In the near future, there will be several new instruments measuring atmospheric composition from geostationary orbit over North America, East Asia, and Europe. This constellation of satellites will ...provide high resolution, time resolved measurements of trace gases and aerosols for monitoring air quality and tracking pollution sources. This paper describes a detailed, fast, and accurate (less than 1.0% uncertainty) method for calculating synthetic top of the atmosphere (TOA) radiances from a global simulation with a mesoscale free running model, the GEOS-5 Nature Run, for remote sensing instruments in geostationary orbit that measure in the ultraviolet-visible spectral range (UV-Vis). Generating these synthetic observations is the first step of an Observing System Simulation Experiment (OSSE), a framework for evaluating the impact of a new observation or algorithm. This paper provides details of the model sampling, aerosol and cloud optical properties, surface reflectance modeling, Rayleigh scattering calculations, and a discussion of the uncertainties of the simulated TOA radiance. An application for the simulated TOA radiance observations is demonstrated in the manuscript. Simulated TEMPO (Tropospheric Emissions: Monitoring of Pollution) and GOES-R (Geostationary Operational Environmental Satellites) observations were used to show how observations from the two instruments could be combined to facilitate aerosol type discrimination. The results demonstrate the viability of a detailed instrument simulator for radiance measurements in the UV-Vis that is capable of accurately simulating high resolution, time-resolved measurements with reasonable computational efficiency.
The development of and results obtained with a variable-resolution stretched-grid GCM for the regional climate simulation mode are presented. A global variable-resolution stretched grid used in the ...study has enhanced horizontal resolution over the United States as the area of interest. The stretched-grid approach is an ideal tool for representing regional- to global-scale interactions. It is an alternative to the widely used nested-grid approach introduced over a decade ago as a pioneering step in regional climate modeling. The major results of the study are presented for the successful stretched-grid GCM simulation of the anomalous climate event of the 1988 U.S. summer drought. The straightforward (with no updates) 2-month simulation is performed with 60-km regional resolution. The major drought fields, patterns, and characteristics, such as the time-averaged 500-hPa heights, precipitation, and the low-level jet over the drought area, appear to be close to the verifying analyses for the stretched-grid simulation. In other words, the stretched-grid GCM provides an efficient downscaling over the area of interest with enhanced horizontal resolution, in spite of degradation of skill over the coarser resolution far away from the area of interest. It is also shown that the stretched-grid GCM skill is sustained over the area of interest throughout the simulation extended to 1 yr. The stretched-grid GCM, developed and tested in a simulation mode, is a viable tool for regional and subregional climate studies and applications.
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DOBA, IZUM, KILJ, NUK, PILJ, PNG, SAZU, UILJ, UKNU, UL, UM, UPUK
Abstract
Multiyear (1987–97) limited ensemble integrations using a stretched-grid GCM, previously developed and experimented with by the authors, are employed for U.S. regional climate simulations. ...The ensemble members (six in total) are produced at two different regional resolutions: three members with 60-km and the other three members with 10-km regional resolution. The use of these two finer and coarser regional resolution ensemble members allows one to examine the impact of resolution on the overall quality of the simulated regional fields. For the multiyear ensemble simulations, an efficient regional downscaling to realistic mesoscales has been obtained. The ensemble means of the midtroposphere prognostic variables (height and meridional wind) show an overall good resemblance to the global reanalysis, especially for summer. Low-level features like the warm season Great Plains low-level jet are well represented in the simulations. During winter the 100-km simulations develop a southward wind east of the Rockies that is present neither in the reanalyses nor in the 60-km simulations. The analysis of the annual mean precipitation and its variance reveals that the ensemble simulations reproduce many of the observed features of a high-resolution rain gauge dataset analyzed on a 0.5° × 0.5° grid. Signal-to-noise ratios are larger than 1.5 s over a major part of the United States, especially over the Midwest and also over the mountainous regions like the Rockies and the Appalachians, suggesting that the orographic forcing is contributing to a larger signal. The ratios are smaller toward the eastern and western U.S. coastlines. This result could be attributed, at least in part, to limits in the representation of the land–sea contrasts.
For comparison purposes, an additional simulation has been performed using a global uniform 2° × 2.5° grid with the same number of global grid points as those of the above stretched grids. The stretched-grid GCM ensemble means show, overall, a better regional depiction of features than those of the uniform-grid GCM.
The results of the study show that even using limited ensemble integrations with a state-of-the-art stretched-grid GCM is beneficial for reducing the uncertainty of the multiyear regional climate simulation, especially when using finer 60-km regional resolution.
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The new stretched‐grid (SG) design with multiple (four) areas of interest, one at each global quadrant, is implemented into both a SG general circulation model (GCM) and a SG data assimilation system ...(DAS). The four areas of interest include the United States/northern Mexico, the El Niño area/central South America, India/China, and the eastern Indian Ocean/Australia. Both SG‐GCM and SG‐DAS annual (November 1997 to December 1998) integrations are performed with 50‐km regional resolution. The efficient regional downscaling to mesoscales is obtained for each of the four areas of interest, while the consistent interactions between regional and global scales and the high quality of global circulation are preserved. This is the advantage of the SG approach. The global variable‐resolution DAS incorporating the SG‐GCM has been developed and tested as an efficient tool for producing regional analyses and diagnostics with enhanced mesoscale resolution. The anomalous regional climate events of 1998 that occurred over the United States, Mexico, South America, China, India, African Sahel, and Australia are investigated in both simulation and data assimilation modes. The assimilated products are also used, along with gauge precipitation data, for validating the simulation results. The obtained results show that the SG‐GCM and SG‐DAS are capable of producing realistic high‐quality simulated and assimilated products at mesoscale resolution for regional climate studies and applications.
