scholarly journals Harnessing Stratospheric Diffusion Barriers for Enhanced Climate Geoengineering

2020 ◽  
Author(s):  
Nikolas O. Aksamit ◽  
Ben Kravitz ◽  
Douglas G. MacMartin ◽  
George Haller
Keyword(s):  
Climate Modeling ◽  
Feasibility Studies ◽  
Reanalysis Data ◽  
Diffusion Barriers ◽  
Sulfate Aerosol ◽  
Shortwave Radiation ◽  
Time Varying ◽  
Wind Fields ◽  
Material Transport ◽  
Transport Barriers

Abstract. Stratospheric sulfate-aerosol geoengineering is a proposed method to temporarily intervene in the climate system to increase reflectance of shortwave radiation and reduce mean global temperature. In previous climate modeling studies, choosing injection locations for geoengineering aerosols has thus far only utilized average dynamics of stratospheric wind fields instead of accounting for the essential role of time-varying material transport barriers in turbulent atmospheric flows. Here we conduct the first analysis of sulfate aerosol dispersion in the stratosphere comparing a now-standard fixed-injection scheme with time-varying injection locations that harness short-term stratospheric diffusion barriers. We show how diffusive transport barriers can quickly be identified and inform optimal injection locations using short forecast and reanalysis data. Within the first seven days of transport, the dynamics-based approach is able to produce particle distributions with greater global coverage than fixed-site methods with fewer injections. Additionally, this enhanced dispersion slows aerosol microphysical growth, increasing lifespan of sulfate aerosols at monthly and yearly timescales. We conclude that previous feasibility studies of geoengineering likely underestimate the cooling efficiency of sulfate aerosol geoengineering.

scholarly journals Harnessing stratospheric diffusion barriers for enhanced climate geoengineering

2021 ◽  
Vol 21 (11) ◽  
pp. 8845-8861
Author(s):  
Nikolas O. Aksamit ◽  
Ben Kravitz ◽  
Douglas G. MacMartin ◽  
George Haller
Keyword(s):  
Radiative Forcing ◽  
Diffusion Barriers ◽  
Sulfate Aerosol ◽  
Shortwave Radiation ◽  
Great Promise ◽  
Time Varying ◽  
Material Transport ◽  
Transport Barriers ◽  
Aerosol Dispersion

Abstract. Stratospheric sulfate aerosol geoengineering is a proposed method to temporarily intervene in the climate system to increase the reflectance of shortwave radiation and reduce mean global temperature. In previous climate modeling studies, choosing injection locations for geoengineering aerosols has, thus far, only utilized the average dynamics of stratospheric wind fields instead of accounting for the essential role of time-varying material transport barriers in turbulent atmospheric flows. Here we conduct the first analysis of sulfate aerosol dispersion in the stratosphere, comparing what is now a standard fixed-injection scheme with time-varying injection locations that harness short-term stratospheric diffusion barriers. We show how diffusive transport barriers can quickly be identified, and we provide an automated injection location selection algorithm using short forecast and reanalysis data. Within the first 7 d days of transport, the dynamics-based approach is able to produce particle distributions with greater global coverage than fixed-site methods with fewer injections. Additionally, this enhanced dispersion slows aerosol microphysical growth and can reduce the effective radii of aerosols up to 200–300 d after injection. While the long-term dynamics of aerosol dispersion are accurately predicted with transport barriers calculated from short forecasts, the long-term influence on radiative forcing is more difficult to predict and warrants deeper investigation. Statistically significant changes in radiative forcing at timescales beyond the forecasting window showed mixed results, potentially increasing or decreasing forcing after 1 year when compared to fixed injections. We conclude that future feasibility studies of geoengineering should consider the cooling benefits possible by strategically injecting sulfate aerosols at optimized time-varying locations. Our method of utilizing time-varying attracting and repelling structures shows great promise for identifying optimal dispersion locations, and radiative forcing impacts can be improved by considering additional meteorological variables.

scholarly journals A comparison of Loon balloon observations and stratospheric reanalysis products

