. We also propose to introduce a treatment of aerosol-ice cloud interactions by parameterizing the effects of dust and black carbon, two major ice nuclei, on the ice crystal number concentration. This work is enabled by a newly implemented double-moment cloud microphysics scheme and a newly developed parameterization for ice nucleation in the GFDL models. The modal aerosol microphysics will be coupled to this new cloud microphysics capability.

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. This project will further include analysis of the atmospheric aerosol composition, evolution, chemistry and climate feedbacks based in multi-model comparisons, for historical and future simulations, as part of the Chemistry-Climate Modeling Initiative (CCMI). These analyses are in particular important for the upcoming WMO 2022 ozone assessment.

ERB perturbations, natural and anthropogenic alike, are an important source of predictability at timescales ranging from seasonal-to-subseasonal (S2S) to decadal. We plan to take advantage of the latest GFDL climate prediction system SPEAR, which is based on AM4/CM4, to assess how fast a robust signal on TOA radiative fluxes, surface temperature and precipitation from ERB perturbations can be detected on the regional scale. This work could be particularly relevant to the planning and monitoring of real-world deployments.

Marine Cloud Brightening (MCB) is a form of solar climate intervention that targets shallow, liquid marine clouds in the lowest 1500 m of the Earth's atmosphere. The basic notion is that an injection of particles into these 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. The goal of this project is to ascertain the spatial extent and frequency of occurrence of clouds that are most susceptible to these injections. It will also tie these susceptible clouds to the meteorological conditions that generate them. The project will also continue to pursue a range of modeling tools to strengthen our understanding of optimal seeding conditions.

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.

Earth's average temperature is set by the balance between the light absorbed and emitted by the atmosphere, ocean, and land. Sunlight also drives some of the chemical reactions in the atmosphere and so helps set the lifetime of certain trace gases. This project will increase understanding of the relationships between atmospheric conditions and the capacity of the atmosphere to remove air pollutants including both reactive greenhouse gases such as methane and some of the substances that deplete the stratospheric ozone layer. We will focus our attention over the wide swaths of ocean covered by low clouds where atmospheric conditions, including the amount of reflected sunlight, affect methane lifetime by altering its chemical sink. We will develop specialized modeling tools that tease apart the changes in the individual factors controlling the chemical sink of methane, including sunlight, temperature, and water vapor, with an emphasis on the responses to persistent changes in reflectivity.

This project will include and evaluate aerosol impacts on shallow and warm rain congestus cloud parameterization fractional cloud cover as well as coupling of the subgrid-scale clouds with radiation by generalizing the exponential-random cloud-overlap assumption used within the radiation scheme. Results and evaluations from global model simulations will be compared to observations during field experiments as well as Large Eddy Simulations (LES).

To assess the model skill both at the process level and at the phenomenal level, we propose to make extensive use of space-based and in-situ observations to constrain the model. For instance, supported by the FY20 ERB funding, Ming et al. (2020) used GFDL's AM4, nudged with re-analysis data, and NASA CERES-measured top-of-the-atmosphere (TOA) radiative fluxes to study the influence of the pandemic-related aerosol emission reductions. Specifically, we will evaluate the ability of hindcast simulations to capture observed stratospheric and tropospheric aerosol and source gas loadings and aerosol optical properties, both for volcanically quiescent as well as active periods. In-situ measurements of SO₂ conducted by NOAA CSL (Rollins et al., 2017) suggest a negligible role for tropospheric SO₂ flux in maintaining background stratospheric aerosols. We will test our model against these benchmark measurements to evaluate its capability to accurately simulate the chemistry and dynamics in the lower stratosphere. The SO₂ degassing of the Kilauea volcano on the Big Island of Hawaii was shown to increase aerosol optical depth and cloud optical depth and decrease droplet effective radius as far as 6000 km downwind over the trade cumulus region (Yuan et al., 2011). We propose to design a series of AM4 simulations to capture the observed characteristics of the degassing plume and cumulus clouds under its influence. The results would yield important insights into the model performance in representing cloud brightening.

It has been argued (Latham 1990, Latham et al. 2008) that enhancement of planetary albedo by seeding maritime boundary layer clouds may be an effective climate intervention strategy. In this approach, aerosol particles of a size distribution optimally designed to be effective cloud condensation nuclei are injected within the boundary layer to enhance the cloud drop number concentration of maritime stratocumulus. This results in two effects: 1) the cloud drops become smaller and thus the clouds are more reflective of incoming solar radiation (Twomey 1977), and 2) the clouds become more persistent and occupy a broader areal extent (Albright 1989) since this may reduce precipitation. Both effects serve to reduce the amount of solar radiation reaching the Earth's surface and therefore have a cooling effect to the planet. In this study, we propose to perform two sets of simulations using two different configurations of CESM2, in its default setting and with the newly built machine-learning emulator for warm cloud processes. In the first set of simulations, we will constrain the cloud drop number concentration within the seeding regions to investigate the effect of MCB on global climate. In the second set of simulations, we will simulate aerosol-cloud interaction by injecting sea salt particles within the seeding regions and allow the model to evolve freely to determine how the cloud drop number concentration will be altered. The outcome of this study will be a more realistic evaluation of impacts of MCB on global climate.