Twenty first century changes in Antarctic and Southern Ocean surface climate in CMIP6

Two decades into the 21st century there is growing evidence for global impacts of Antarctic and Southern Ocean climate change. Reliable estimates of how the Antarctic climate system would behave under a range of scenarios of future external climate forcing are thus a high priority. Output from new model simulations coordinated as part of the Coupled Model Intercomparison Project Phase 6 (CMIP6) provides an opportunity for a comprehensive analysis of the latest generation of state‐of‐the‐art climate models following a wider range of experiment types and scenarios than previous CMIP phases. Here the main broad‐scale 21st century Antarctic projections provided by the CMIP6 models are shown across four forcing scenarios: SSP1‐2.6, SSP2‐4.5, SSP3‐7.0 and SSP5‐8.5. End‐of‐century Antarctic surface‐air temperature change across these scenarios (relative to 1995–2014) is 1.3, 2.5, 3.7 and 4.8°C. The corresponding proportional precipitation rate changes are 8, 16, 24 and 31%. In addition to these end‐of‐century changes, an assessment of scenario dependence of pathways of absolute and global‐relative 21st century projections is conducted. Potential differences in regional response are of particular relevance to coastal Antarctica, where, for example, ecosystems and ice shelves are highly sensitive to the timing of crossing of key thresholds in both atmospheric and oceanic conditions. Overall, it is found that the projected changes over coastal Antarctica do not scale linearly with global forcing. We identify two factors that appear to contribute: (a) a stronger global‐relative Southern Ocean warming in stabilisation (SSP2‐4.5) and aggressive mitigation (SSP1‐2.6) scenarios as the Southern Ocean continues to warm and (b) projected recovery of Southern Hemisphere stratospheric ozone and its effect on the mid‐latitude westerlies. The major implication is that over coastal Antarctica, the surface warming by 2100 is stronger relative to the global mean surface warming for the low forcing compared to high forcing future scenarios

Antarctic Sea Ice Area in CMIP6

Fully coupled climate models have long shown a wide range of Antarctic sea ice states and evolution over the satellite era. Here, we present a high‐level evaluation of Antarctic sea ice in 40 models from the most recent phase of the Coupled Model Intercomparison Project (CMIP6). Many models capture key characteristics of the mean seasonal cycle of sea ice area (SIA), but some simulate implausible historical mean states compared to satellite observations, leading to large intermodel spread. Summer SIA is consistently biased low across the ensemble. Compared to the previous model generation (CMIP5), the intermodel spread in winter and summer SIA has reduced, and the regional distribution of sea ice concentration has improved. Over 1979–2018, many models simulate strong negative trends in SIA concurrently with stronger‐than‐observed trends in global mean surface temperature (GMST). By the end of the 21st century, models project clear differences in sea ice between forcing scenarios

Attenuation of ocean surface waves in pancake and frazil sea ice along the coast of the Chukchi Sea

Alaskan Arctic coastlines are protected seasonally from ocean waves by the presence of coastal and shorefast sea ice. This study presents field observations collected during the autumn 2019 freeze up near Icy Cape, a coastal headland in the Chukchi Sea of the Western Arctic. The evolution of the coupled air-ice-ocean-wave system during a four-day wave event was monitored using drifting wave buoys, a cross-shore mooring array, and ship-based measurements. The incident wave field with peak period of 2.5 s was attenuated by coastal pancake and frazil sea ice, reducing significant wave height by 40\% over less than 5 km of cross-shelf distance spanning water depths from 13 to 30 m. Spectral attenuation coefficients are evaluated with respect to wave and ice conditions and the proximity to the ice edge. Attenuation rates are found to be three times higher within 500 m of the ice edge, relative to values farther in the ice cover. Attenuation coefficients are in the range of $\langle 2.3,2.7\rangle$ \si{\meter^{-1}}, and follow a power-law dependence on frequency

Asymmetry in the Seasonal Cycle of Zonal‐Mean Surface Air Temperature

Abstract: At most latitudes, the seasonal cycle of zonal‐mean surface air temperature is notably asymmetric: the length of the warming season is not equal to the length of the cooling season. The asymmetry varies spatially, with the cooling season being ∼40 days shorter than the warming season in the subtropics and the warming season being ∼100 days shorter than the cooling season at the poles. Furthermore, the asymmetry differs between the Northern Hemisphere and the Southern Hemisphere. Here, we show that these observed features are broadly captured in a simple model for the evolution of temperature forced by realistic insolation. The model suggests that Earth's orbital eccentricity largely determines the hemispheric contrast, and obliquity broadly dictates the meridional structure. Clouds, atmospheric heat flux convergence, and time‐invariant effective surface heat capacity have minimal impacts on seasonal asymmetry. This simple, first‐order picture has been absent from previous discussions of the surface temperature seasonal cycle

