Evaluation of Southern Ocean cloud in the HadGEM3 general circulation model and MERRA-2 reanalysis using ship-based observations
Southern Ocean (SO) shortwave (SW) radiation biases are a common problem in contemporary general circulation models (GCMs), with most models exhibiting a tendency to absorb too much incoming SW radiation. These biases have been attributed to deficiencies in the representation of clouds during the au...
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ftcopernicus:oai:publications.copernicus.org:acp74981 2023-05-15T18:07:34+02:00 Evaluation of Southern Ocean cloud in the HadGEM3 general circulation model and MERRA-2 reanalysis using ship-based observations Kuma, Peter McDonald, Adrian J. Morgenstern, Olaf Alexander, Simon P. Cassano, John J. Garrett, Sally Halla, Jamie Hartery, Sean Harvey, Mike J. Parsons, Simon Plank, Graeme Varma, Vidya Williams, Jonny 2020-06-05 application/pdf https://doi.org/10.5194/acp-20-6607-2020 https://www.atmos-chem-phys.net/20/6607/2020/ eng eng doi:10.5194/acp-20-6607-2020 https://www.atmos-chem-phys.net/20/6607/2020/ eISSN: 1680-7324 Text 2020 ftcopernicus https://doi.org/10.5194/acp-20-6607-2020 2020-06-08T16:22:00Z Southern Ocean (SO) shortwave (SW) radiation biases are a common problem in contemporary general circulation models (GCMs), with most models exhibiting a tendency to absorb too much incoming SW radiation. These biases have been attributed to deficiencies in the representation of clouds during the austral summer months, either due to cloud cover or cloud albedo being too low. The problem has been the focus of many studies, most of which utilised satellite datasets for model evaluation. We use multi-year ship-based observations and the CERES spaceborne radiation budget measurements to contrast cloud representation and SW radiation in the atmospheric component Global Atmosphere (GA) version 7.1 of the HadGEM3 GCM and the MERRA-2 reanalysis. We find that the prevailing bias is negative in GA7.1 and positive in MERRA-2. GA7.1 performs better than MERRA-2 in terms of absolute SW bias. Significant errors of up to 21 W m −2 (GA7.1) and 39 W m −2 (MERRA-2) are present in both models in the austral summer. Using ship-based ceilometer observations, we find low cloud below 2 km to be predominant in the Ross Sea and the Indian Ocean sectors of the SO. Utilising a novel surface lidar simulator developed for this study, derived from an existing Cloud Feedback Model Intercomparison Project (CFMIP) Observation Simulator Package (COSP) – active remote sensing simulator (ACTSIM) spaceborne lidar simulator, we find that GA7.1 and MERRA-2 both underestimate low cloud and fog occurrence relative to the ship observations on average by 4 %–9 % (GA7.1) and 18 % (MERRA-2). Based on radiosonde observations, we also find the low cloud to be strongly linked to boundary layer atmospheric stability and the sea surface temperature. GA7.1 and MERRA-2 do not represent the observed relationship between boundary layer stability and clouds well. We find that MERRA-2 has a much greater proportion of cloud liquid water in the SO in austral summer than GA7.1, a likely key contributor to the difference in the SW radiation bias. Our results suggest that subgrid-scale processes (cloud and boundary layer parameterisations) are responsible for the bias and that in GA7.1 a major part of the SW radiation bias can be explained by cloud cover underestimation, relative to underestimation of cloud albedo. Text Ross Sea Southern Ocean Copernicus Publications: E-Journals Austral Indian Merra ENVELOPE(12.615,12.615,65.816,65.816) Ross Sea Southern Ocean Atmospheric Chemistry and Physics 20 11 6607 6630 |
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Open Polar |
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Copernicus Publications: E-Journals |
op_collection_id |
ftcopernicus |
language |
English |
description |
