Department of Atmospheric Sciences Faculty Research

Permanent URI for this collectionhttps://digital.lib.washington.edu/handle/1773/36290

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Data to accompany the article "Can Observation Targeting Be a Wild Goose Chase? An Adjoint-Sensitivity Study of the 15 November 2018 Forecast Bust"
(2024-01-19) Lloveras, Daniel J.; Durran, Dale R.; Doyle, James D.
Data to accompany "The spatial heterogeneity of cloud phase observed by satellite"
(2023-08-03) Sokol, Adam B.; Storelvmo, Trude
We conduct a global assessment of the spatial heterogeneity of cloud phase within the temperature range where liquid and ice can coexist. Single-shot CALIOP lidar retrievals are used to examine cloud phase at scales as fine as 333 m, and heterogeneity is quantified according to the frequency of switches between liquid and ice along the satellite's path. In the global mean, heterogeneity is greatest between -15 and -4 °C with a peak at -5 °C, when small patches of ice are prevalent within liquid-dominated clouds. Heterogeneity ``hot spots" are typically found over the extratropical continents, whereas phase is relatively homogeneous over the Southern Ocean and the eastern subtropical ocean basins, where supercooled liquid clouds dominate. Even at a fixed temperature, heterogeneity undergoes a pronounced annual cycle that, in most places, consists of a minimum during autumn or winter and a maximum during spring or summer. Based on this spatial and temporal variability, it is hypothesized that heterogeneity is affected by the availability of ice nucleating particles. These results can be used to improve the representation of subgrid-scale heterogeneity in general circulation models, which has the potential to reduce longstanding model biases in cloud phase partitioning and radiative fluxes.
Mt. Bachelor Observatory final atmospheric data for YEAR 2022
(2023-07-14)
Mt. Bachelor Observatory final atmospheric data for YEAR 2022
Mt. Bachelor Observatory data for 2021
(2022-07-14)
Mt. Bachelor Observatory final atmospheric data for YEAR 2021
Supporting Dataset for the article by Confer et al. "Impact of changing Arctic sea ice extent, sea ice age, and snow depth on sea salt aerosol from blowing snow and the open ocean for 1980-2017"
(Journal of Geophysical Research, 2022) Confer, Kaitlyn L.; Jaeglé, L.; Liston, G. E.; Sharma, S.; Nandan, V.; Yackel, J.; Ewert, M.; Horowitz, H. M.
We evaluate the effects of rapidly changing Arctic sea ice conditions on sea salt aerosols (SSA) produced by oceanic wave-breaking and the sublimation of wind-lofted salty blowing snow on sea ice. We use the GEOS-Chem chemical transport model to assess the influence of changing extent of the open ocean, multi-year sea ice (MYI), first-year sea ice (FYI), and snow depths on SSA emissions for 1980-2017. We combine snow depths from the Lagrangian snow-evolution model (SnowModel-LG) together with an empirically-derived snow salinity function of snow depth to derive spatially and temporally varying snow surface salinity over Arctic FYI. We find that pan-Arctic SSA surface mass concentrations have increased by 6-12% decade-1 during the cold season (November – April) and by 7-11% decade-1 during the warm season (May – October). The cold season trend is due to increasing blowing snow SSA originating from FYI: as MYI is replaced by FYI with thinning snow depths, snow surface salinity increases by more than 11% decade-1. During the warm season, rapid sea ice loss and thus increasing open ocean SSA are the cause of modeled SSA trends. Observations of SSA mass concentrations at Alert, Canada display positive trends during the cold season (10-12% decade-1), consistent with our pan-Arctic simulations. During fall, Alert observations show a negative trend (-18% decade-1), due to locally decreasing wind speeds and thus lower open ocean emissions. These significant changes in SSA concentrations could potentially affect past and future bromine explosions and Arctic climate feedbacks.