First we verify whether dynamical core integrations with both uniform and stretched grids can or probably should be routinely performed in many cases with orographic forcing included as an integral ...part of model dynamics. ...we check whether using a variable resolution dynamical core with a realistic orographic forcing gives a significant downscaling over the area of interest (and its vicinity).
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North African dust reaches the southeastern United States every summer. Size-resolved dust mass measurements taken in Miami, Florida, indicate that more than one-half of the surface dust mass ...concentrations reside in particles with geometric diameters less than 2.1 µm, while vertical profiles of micropulse lidar depolarization ratios show dust reaching above 4 km during pronounced events. These observations are compared to the representation of dust in the Modern-Era Retrospective analysis for Research and Applications, version 2 (MERRA-2) aerosol reanalysis and closely related Goddard Earth Observing System model version 5 (GEOS-5) Forward Processing (FP) aerosol product, both of which assimilate satellite-derived aerosol optical depths using a similar protocol and inputs. These capture the day-to-day variability in aerosol optical depth well, in a comparison to an independent sun-photometer-derived aerosol optical depth dataset. Most of the modeled dust mass resides in diameters between 2 and 6 µm, in contrast to the measurements. Model-specified mass extinction efficiencies equate light extinction with approximately 3 times as much aerosol mass, in this size range, compared to the measured dust sizes. GEOS-5 FP surface-layer sea salt mass concentrations greatly exceed observed values, despite realistic winds and relative humidities. In combination, these observations help explain why, despite realistic total aerosol optical depths, (1) free-tropospheric model volume extinction coefficients are lower than those retrieved from the micro-pulse lidar, suggesting too-low model dust loadings in the free troposphere, and (2) model dust mass concentrations near the surface can be higher than those measured. The modeled vertical distribution of dust, when captured, is reasonable. Large, aspherical particles exceeding the modeled dust sizes are also occasionally present, but dust particles with diameters exceeding 10 µm contribute little to the measured total dust mass concentrations after such long-range transport. Remaining uncertainties warrant a further integrated assessment to confirm this study's interpretations.
Using a stratospheric-tropospheric data assimilation system, referred to as STRATAN, a minor sudden stratospheric warming that occurred in January 1989 is investigated. The event had a maximum ...influence on the stratospheric circulation near 2 hPa. The zonal mean circulation reversed briefly in the polar region as the temperature increased 34 K in 3 days. The cause of the warming is shown to be the rapid development and subsequent movement of a warm anomaly, which initially developed in the midlatitudes. The development of the warm anomaly is caused by adiabatic descent, and the dissipation by radiative cooling. A brief comparison with the NMC analysis and temperature sounding data is also presented.
Biomass burning aerosol impacts aspects of the atmosphere and Earth system through direct and semi-direct effects, as well as influencing air quality. Despite its importance, the representation of ...biomass burning aerosol is not always accurate in numerical weather prediction and climate models or reanalysis products. Using observations collected as part of the Cloud, Aerosol and Monsoon Processes Philippines Experiment (CAMP2Ex) in August through October of 2019, aerosol concentration and optical properties are evaluated within the Goddard Earth Observing System (GEOS) and its underlying aerosol module, GOCART. In the operational configuration, GEOS assimilates aerosol optical depth observations at 550 nm from AERONET and MODIS to constrain aerosol fields. Particularly for biomass burning aerosol, without the assimilation of aerosol optical depth, aerosol extinction is underestimated compared to observations collected in the Philippines region during the CAMP2Ex campaign. The assimilation process adds excessive amounts of carbon to account for the underestimated extinction, resulting in positive biases in the mass of black and organic carbon, especially within the boundary layer, relative to in situ observations from the Langley Aerosol Research Group Experiment. Counteracting this, GEOS is deficient in sulfate and nitrate aerosol just above the boundary layer. Aerosol extinction within GEOS is a function of the mass of different aerosol species, the ambient relative humidity, the assumed spectral optical properties, and particle size distribution per species. The relationship between dry and ambient extinction in GEOS reveals that hygroscopic growth is too high within the model for biomass burning aerosol. An additional concern lies in the assumed particle size distribution for GEOS, which has a single mode radius that is too small for organic carbon. Variability in the observed particle size distribution for biomass burning aerosol within a single flight also illuminates the fact that a single assumed particle size distribution is not sufficient and that for a proper representation, a more advanced aerosol module within GEOS may be necessary.
The southeastern Atlantic is home to an expansive smoke aerosol plume overlying a large cloud deck for approximately a third of the year. The aerosol plume is mainly attributed to the extensive ...biomass burning activities that occur in southern Africa. Current Earth system models (ESMs) reveal significant differences in their estimates of regional aerosol radiative effects over this region. Such large differences partially stem from uncertainties in the vertical distribution of aerosols in the troposphere. These uncertainties translate into different aerosol optical depths (AODs) in the planetary boundary layer (PBL) and the free troposphere (FT). This study examines differences of AOD fraction in the FT and AOD differences among ESMs (WRF-CAM5, WRF-FINN, GEOS-Chem, EAM-E3SM, ALADIN, GEOS-FP, and MERRA-2) and aircraft-based measurements from the NASA ObseRvations of Aerosols above CLouds and their intEractionS (ORACLES) field campaign. Models frequently define the PBL as the well-mixed surface-based layer, but this definition misses the upper parts of decoupled PBLs, in which most low-level clouds occur. To account for the presence of decoupled boundary layers in the models, the height of maximum vertical gradient of specific humidity profiles from each model is used to define PBL heights.
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