2017 ◽  
Vol 17 (2) ◽  
pp. 855-866 ◽  
Author(s):  
Leon S. Friedrich ◽  
Adrian J. McDonald ◽  
Gregory E. Bodeker ◽  
Kathy E. Cooper ◽  
Jared Lewis ◽  
...  
Keyword(s):  
Reanalysis Data ◽  
Location Information ◽  
Data Sets ◽  
Wind Fields ◽  
Weather Forecasts ◽  
Wind Speeds ◽  
Zonal Winds ◽  
Long Duration ◽  
Environmental Prediction ◽  
Modern Era

Abstract. Location information from long-duration super-pressure balloons flying in the Southern Hemisphere lower stratosphere during 2014 as part of X Project Loon are used to assess the quality of a number of different reanalyses including National Centers for Environmental Prediction Climate Forecast System version 2 (NCEP-CFSv2), European Centre for Medium-Range Weather Forecasts (ERA-Interim), NASA Modern Era Retrospective-Analysis for Research and Applications (MERRA), and the recently released MERRA version 2. Balloon GPS location information is used to derive wind speeds which are then compared with values from the reanalyses interpolated to the balloon times and locations. All reanalysis data sets accurately describe the winds, with biases in zonal winds of less than 0.37 m s−1 and meridional biases of less than 0.08 m s−1. The standard deviation on the differences between Loon and reanalyses zonal winds is latitude-dependent, ranging between 2.5 and 3.5 m s−1, increasing equatorward. Comparisons between Loon trajectories and those calculated by applying a trajectory model to reanalysis wind fields show that MERRA-2 wind fields result in the most accurate simulated trajectories with a mean 5-day balloon–reanalysis trajectory separation of 621 km and median separation of 324 km showing significant improvements over MERRA version 1 and slightly outperforming ERA-Interim. The latitudinal structure of the trajectory statistics for all reanalyses displays marginally lower mean separations between 15 and 35° S than between 35 and 55° S, despite standard deviations in the wind differences increasing toward the equator. This is shown to be related to the distance travelled by the balloon playing a role in the separation statistics.

The teleconnection between the Siberian snow-albedo feedback and the spring East Asian dust cycle : based on Last Millennium Ensemble

2020 ◽  
Author(s):  
Heng Liu
Keyword(s):  
East Asian ◽  
Lower Troposphere ◽  
Reanalysis Data ◽  
Asian Dust ◽  
Shortwave Radiation ◽  
Last Millennium ◽  
Albedo Feedback ◽  
Snow Albedo ◽  
The Past ◽  
Westerly Winds

<p>According to the reanalysis data of recent years, the Siberian snow-albedo feedback is found to play a crucial role on the spring East Asian dust cycle by influence local energy budget and circulation. By analyzing the CESM Last Millennium Ensemble conducted by National Center for Atmospheric Research (NCAR), we found that the spring East Asian dust burden is significantly correlated with the snow-albedo over Siberia during the past millennium. The correlation coefficient between the snow depth over Siberia and the East Asian dust burden reaches to 0.56. The cloud fraction over Siberia is also correlated with the dust burden with a coefficient of 0.40. The Siberian snow cover reflects shortwave radiation and cools down the lower and middle troposphere, which leads to more clouds and snows occurring over Siberia. The increased cloud cover therefore reflects more shortwave to cool down the surface as a positive feedback. The cooling of lower troposphere over Siberia induces cyclonic wind anomalies around the region, enhances the westerly winds over the East Asian deserts which locate on the south side of Siberia and finally promotes the East Asian dust cycle.</p>

How well do ERA5/WRF generated wind fields reflect the seasonal variability of the spatio-temporal characteristics of wind field, tested for North-Atlantic conditions

2021 ◽  
Author(s):  
Hans Georg Beyer ◽  
Tourid Poulsen
Keyword(s):  
Spectral Characteristics ◽  
Reanalysis Data ◽  
Spatial Inhomogeneity ◽  
Spectral Structure ◽  
Wind Fields ◽  
Temporal Characteristics ◽  
Wind Speeds ◽  
Weather Model ◽  
Spatially Distributed ◽  
Spatio Temporal