Beautiful Days in the Neighborhood: Land-Atmosphere Interactions as Drivers of Forest Expansion
(2022-11-14) Shum, Greta; Laguë, Marysa; Rushley, Stephanie; Swann, Abigail
At the end of glacial periods, warmer temperatures induce ice sheet retreat, exposing the land surface for forest establishment. Forest emergence decreases land surface albedo, leading to additional local warming, and modifies the exchange of water and energy between the land and atmosphere. These responses induce changes in the local atmosphere that have the potential to drive plant-atmosphere warming feedbacks and forest expansion beyond what is orbitally driven. Pollen records show rapid expansion of needleleaf evergreen forest in Alaska following North American deglaciation around 6,000 years ago. Using this period as a case study, we explore the possible role of plant-atmosphere feedbacks in accelerating forest expansion using a simplified reconstruction of this period. We simulate the climate response to initial forest establishment and then apply the climate modified by the forest to nearby vegetation to determine if initial forest expansion leads to more favorable growing conditions in the region. We find that the existence of the forest produces favorable conditions during the growing season nearby that would promote forest expansion. The forest acts as a source of heat and moisture for plants west of the forest, leading them to experience earlier springtime temperatures and snowmelt, and further growth. Summertime cooling and cloud formation over the forest also drives a circulation change that reduces summertime cloud cover south of the forest, increasing solar radiation reaching the plants, and driving warming. By isolating these vegetation-atmosphere interactions as the mechanism of increased growth, we demonstrate the potential for forest expansion to be accelerated in a way that has not been highlighted before. Our results can be used to improve our interpretation of biophysical impacts from climate change, afforestation projects, in addition to known past forest establishment. By examining these feedbacks, we seek to gain a more comprehensive understanding of past and potential land- atmosphere interactions.
Data to accompany the article "The Predictability of Midlatitude Cyclones: Don't Sweat the Small Stuff"
(2022-11-04) Lloveras, Daniel
We use convection-permitting idealized simulations of moist midlatitude cyclones to compare the growth of synoptic-scale initial perturbations derived from an adjoint model with the growth of monochromatic-wavelength perturbations at the smallest resolved scale. When the initial-error magnitudes are comparable to those from present-day data assimilation systems, the adjoint-derived perturbations significantly change the intensity and location of the cyclone by projecting onto the synoptic-scale baroclinically unstable growth. In contrast, the wave-like perturbations grow with the moist convection, but the errors remain on the mesoscale and localized to the precipitating regions through lead times of up to 4~days, causing only negligible changes to the midlatitude-cyclone forecast. The adjoint-derived perturbations produce the most significant changes despite the fact that the adjoint model is run at a much coarser resolution to satisfy the tangent-linear approximation, and as such has the potential to miss nonlinear contributions to error growth from moist convection. When the initial-error magnitudes are reduced by factors of 10 and 100, the adjoint-derived and wave-like perturbations both grow rapidly with the moist convection, but this growth does not significantly alter the cyclone's development. Using quasigeostrophic potential vorticity inversion, we investigate the balanced response produced by the perturbations after 4~days of growth. Only the full-magnitude adjoint-derived perturbations lead to balanced growth with the synoptic-scale baroclinic instability; the balanced error signatures in the other experiments remain on the mesoscale and localized to the convection, in contrast to a widely cited conceptual model for error growth. These results suggest that synoptic-scale initial errors that project strongly onto regions of high adjoint sensitivity are more important for 2--4-day practical midlatitude-cyclone forecasts than arbitrarily small-scale initial errors that grow with the moist convection.
The Antarctic Ozone Hole and the pattern effect on climate sensitivity
(2022-07-29) Hartmann, Dennis L
Since about 1980 the tropical Pacific has been anomalously cold while the broader tropics have warmed. This has caused anomalous weather in mid-latitudes as well as a reduction in the apparent sensitivity of the climate associated with enhanced low cloud abundance over the cooler waters of the eastern tropical Pacific. Recent modeling work has shown that cooler temperatures over the Southern Ocean around Antarctica can lead to cooler temperatures over eastern tropical Pacific. Here we suggest that surface wind anomalies associated with the Antarctic Ozone Hole can cause cooler temperatures over the Southern Ocean that extend into the Tropics. We use the short-term variability of the Southern Annular Mode of zonal wind variability to show an association between surface zonal wind variations over the Southern Ocean, cooling over the Southern Ocean, and cooling in the eastern tropical Pacific. This suggests that the cooling of the eastern tropical Pacific may be associated with the onset of the Antarctic Ozone Hole
Dataset supporting "Mesoscale Convective Clustering Enhances Tropical Precipitation"
(2022-06-15) Angulo-Umana, Pedro
In the tropics, extreme precipitation events are often caused by mesoscale systems of organized, spatially clustered deep cumulonimbi, posing a substantial risk to life and property. While the clustering of convective clouds has been thought to strengthen precipitation rate, no quantitative estimates of this hypothesized enhancement exist. In this study, after isolating the effects of mesoscale convective clustering on precipitation, we find that strongly clustered oceanic convection precipitates about 50% more intensely than weakly clustered convection. We further show that this enhancement is primarily attributable to an increase in convective precipitation rate when the environment is less than 70% saturated, with increases in the size of the rainy stratiform region being of equal or greater importance when the environment is closer to saturation. Our results suggest that a correct representation of mesoscale organized convective systems in numerical weather and climate models is needed for accurate predictions of extreme precipitation events.