CICE-Consortium/Icepack: Icepack 1.4.0

&lt;p&gt;Icepack version 1.4.0 is being released with CICE6.5.0. This is a major release update from the Icepack1.3.4 release of September 2023. This update includes the first of a series of updates to Icepack as a result of coupling into E3SM. Some of the interfaces have changed, some new parameters were added, the 5-band snicar shortwave feature was added, the frazil ice coupling was updated, and a bug was fixed in the lateral/bottom melting term that doesn't impact science.&lt;/p&gt;&lt;p&gt;&lt;strong&gt;Major Changes&lt;/strong&gt;&lt;/p&gt;&lt;ul&gt;&lt;li&gt;Merge E3SM initial integration branch &lt;a href="https://urldefense.com/v3/__https://github.com/CICE-Consortium/Icepack/pull/460__;!!Bt8fGhp8LhKGRg!CLZ0aB38I8HlLa96QMIOU2K0XVT5gjSSQNU7RQRFDwCxaNOc8l30fOV570hHRxBXztOe0T-Q2_LuRpPcf3KHRZ4">#460</a>, <a href="https://urldefense.com/v3/__https://github.com/CICE-Consortium/Icepack/pull/468__;!!Bt8fGhp8LhKGRg!CLZ0aB38I8HlLa96QMIOU2K0XVT5gjSSQNU7RQRFDwCxaNOc8l30fOV570hHRxBXztOe0T-Q2_LuRpPc8APqxwg"&gt;#468&lt;/a&gt;, &lt;a href="https://urldefense.com/v3/__https://github.com/CICE-Consortium/Icepack/pull/469__;!!Bt8fGhp8LhKGRg!CLZ0aB38I8HlLa96QMIOU2K0XVT5gjSSQNU7RQRFDwCxaNOc8l30fOV570hHRxBXztOe0T-Q2_LuRpPctLVZblg">#469</a><ul><li>update dEdd shortwave, including new hardcoded lookup tables, 3-band and 5-band options, and support for 'dEdd_snicar_ad' as a shortwave option. Add NO_SNICARHC to turn off large hardcoded 5-band data table during compilation to save compilation time. That table is only needed with shortwave='dEdd_snicar_ad' when snw_ssp_table='snicar' but is included in compilation by default.</li><li>Update modal aerosols (<strong>Changes modal aerosol results in Icepack</strong>)</li><li>Update public interfaces (<strong>Impacts backward compatibility</strong>)<ul><li>remove nspint public parameters</li><li>add icepack_init_radiation, icepack_salinity_profile, icepack_enthalpy_mush, icepack_warnings_getall</li><li>modify icepack_prep_radiation, remove scalar parameters (ncat, nilyr, nslyr)</li><li>modify icepack_step_radiation, remove scalar parameters (ncat, nblyr, nilyr, nslyr, dEdd_algae, calendar_type, days_per_year, nextsw_cday, modal_aero), remove snicar table data arguments</li><li>add Tf argument to icepack_compute_tracers, icepack_aggregate, icepack_step_ridge,</li></ul></li><li>Update icepack parameters, add hi_min, Tliquidus_max, snw_ssp_table, 'dEdd_snicar_ad' option to shortwave, 'constant' to tfrz_option</li><li>Update the Tf implementation to make values internally consistent. Remove hardcoded Tocnfrz in a couple places, add tfrz_option='constant' which sets Tf to Tocnfrz. (<strong>Changes answers in some cases, can also change the value of temperature in restart at non-ice gridcells even though the ice state is identical</strong>)</li><li>Modify iDin computation in subroutine compute_microS_mushy</li><li>Fix fhtan computation in compute_albedos</li><li>Refactor internal subroutine arguments to leverage module data more</li><li>Rename orbital interfaces from shr_orb to icepack_orb to more clearly differentiate internal and external versions</li><li>Update some optional argument handling</li><li>Clean up Icepack driver namelist logging</li></ul></li></ul><p><strong>Bug fixes</strong></p><ul><li>Fix bug in frzmlt_bottom_lateral to limit the amount of heat available for melting <a href="https://urldefense.com/v3/__https://github.com/CICE-Consortium/Icepack/pull/474__;!!Bt8fGhp8LhKGRg!CLZ0aB38I8HlLa96QMIOU2K0XVT5gjSSQNU7RQRFDwCxaNOc8l30fOV570hHRxBXztOe0T-Q2_LuRpPc3HTe860"&gt;#474&lt;/a&gt;&lt;/li&gt;&lt;/ul&gt;&lt;p&gt;&lt;strong&gt;Enhancements&lt;/strong&gt;&lt;/p&gt;&lt;ul&gt;&lt;li&gt;Generalize the logic for coupling frazil ice. Add namelist cpl_frazil and add update_ocn_f to icepack_parameters. &lt;a