<p>Spatial and temporal characteristics of simulated wind fields - stemming from the high-resolution weather model WRF with boundary conditions from ERA5 reanalysis data had been validated against the respective data stemming from measurements regarding annual characteristics as reported by [1]. As one result, the tendency of the WRF sets showed some overestimation of the coherency and underestimation of the power spectral density (PSD).</p><p>Here, this investigation is deepened to look on the capability of the modelled data to reflect the variability of the PSD and coherencies of the wind speed fluctuations on a monthly and seasonal (three- monthly) scale.</p><p>The intra annual variation of the PSD and the coherence functions are well captured by the WRF-generated wind speeds.  No seasonal dependency can be detected for the underestimation of the spectra from the modelled data. The shape can well be modelled by the approach of [Larsén et al., 2013].  Concerning the coherences, the tendency of an overestimation as detected in the analysis of annual sets, shows up in the seasonal scale in similar magnitude, reflecting a systematic shortcoming of the simulated sets to reflect the spatial inhomogeneity of the field.</p><p>[1] Poulsen, T, Beyer, H.G., Cross spectral characteristics of  modelled and measured sets of spatially distributed wind in the Faroe Islands, poster presentation  EGU 2020 (2020)</p><p>[2] Larsén, X., Vincent, C., and Larsen, S. (2013). Spectral structure of mesoscale wind over the water. Quarterly Journal of the Royal Meteorological Society, 139:685–700. (2013)</p>

scholarly journals A Comparative Analysis of the Wind and Wave Climate in the Black Sea Along the Shipping Routes

Water ◽  
2018 ◽  
Vol 10 (7) ◽  
pp. 924 ◽  
Author(s):  
Liliana Rusu ◽  
Alina Raileanu ◽  
Florin Onea
Keyword(s):  
Regional Climate Model ◽  
Black Sea ◽  
Climate Model ◽  
Extreme Values ◽  
Regional Climate ◽  
Wave Model ◽  
Wave Climate ◽  
Reanalysis Data ◽  
The Black Sea ◽  
Wind Fields

The aim of the present work is to assess the wind and wave climate in the Black Sea while considering various data sources. A special attention is given to the areas with higher navigation traffic. Thus, the results are analyzed for the sites located close to the main harbors and also along the major trading routes. The wind conditions were evaluated considering two different data sets, the reanalysis data provided by NCEP-CFSR (U.S. National Centers for Environmental Prediction-Climate Forecast System Reanalysis) and the hindcast results given by a Regional Climate Model (RCM) that were retrieved from EURO-CORDEX (European Domain-Coordinated Regional Climate Downscaling Experiment). For the waves, there were considered the results coming from simulations with the SWAN (Simulating Wave Nearshore) model, forced with the above-mentioned two different wind fields. Based on these results, it can be mentioned that the offshore sites seem to show the best correlation between the two datasets for both wind and waves. As regards the nearshore sites, there is a good agreement between the average values of the wind data that are provided by the different datasets, except for the points located in the southern part of the Black Sea. The same trends noticed for the average values remain also valid for the extreme values. Finally, it can be concluded that the results obtained in this study are useful for the evaluation of the wind and wave climate in the Black Sea. Also, they give a more comprehensive picture on how well the wind field provided by the Regional Climate Model, and the wave model forced with this wind, can represent the features of a complex marine environment as the Black Sea is.

scholarly journals Seasonal thermal regime and climatic trends in lakes of the Tibetan highlands

2017 ◽  
Vol 21 (4) ◽  
pp. 1895-1909 ◽  
Author(s):  
Georgiy Kirillin ◽  
Lijuan Wen ◽  
Tom Shatwell
Keyword(s):  
Tibetan Plateau ◽  
High Altitude ◽  
Air Temperature ◽  
Thermal Regime ◽  
Mixed Boundary ◽  
Reanalysis Data ◽  
Shortwave Radiation ◽  
The Tibetan Plateau ◽  
Seasonal Temperature ◽  
High Altitude Lakes