Southern Ocean (SO) shortwave (SW) radiation biases are a common problem in contemporary general circulation models (GCMs), with most models exhibiting a tendency to absorb too much incoming SW radiation. These biases have been attributed to deficiencies in the representation of clouds during the austral summer months, either due to cloud cover or cloud albedo being too low. The problem has been the focus of many studies, most of which utilised satellite datasets for model evaluation. We use multi-year ship-based observations and the CERES spaceborne radiation budget measurements to contrast cloud representation and SW radiation in the atmospheric component Global Atmosphere (GA) version 7.1 of the HadGEM3 GCM and the MERRA-2 reanalysis. We find that the prevailing bias is negative in GA7.1 and positive in MERRA-2. GA7.1 performs better than MERRA-2 in terms of absolute SW bias. Significant errors of up to 21 W m −2 (GA7.1) and 39 W m −2 (MERRA-2) are present in both models in the austral summer. Using ship-based ceilometer observations, we find low cloud below 2 km to be predominant in the Ross Sea and the Indian Ocean sectors of the SO. Utilising a novel surface lidar simulator developed for this study, derived from an existing Cloud Feedback Model Intercomparison Project (CFMIP) Observation Simulator Package (COSP) – active remote sensing simulator (ACTSIM) spaceborne lidar simulator, we find that GA7.1 and MERRA-2 both underestimate low cloud and fog occurrence relative to the ship observations on average by 4 %–9 % (GA7.1) and 18 % (MERRA-2). Based on radiosonde observations, we also find the low cloud to be strongly linked to boundary layer atmospheric stability and the sea surface temperature. GA7.1 and MERRA-2 do not represent the observed relationship between boundary layer stability and clouds well. We find that MERRA-2 has a much greater proportion of cloud liquid water in the SO in austral summer than GA7.1, a likely key contributor to the difference in the SW radiation bias. Our results suggest that subgrid-scale processes (cloud and boundary layer parameterisations) are responsible for the bias and that in GA7.1 a major part of the SW radiation bias can be explained by cloud cover underestimation, relative to underestimation of cloud albedo. |
format |
Text |
author |
Kuma, Peter McDonald, Adrian J. Morgenstern, Olaf Alexander, Simon P. Cassano, John J. Garrett, Sally Halla, Jamie Hartery, Sean Harvey, Mike J. Parsons, Simon Plank, Graeme Varma, Vidya Williams, Jonny |
spellingShingle |
Kuma, Peter McDonald, Adrian J. Morgenstern, Olaf Alexander, Simon P. Cassano, John J. Garrett, Sally Halla, Jamie Hartery, Sean Harvey, Mike J. Parsons, Simon Plank, Graeme Varma, Vidya Williams, Jonny Evaluation of Southern Ocean cloud in the HadGEM3 general circulation model and MERRA-2 reanalysis using ship-based observations |
author_facet |
Kuma, Peter McDonald, Adrian J. Morgenstern, Olaf Alexander, Simon P. Cassano, John J. Garrett, Sally Halla, Jamie Hartery, Sean Harvey, Mike J. Parsons, Simon Plank, Graeme Varma, Vidya Williams, Jonny |
author_sort |
Kuma, Peter |
title |
Evaluation of Southern Ocean cloud in the HadGEM3 general circulation model and MERRA-2 reanalysis using ship-based observations |
title_short |
Evaluation of Southern Ocean cloud in the HadGEM3 general circulation model and MERRA-2 reanalysis using ship-based observations |
title_full |
Evaluation of Southern Ocean cloud in the HadGEM3 general circulation model and MERRA-2 reanalysis using ship-based observations |
title_fullStr |
Evaluation of Southern Ocean cloud in the HadGEM3 general circulation model and MERRA-2 reanalysis using ship-based observations |
title_full_unstemmed |
Evaluation of Southern Ocean cloud in the HadGEM3 general circulation model and MERRA-2 reanalysis using ship-based observations |
title_sort |
evaluation of southern ocean cloud in the hadgem3 general circulation model and merra-2 reanalysis using ship-based observations |
publishDate |
2020 |
url |
https://doi.org/10.5194/acp-20-6607-2020 https://www.atmos-chem-phys.net/20/6607/2020/ |
long_lat |
ENVELOPE(12.615,12.615,65.816,65.816) |
geographic |
Austral Indian Merra Ross Sea Southern Ocean |
geographic_facet |
Austral Indian Merra Ross Sea Southern Ocean |
genre |
Ross Sea Southern Ocean |
genre_facet |
Ross Sea Southern Ocean |
op_source |
eISSN: 1680-7324 |
op_relation |
doi:10.5194/acp-20-6607-2020 https://www.atmos-chem-phys.net/20/6607/2020/ |
op_doi |
https://doi.org/10.5194/acp-20-6607-2020 |
container_title |
Atmospheric Chemistry and Physics |
container_volume |
20 |
container_issue |
11 |
container_start_page |
6607 |
op_container_end_page |
6630 |
_version_ |
1766179784707014656 |