Franziska Hellmuth
\n", "NEGI course 2019 - eScience for linking Arctic measurements and modeling
\n", "Group assistants: Paul Glantz, Ksenia Tabakova, Jonas Gliss
\n", " " ] }, { "cell_type": "markdown", "metadata": {}, "source": [ "# Abstract \n", "We compare aerosol optical depth (AOD) from 12 Coupled Model Intercomparison Project 6 (CMIP6) models with Modern-Era Retrospective analysis for Research and Applications 2 (MERRA2) and ground-based observational data from the AErosol RObotic NETwork (AERONET) in the Arctic and zonally. We find that MERRA2 satellite reanalysis is too high compared to the Sunphotometer measurements. Seasonal variation of AOD over the last 34 years was mostly not reproduced by the 12 CMIP6 models. CanESM5 and GFDL-CM4 simulated AOD values within the MERRA2 variability during Arctic spring. MERRA2 reanalysis shows a decrease of AOD in the Northern Hemisphere since 1980. GFDL-ESM4 and GFDL-CM4 simulated the zonally averaged AOD within the MERRA2 reanalysis. NorESM-LM2 has too much sea salt in the Southern Hemisphere (50$^\\circ$S) and too little AOD above 40$^\\circ$N. Further work has to be done to clarify the contribution and representation of sea salt in NorESM-LM2." ] }, { "cell_type": "markdown", "metadata": {}, "source": [ "# Introduction\n", "It has long been known that the Arctic region is particularly sensitive to global warming (Collins et al., 2013). Atmospheric Aerosols are particles suspended in the air. Some Aerosols have been produced by natural processes others by human activities. Aerosols in the Atmosphere reduce the amount of incoming solar radiation by scattering or absorbing light of solar radiation. The amount of atmospheric Aerosols varies with location, time and due to events such as dust storms, forest fires and volcanic eruptions (Lohmann et al., 2016). \n", "In a warming climate, will the sea ice decrease and larger areas of open water will follow an increase in organic aerosol uptake. Aerosols (natural or anthropogenic) can affect the Earth climate through interaction with solar radiation and clouds. Aerosol optical depth (AOD) is a measure of the amount of sunlight that has been scattered or absorbed. \n", "\n", "The largest ground-based AOD measurement project is the AErosol RObotic NETwork (AERONET). The Sunphotometers are distributed over the globe and can give information about the distribution of aerosols in the atmosphere. This measurements are sparse and represent the AOD distribution only for a small area. With the launch of satellites, it is possible to retrieve global estimates of aerosol optical depth. Cloud free daily data can be used to reanalyse the AOD in a finer grid-scale and use it to validate global climate model performance to predict the changing climate more accurately. \n", "\n", "Glantz et al., 2014 analysed the AOD in the Svalbard area. They compared Moderate Resolution Imaging Spectroradiometer (MODIS) Aqua retrievals of AOD to Sunphotometer measurements from Svalbard. The study shows that the Svalbard region undergoes a seasonal cycle with higher AOD during spring and a low AOD during summer. The remote sensing data is then used to examine the AOD generation of global climate models, represented in the Coupled Model Intercomparison Project 5 (CMIP5). In the 1980 - 2014 period show the CMIP5 models an underestimation of AOD during spring and an overestimation during summer when compared to remote sensing data.\n", "\n", "In the presented study nine years of Modern-Era Retrospective analysis for Research and Applications 2 (MERRA2), satellite reanalysis is compared to ground-based Sunphotometer AOD measurements in the Arctic. Afterwards, are climate model simulations from CMIP6 examined in comparison to MERRA2 satellite reanalysis over 34 years.\n", "\n", "The following questions have been addressed:\n", "1. How representative are MERRA2 satellite reanalysis in comparison to the ground-based AOD observations in the Arctic?\n", "2. How accurately does the global climate models of CMIP6 simulate the AOD for the Arctic and zonally for the last three decades?\n", "\n", "[Section 2.1](#AERONET-Sunphotometer) and [Section 2.2](#MERRA2) contains the code to read the observational data from the Sunphotmeters and the MERRA2 satellite reanalysis in the Arctic region, respectively. [Section 2.3](#CMIP6) consists of the code for finding the AOD at 550nm in the CMIP6 models and their ensembles. [Section 3](#Results-and-Discussion) will then present the results to answer the questions above." ] }, { "cell_type": "markdown", "metadata": {}, "source": [ "# Ground-based, satellite reanalysis and CMIP model data\n", "Global climate models are essential to study future climate changes of aerosols and clouds. \n", "Aerosol optical depth (AOD) at 550nm from Sunphotometer measurements from Aerosol Robotic Network (AERONET) is used as the reference to satellite retrieved reanalysis MERRA2. Then, AOD satellite reanalysis is utilised with comparable aerosol properties from historical Phase 6 of the CMIP6 model runs. The CMIP6 includes 33 participating model groups (Eyring et al., 2016) and data is available through the CMIP6 search interface https://esgf-data.dkrz.de/search/cmip6-dkrz/. Of these 33 models, we focus on twelve models to evaluate the AOD. The model specifications can be found in Table 1.\n", "\n", "\n",
"Client\n", "
| \n",
"\n",
"Cluster\n", "
| \n",
"
| \n", " | M_Arctic | \n", "
|---|---|
| time | \n", "\n", " |
| 1980-01-01 | \n", "0.104969 | \n", "
| 1980-02-01 | \n", "0.103549 | \n", "
| 1980-03-01 | \n", "0.110453 | \n", "
| 1980-04-01 | \n", "0.109904 | \n", "
| 1980-05-01 | \n", "0.109821 | \n", "
| \n", " | M_Arctic | \n", "M_Svalbard | \n", "
|---|---|---|
| time | \n", "\n", " | \n", " |
| 1980-01-01 | \n", "0.104969 | \n", "0.116562 | \n", "
| 1980-02-01 | \n", "0.103549 | \n", "0.093377 | \n", "
| 1980-03-01 | \n", "0.110453 | \n", "0.147553 | \n", "
| 1980-04-01 | \n", "0.109904 | \n", "0.123854 | \n", "
| 1980-05-01 | \n", "0.109821 | \n", "0.119110 | \n", "