Abstract. The hydrology of the lake-rich Tibetan Plateau is important for the global climate, yet little is known about the thermal regime of Tibetan lakes due to scant data. We (i) investigated the characteristic seasonal temperature patterns and recent trends in the thermal and stratification regimes of lakes on the Tibetan Plateau and (ii) tested the performance of the one-dimensional lake parameterization scheme FLake for the Tibetan lake system. For this purpose, we combined 3 years of in situ lake temperature measurements, several decades of satellite observations, and the global reanalysis data. We chose the two largest freshwater Tibetan lakes, Ngoring and Gyaring, as study sites. The lake model FLake faithfully reproduced the specific features of the high-altitude lakes and was subsequently applied to reconstruct the vertically resolved heat transport in both lakes during the last 4 decades. The model suggested that Ngoring and Gyaring were ice-covered for about 6 months and stratified in summer for about 4 months per year with a short spring overturn and a longer autumn overturn. In summer the surface mixed boundary layer extended to 6–8 m of depth and was about 20 % shallower in the more turbid Gyaring. The thermal regime of the transparent Ngoring responded more strongly to atmospheric forcing than Gyaring, where the higher turbidity damped the response. According to the reanalysis data, air temperatures and humidity have increased, whereas solar radiation has decreased, since the 1970s. Surprisingly, the modeled mean lake temperatures did not change, nor did the phenology of the ice cover or stratification. Lake surface temperatures in summer increased only marginally. The reason is that the increase in air temperature was offset by the decrease in radiation, probably due to increasing humidity. This study demonstrates that air temperature trends are not directly coupled to lake temperatures and underscores the importance of shortwave radiation for the thermal regime of high-altitude lakes.

Influence of the Wind Fields on the Accuracy of Numerical Wave Modelling in Offshore Locations

2008 ◽  
Author(s):  
Liliana Rusu ◽  
Mariana Bernardino ◽  
C. Guedes Soares
Keyword(s):  
Numerical Models ◽  
Atmospheric Model ◽  
Reanalysis Data ◽  
Wave Direction ◽  
Wind Fields ◽  
Large Area ◽  
Point Of Interest ◽  
Area Of Interest ◽  
Wave Boundary

The influence of the wind field resolution in the accuracy of the wave predictions is studied using spectral numerical models in highly non-stationary situations. The main area of interest is the port of Sines, located in the Portuguese continental coastal environment south of Lisbon. An implementation of the MM5 atmospheric model was developed for the area of study, starting from a large area of the Atlantic Ocean and nesting successively with finer grid towards the point of interest, so as to provide wind fields with increasing level of detail. The SWAN model was forced with wind fields simulated by different models and with different resolutions. A wave rider type directional buoy located offshore the Sines port at approximately 100 meters water depth was used as check point. In a first approach, two different wind fields simulated by REMO and MM5 were considered for forcing the SWAN based transformation module. Both wind fields have a spatial resolution of 0.5 degrees and were obtained using the global NCEP reanalysis data as wind driver. Initial wave boundary conditions are provided by WAM simulations for the entire North Atlantic basin. Afterwards, three successive SWAN areas were implemented. The three spatial resolutions defined for these SWAN computational domains were 0.05, 0.02 and 0.005 degrees. Corresponding special resolutions for the wind fields produced by MM5 ranged from 0.15 to 0.015 degrees. Simulations were performed from the beginning of December 2000 till the end of February 2001, which is one of the most energetic periods registered close to this coast and the results in terms of significant wave height, mean period and wave direction were compared with the in situ measured data.

scholarly journals A study of the dynamical characteristics of inertia–gravity waves in the Antarctic mesosphere combining the PANSY radar and a non-hydrostatic general circulation model

2018 ◽  
Author(s):  
Ryosuke Shibuya ◽  
Kaoru Sato
Keyword(s):  
General Circulation Model ◽  
Gravity Waves ◽  
General Circulation ◽  
Initial Conditions ◽  
Circulation Model ◽  
Reanalysis Data ◽  
Wind Fields ◽  
High Latitude Region ◽  
The Antarctic ◽  
Inertia Gravity Waves