Mt. Bachelor Observatory data for 2020
(2022-05-18) Jaffe, Daniel A.
Mt. Bachelor Observatory final atmospheric data (v1) for Year 2020.
Supporting Data for Sokol & Hartmann (2022), "Convective aggregation, static stability, and the congestus mode in cloud-resolving simulations of radiative-convective equilibrium"
(2022) Sokol, Adam B; Hartmann, Dennis L; Sokol, Adam
This study examines how the congestus mode of tropical convection is expressed in numerical simulations of radiative-convective equilibrium (RCE). We draw insights from the ensemble of cloud-resolving models participating in the RCE Model Intercomparison Project (RCEMIP) and from a new ensemble of two-dimensional RCE simulations. About half of the RCEMIP models produce a congestus circulation that is distinct from the deep and shallow circulation modes. In both ensembles, congestus strength is associated with large-scale convective aggregation. Aggregation dries out the upper troposphere, which allows moist congestus outflow to undergo strong radiative cooling. The cooling generates divergence that promotes continued congestus overturning (a positive feedback). This mechanism is fundamentally similar to the driving of shallow circulations by radiative cooling at the top of the surface boundary layer. Aggregation and congestus invigoration are also associated with enhanced static stability throughout the troposphere. Changes in entrainment cooling are found to play an important role in stability enhancement, as has been suggested previously. A modeling experiment shows that enhanced stability is not necessary for congestus invigoration; rather, invigoration itself contributes to midlevel stability enhancement via its impact on the vertical profile of radiative cooling. When present, congestus circulations have a large impact on the mean RCE atmospheric state; for this reason, their inconsistent representation in models and their impact on the real tropical atmosphere warrant further scrutiny.
Mt. Bachelor Observatory data for 2019
(2022) Jaffe, Daniel A.
Mt. Bachelor Observatory final atmospheric data for YEAR 2019.
Data to accompany the article "Two-way teleconnections between the Southern Ocean and the tropical Pacific via a dynamic feedback"
(2021-01-10) Dong, Yue; Armour, Kyle; Battisti, David; Blanchard-Wrigglesworth, Edward
Despite substantial global mean warming, surface cooling has occurred in both the tropical eastern Pacific and Southern Ocean over the past 40 years, influencing both regional climates and estimates of Earth’s climate sensitivity to rising greenhouse gases. Using a paleo-reconstruction dataset of the past 2000 years, we find that sea-surface temperatures (SSTs) over the tropical eastern Pacific and part of the Southern Ocean near the southeast Pacific closely co-vary with each other on decadal to multidecadal timescales. While a tropical influence on the extratropics has been extensively studied in the literature, here we demonstrate that the teleconnection works in the other direction as well, suggesting that the observed tropical eastern Pacific cooling may be connected to the observed Southern Ocean cooling. Using a slab-ocean model, we find that the tropical Pacific SST response to an imposed Southern Ocean surface heat flux forcing is sensitive to the longitudinal location of that forcing, suggesting an atmospheric pathway associated with regional dynamics rather than reflecting a zonal-mean energetic constraint. The transient response shows that an imposed Southern Ocean cooling first propagates into the tropics by mean-wind advection. Once tropical Pacific SSTs are perturbed, they then drive remote changes to the sea-level pressure and surface winds in the extratropics which further enhance both Southern Ocean and tropical cooling. These results suggest a mutually interactive teleconnection between the Southern Ocean and tropical Pacific through atmospheric circulations, and highlight potential impacts on the tropics from the extratropical climate changes over the instrumental record and in the future.