href="https://urldefense.com/v3/__https://github.com/CICE-Consortium/Icepack/pull/458__;!!Bt8fGhp8LhKGRg!CLZ0aB38I8HlLa96QMIOU2K0XVT5gjSSQNU7RQRFDwCxaNOc8l30fOV570hHRxBXztOe0T-Q2_LuRpPc0IG-Ooc">#458</a></li><li>Update the implementation of the rsnw interpolation in dEdd shortwave code, add new methods shortwave_search, add support for 5-band test data, and update the 5-band interpolation to be linear (<strong>Non-climate answer changing for shortwave='dEdd_snicar_ad', passes QC</strong>) <a href="https://urldefense.com/v3/__https://github.com/CICE-Consortium/Icepack/pull/472__;!!Bt8fGhp8LhKGRg!CLZ0aB38I8HlLa96QMIOU2K0XVT5gjSSQNU7RQRFDwCxaNOc8l30fOV570hHRxBXztOe0T-Q2_LuRpPcenSZJys"&gt;#472&lt;/a&gt;&lt;/li&gt;&lt;li&gt;Add icepack parameter tscale_pnd_drain, sets the timescale (in days) for macroscopic drainage when using mushy thermodynamics. &lt;a href="https://urldefense.com/v3/__https://github.com/CICE-Consortium/Icepack/pull/462__;!!Bt8fGhp8LhKGRg!CLZ0aB38I8HlLa96QMIOU2K0XVT5gjSSQNU7RQRFDwCxaNOc8l30fOV570hHRxBXztOe0T-Q2_LuRpPcdI0HE4g">#462</a></li><li>Update picard_nonconvergence diagnostics <a href="https://urldefense.com/v3/__https://github.com/CICE-Consortium/Icepack/pull/464__;!!Bt8fGhp8LhKGRg!CLZ0aB38I8HlLa96QMIOU2K0XVT5gjSSQNU7RQRFDwCxaNOc8l30fOV570hHRxBXztOe0T-Q2_LuRpPcqEytN64"&gt;#464&lt;/a&gt;&lt;/li&gt;&lt;li&gt;Add readthedocs yaml for documentation building &lt;a href="https://urldefense.com/v3/__https://github.com/CICE-Consortium/Icepack/pull/466__;!!Bt8fGhp8LhKGRg!CLZ0aB38I8HlLa96QMIOU2K0XVT5gjSSQNU7RQRFDwCxaNOc8l30fOV570hHRxBXztOe0T-Q2_LuRpPcOXe-eWI">#466</a></li><li>Remove unncessary call to icepack_recompute_constants in icepack_query_parameters <a href="https://urldefense.com/v3/__https://github.com/CICE-Consortium/Icepack/pull/465__;!!Bt8fGhp8LhKGRg!CLZ0aB38I8HlLa96QMIOU2K0XVT5gjSSQNU7RQRFDwCxaNOc8l30fOV570hHRxBXztOe0T-Q2_LuRpPcfvRYWtE"&gt;#465&lt;/a&gt;&lt;/li&gt;&lt;li&gt;Port to Perlmutter &lt;a href="https://urldefense.com/v3/__https://github.com/CICE-Consortium/Icepack/pull/467__;!!Bt8fGhp8LhKGRg!CLZ0aB38I8HlLa96QMIOU2K0XVT5gjSSQNU7RQRFDwCxaNOc8l30fOV570hHRxBXztOe0T-Q2_LuRpPcImXXHUs">#467</a></li><li>Update Derecho inputdata path <a href="https://urldefense.com/v3/__https://github.com/CICE-Consortium/Icepack/pull/471__;!!Bt8fGhp8LhKGRg!CLZ0aB38I8HlLa96QMIOU2K0XVT5gjSSQNU7RQRFDwCxaNOc8l30fOV570hHRxBXztOe0T-Q2_LuRpPch5DJQBM"&gt;#471&lt;/a&gt;&lt;/li&gt;&lt;li&gt;Fix script bug in icepack.launch.csh &lt;a href="https://urldefense.com/v3/__https://github.com/CICE-Consortium/Icepack/pull/475__;!!Bt8fGhp8LhKGRg!CLZ0aB38I8HlLa96QMIOU2K0XVT5gjSSQNU7RQRFDwCxaNOc8l30fOV570hHRxBXztOe0T-Q2_LuRpPceI3hfOU">#475</a></li></ul><p><strong>Documentation</strong></p><ul><li>Update version <a href="https://urldefense.com/v3/__https://github.com/CICE-Consortium/Icepack/pull/473__;!!Bt8fGhp8LhKGRg!CLZ0aB38I8HlLa96QMIOU2K0XVT5gjSSQNU7RQRFDwCxaNOc8l30fOV570hHRxBXztOe0T-Q2_LuRpPcydgNBr8"&gt;#473&lt;/a&gt;&lt;/li&gt;&lt;li&gt;Update documentation &lt;a href="https://urldefense.com/v3/__https://github.com/CICE-Consortium/Icepack/pull/460__;!!Bt8fGhp8LhKGRg!CLZ0aB38I8HlLa96QMIOU2K0XVT5gjSSQNU7RQRFDwCxaNOc8l30fOV570hHRxBXztOe0T-Q2_LuRpPcf3KHRZ4">#460</a>, <a href="https://urldefense.com/v3/__https://github.com/CICE-Consortium/Icepack/pull/466__;!!Bt8fGhp8LhKGRg!CLZ0aB38I8HlLa96QMIOU2K0XVT5gjSSQNU7RQRFDwCxaNOc8l30fOV570hHRxBXztOe0T-Q2_LuRpPcOXe-eWI"&gt;#466&lt;/a&gt;, &lt;a href="https://urldefense.com/v3/__https://github.com/CICE-Consortium/Icepack/pull/470__;!!Bt8fGhp8LhKGRg!CLZ0aB38I8HlLa96QMIOU2K0XVT5gjSSQNU7RQRFDwCxaNOc8l30fOV570hHRxBXztOe0T-Q2_LuRpPcbqRymmc">#470</a>, <a href="https://urldefense.com/v3/__https://github.com/CICE-Consortium/Icepack/pull/473__;!!Bt8fGhp8LhKGRg!CLZ0aB38I8HlLa96QMIOU2K0XVT5gjSSQNU7RQRFDwCxaNOc8l30fOV570hHRxBXztOe0T-Q2_LuRpPcydgNBr8"&gt;#473&lt;/a&gt;&lt;/li&gt;&lt;/ul&gt