Abstract. The first long-term simulation using the high-top non-hydrostatic general circulation model (NICAM) was executed to analyze mesospheric gravity waves in the period from April to August in 2016. Successive runs lasting 7 days are performed using initial conditions from the MERRA reanalysis data with an overlap of 2 days between consecutive runs. The data for the analyses were compiled from the last 5 days of each run. The simulated wind fields were closely compared to the MERRA reanalysis data and to the observational data collected by a complete PANSY (Program of the Antarctic Syowa MST/IS Radar) radar system installed at Syowa Station (39.6° E 69.0° S). It is shown that the NICAM mesospheric wind fields are realistic, even though the amplitudes of the wind disturbances appear to be larger than the radar observations. The power spectrum of the meridional wind fluctuations at a height of 70 km has an isolated and broad peak at frequencies slightly lower than the inertial frequency, f, for latitudes from 30° S to 75° S, while another isolated peak is observed at frequencies of approximately 2π/8 h at latitudes from 78° S to 90° S. The spectrum of the vertical fluxes of the zonal momentum also has an isolated peak at frequencies slightly lower than f at latitudes from 30° S to 75° S at a height of 70 km. It is shown that these isolated peaks are primarily composed of gravity waves with horizontal wavelengths of more than 1000 km. The latitude–height structure of the momentum fluxes indicates that the isolated peaks at frequencies slightly lower than f originate from two branches of gravity wave propagation paths. It is thought that one branch originates from 75° S due to topographic gravity waves generated over the Antarctic Peninsula and its coast, while more than 80 % of the other branch originates from 45° S and includes contributions by non-orographic gravity waves. The existence of isolated peaks in the high-latitude region in the mesosphere is likely explained by the poleward propagation of quasi-inertia–gravity waves and by the accumulation of wave energies near the inertial frequency at each latitude.

scholarly journals Two Contrasting African Easterly Wave Behaviors

2019 ◽  
Vol 76 (6) ◽  
pp. 1753-1768 ◽  
Author(s):  
Yuan-Ming Cheng ◽  
Chris D. Thorncroft ◽  
George N. Kiladis
Keyword(s):  
Wave Train ◽  
Wave Structure ◽  
Meridional Wind ◽  
Reanalysis Data ◽  
Equatorial Region ◽  
Checkerboard Pattern ◽  
Wind Fields ◽  
Easterly Waves ◽  
State Potential ◽  
The Tropics

Abstract The dominant structural variability of African easterly waves (AEWs) is explored using an empirical orthogonal function (EOF) approach. The structure of AEWs is obtained by projecting the wind fields from reanalysis data and satellite-derived brightness temperature Tb onto the principal components associated with EOF patterns of filtered Tb (Tb EOF) and 700-hPa meridional wind (v700 EOF). The wave structure depicted by the Tb EOF has confined convection and circulation mostly south of the African easterly jet. It shares many characteristics with AEWs analyzed and discussed in the literature. In contrast, the v700 EOF exhibits less familiar characteristics and includes interactions with the equatorial and subtropical regions. The convective patterns are characterized by a “checkerboard” pattern of convection that has not been emphasized before. The most striking feature is the broad meridional extent, which depicts interactions with a mixed Rossby–gravity wave (MRG) in the equatorial region and interactions with the basic-state potential vorticity in the subtropics. The southern portion of the wave has a modified MRG structure, and this AEW–MRG hybrid cannot be separated using the EOF technique, indicating the prevalence of such structures. The subtropical interaction at mid- to lower levels establishes a vortex off the coast of Morocco that results in dry-air advection into the tropics in tandem with the northern vortex. At upper levels, a subtropical wave train is induced by the AEW-associated convective inflow and outflow. The contrasting AEW circulations are associated with differences in the precipitation rates and patterns over Africa. These results highlight the variability of AEW structures and their interactions with equatorial and subtropical waves.

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