Stratosphere-troposphere exchanges of air mass and ozone concentration in the Last Glacial Maximum
(2021) Wang, Mingcheng; Fu, Qiang; Solomon, Susan; Alexander, Becky; White, Rachel H
Stratosphere-troposphere exchange (STE) of ozone represents a significant source term in the tropospheric ozone budget and can impact surface ozone concentrations, tropospheric oxidation capacity, and methane lifetime. Using the Whole Atmosphere Community Climate Model 6, changes in the air mass and ozone STEs in the Last Glacial Maximum (LGM) as compared with preindustrial (PI) climate are investigated. We deploy the dynamic isentropic surfaces that are determined by fitting to the tropical tropopauses as the upper boundary of the lowermost stratosphere in a mass budget approach, which are suitable to estimate air mass and ozone STEs and their changes in different climates. It is shown that the magnitude of ozone STE is decreased by 14-19%, 18-24%, 19-20%, 16-21%, 15-21% over the Northern hemisphere extratropics, Southern hemisphere extratropics, the tropics, the extratropics, and the globe, respectively, in the LGM versus PI. The extratropical and global decreases are mainly caused by decreased ozone in the extratropical lower stratosphere associated with a weakening of Brewer-Dobson circulation, while changes in air mass fluxes play a minor role because the effects of weakening Brewer-Dobson circulation and increased isentropic density partly cancel each other. Analysis of the modelled tropospheric ozone budget indicates that the ozone STE in the LGM is 28% of the tropospheric ozone production rate, as compared to about 9% in the modern climate (year 2000) and 19% in the PI.
Data supporting "Biased estimates of Equilibrium Climate Sensitivity and Transient Climate Response derived from historical CMIP6 simulations"
(2021-11-29) Dong, Yue
This study assesses the effective climate sensitivity (EffCS) and transient climate response (TCR) derived from global energy budget constraints within historical simulations of 8 CMIP6 global climate models (GCMs). These calculations are enabled by use of the Radiative Forcing Model Intercomparison Project (RFMIP) simulations, which permit accurate quantification of the radiative forcing. Long-term historical energy budget constraints generally underestimate EffCS from CO2 quadrupling and TCR from CO2 ramping, owing to changes in radiative feedbacks and changes in ocean heat uptake efficiency. Atmospheric GCMs forced by observed warming patterns produce lower values of EffCS that are more in line with those inferred from observed historical energy budget constraints. The discrepancies in the EffCS estimates from historical energy budget constraints of models and observations are traced to discrepancies between modeled and observed historical surface warming patterns.
The Vertical Profile of Radiative Cooling and Lapse Rate in a Warming Climate
(2021-10-28) Hartmann, Dennis L
The vertical profile of clear-sky radiative cooling places important constraints on the vertical structure of convection and associated clouds. Simple theory using the cooling-to-space approximation is presented to indicate that the cooling rate in the upper troposphere should increase with surface temperature. The theory predicts how the cooling rate depends on lapse rate in an atmosphere where relative humidity remains approximately a fixed function of temperature. This theory is tested with one-dimensional radiative transfer calculations and radiative-convective equilibrium simulations. For climate simulations that produce an approximately moist adiabatic lapse rate, the radiative cooling profile in K/day becomes increasingly top-heavy with increasing surface temperature. If however the temperature profile warms more slowly than a moist adiabatic profile in mid-troposphere then the cooling rate in the upper and lower troposphere increase at more similar rates as the climate warms, with important implications for convection, clouds and associated deep and shallow circulations.