CICE-Consortium/Icepack: Icepack 1.3.4

Icepack version 1.3.4 is being released with CICE6.4.2. This is a minor release update from the Icepack1.3.3 release from December, 2022. This update includes several bug fixes including in snow physics, FSD lateral melt, and treatment of thin ice/snow enthalpy. It also includes improvements to the treatment of optional arguments in the public interfaces, capability for netcdf restart files, and other enhancements. Bug fixes Correct thin ice/snow treatment of enthalpy and other tracers. #454. This changes answers in CICE (QC passes) but not Icepack Fix ice area inconsistency under convergence in single column mode #433. This changes answers in standalone Icepack but not in CICE. Fix bug in snow sublimation in icepack_therm_vertical #428. Fix bug in smicen and smliqn calculation in thermo_vertical #449. This changes answers for snwgrain configurations. Update the FSD lateral heat flux computation and fix bug in the welding scheme. #424 #435 This changes answers for FSD configurations. Fix bug in history file output related to FSD. #421. This does not change model results. Fix bug in start time for netCDF history output #426. This does not change model results. Update hsn_new(1) computation in snow_redist. This does not change model results. Enhancements Update snow physics logic control #449 Refactor implementation of optional arguments for isotopes, snwgrain, therm1 and therm2 as well as some optional outputs in Icepack public interfaces #423, #429. Update FSD arguments, convert them to optional #440. Clean up optional argument attributes and update optional argument documentation #443. Add icepack_chkoptargflag function #423, #434 Add support for netCDF restart files, update history and restart format control #427 Deprecate zsalinity #448 Remove ridging iteration log output #445, #446 Check allocation of snow aging tables better #428 Clean up some intent statements, clean up public interface declarations #429 Shift a few left-over print statements to use the icepack warning infrastructure #424 Add support for netCDF with conda_linux #425 Update icepack_write_parameters and add call in Icepack #436 Update ports to Onyx, Derecho, Cheyenne, Chicoma #442, #449, #456 Documentation Update version, License, Copyright date #457 Explicitly turn on pdf generation in readthedocs #438 Updates needed for compatibility with changes in readthedocs #432 Update documentation #427, #429, #433, #435, #437, #440, #443, #448, #45