Data to support "Anthropogenic Impacts on Tropospheric Reactive Chlorine since the Preindustrial"
(2021-06-24) Zhai, Shuting
Tropospheric reactive gaseous chlorine (Cly) impacts the atmosphere’s oxidation capacity with implications for chemically reduced gases such as methane. Here we use Greenland ice-core records of chlorine, sodium, and acidity, and global model simulations to show how tropospheric Cly has been impacted by anthropogenic emissions since the 1940s. We show that anthropogenic contribution of non-sea-salt chlorine significantly influenced total chlorine and its trends after the 1940s. The modeled regional 170% Cly increase from preindustrial to the 1970s was driven by acid displacement from sea-salt-aerosol, direct emission of hydrochloric acid (HCl) from combustion, and chemical reactions driven by anthropogenic nitrogen oxide (NOx) emissions. Since the 1970s, the modeled 6% Cly decrease was caused mainly by reduced anthropogenic HCl emissions from air pollution mitigation policies. Our findings suggest that anthropogenic emissions of acidic gases and their emission control strategies have substantial impacts on Cly with implications for tropospheric oxidants, methane, and mercury.
Data to accompany the article "Radiative Cooling, Latent Heating, and Cloud Ice in the Tropical Upper Troposphere"
(2021-05-27) Sokol, Adam B.
The radiative cooling rate in the tropical upper troposphere is expected to increase as climate warms. Since the tropics are approximately in radiative-convective equilibrium (RCE), this implies an increase in the convective/latent heating. We examine the impact of these changes on the vertical profile of cloud ice amount in RCE simulations using a cloud-resolving model. Three simulations are conducted: a control run, a warming run, and an experimental run in which there is no warming but the cooling rate is artificially adjusted to mimic a warming scenario. We find that the efficiency of latent heating by cloud ice increases with warming, which tempers the response of the mean cloud ice profile. An analytic expression relating the ice-related latent heating rate to a number of other factors is derived and used to understand the model results. This reveals that the increase in latent heating efficiency with warming is driven mostly by 1) the migration of isotherms to lower pressure and 2) a slight warming of the top of the convecting layer. These physically robust mechanisms curtail the response of the cloud ice profile to global warming.
Data to accompany the article "Atmospheric Predictability Is Not Sensitive to the Slope of the Background Kinetic Energy Spectrum"
(2021-05-23) Lloveras, Daniel
We investigate the sensitivity of atmospheric predictability to the slope of the background kinetic energy spectrum E by adding initial errors to simulations of idealized moist mid-latitude cyclones at several wavenumbers k for which the slope of E(k) is significantly different. These different slopes arise from 1) differences in the E(k) generated by cyclones growing in two different moist baroclinically unstable environments, and 2) differences in the horizontal scale at which initial perturbations are added, with E(k) having steeper slopes at larger scales. When small-amplitude potential temperature perturbations are added, the error growth through the subsequent 36-hour simulation is not sensitive to the slope of E(k) nor to the horizontal scale of the initial error. In all cases with small-amplitude perturbations, the error growth in physical space is dominated by moist convection along frontal boundaries. As such, the error field is localized in physical space and broad in wavenumber (spectral) space. In moist mid-latitude cyclones, these broadly distributed errors in wavenumber space grow up-amplitude rather than through an upscale cascade to progressively longer wavelengths. In contrast, the error distribution in homogeneous turbulence is broad in physical space and localized in wavenumber space, and dimensional analysis can be used to estimate the error growth rate at a specific wavenumber k from E(k). Predictability estimates derived in this manner, and from the numerical solutions of idealized models of homogeneous turbulence, depend on whether the slope of E(k) is shallower or steeper than k^{-3}, which differs from the slope-insensitive behavior exhibited by moist mid-latitude cyclones.
Supporting data for Chan et al. (2021) "Heterogeneous nitrate production mechanisms in intense haze events in the North China Plain"
(2021-04-21) Chan, Yuk Chun
This dataset includes observational and modeling data in support of the findings in Chan, Y.C., M.J. Evans, P. He, C.D. Holmes, L. Jaegle, P. Kasibhatla, X.-Y. Liu, T. Sherwen, J.A. Thornton, X. Wang, Z. Xie, S. Zhai, and B. Alexander "Heterogeneous nitrate production mechanisms in intense haze events in North China" which was published in the Journal of Geophysical Research: Atmospheres in 2021. Scripts for reproducing the published figures and instructions for reproducing model experiments are also included. More details can be found in the data-and-analysis-script.readme. Professor Becky Alexander (beckya@uw.edu) is the corresponding author.

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