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1. Dried, closed-path eddy covariance method for measuring carbon dioxide flux over sea ice

   https://doi.org/10.5194/amt-11-6075-2018  

   Butterworth, Brian J. ; Else, Brent G. ( January 2018 , Atmospheric Measurement Techniques)

   Abstract. The Arctic marine environment plays an important role inthe global carbon cycle. However, there remain large uncertainties in howsea ice affects air–sea fluxes of carbon dioxide (CO₂), partially dueto disagreement between the two main methods (enclosure and eddy covariance)for measuring CO₂ flux ($F_{\mathrm{CO}{}_{\mathrm{2}}}$). The enclosure method has appearedto produce more credible $F_{\mathrm{CO}{}_{\mathrm{2}}}$ than eddy covariance (EC), but is notsuited for collecting long-term, ecosystem-scale flux datasets in suchremote regions. Here we describe the design and performance of an EC systemto measure $F_{\mathrm{CO}{}_{\mathrm{2}}}$ over landfast sea ice that addresses the shortcomingsof previous EC systems. The system was installed on a 10m tower onQikirtaarjuk Island – a small rock outcrop in Dease Strait located roughly35km west of Cambridge Bay, Nunavut, in the Canadian Arctic Archipelago. Thesystem incorporates recent developments in the field of air–sea gasexchange by measuring atmospheric CO₂ using a closed-path infrared gasanalyzer (IRGA) with a dried sample airstream, thus avoiding the known watervapor issues associated with using open-path IRGAs in low-flux environments.A description of the methods and the results from 4 months of continuousflux measurements from May through August 2017 are presented, highlightingthe winter to summer transition from ice cover to open water. We show thatthe dried, closed-path EC system greatly reduces the magnitude of measured$F_{\mathrm{CO}{}_{\mathrm{2}}}$ compared to simultaneous open-path EC measurements, and for thefirst time reconciles EC and enclosure flux measurements over sea ice. Thisnovel EC installation is capable of operating year-round on solar and windpower, and therefore promises to deliver new insights into the magnitude ofCO₂ fluxes and their driving processes through the annual sea icecycle.

    

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2. High predictability of terrestrial carbon fluxes from an initialized decadal prediction system

   https://doi.org/10.1088/1748-9326/ab5c55  

   Lovenduski, Nicole S. ; Bonan, Gordon B. ; Yeager, Stephen G. ; Lindsay, Keith ; Lombardozzi, Danica L. ( December 2019 , Environmental Research Letters)

   Interannual variations in the flux of carbon dioxide (CO₂) between the land surface and the atmosphere are the dominant component of interannual variations in the atmospheric CO₂growth rate. Here, we investigate the potential to predict variations in these terrestrial carbon fluxes 1–10 years in advance using a novel set of retrospective decadal forecasts of an Earth system model. We demonstrate that globally-integrated net ecosystem production (NEP) exhibits high potential predictability for 2 years following forecast initialization. This predictability exceeds that from a persistence or uninitialized forecast conducted with the same Earth system model. The potential predictability in NEP derives mainly from high predictability in ecosystem respiration, which itself is driven by vegetation carbon and soil moisture initialization. Our findings unlock the potential to forecast the terrestrial ecosystem in a changing environment.

    

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3. Subgrid variations of the cloud water and droplet number concentration over the tropical ocean: satellite observations and implications for warm rain simulations in climate models

   https://doi.org/10.5194/acp-19-1077-2019  

   Zhang, Zhibo ; Song, Hua ; Ma, Po-Lun ; Larson, Vincent E. ; Wang, Minghuai ; Dong, Xiquan ; Wang, Jianwu ( January 2019 , Atmospheric Chemistry and Physics)

   Abstract. One of the challenges inrepresenting warm rain processes in global climate models (GCMs) is relatedto the representation of the subgrid variability of cloud properties, such ascloud water and cloud droplet number concentration (CDNC), and the effectthereof on individual precipitation processes such as autoconversion. Thiseffect is conventionally treated by multiplying the resolved-scale warm rainprocess rates by an enhancement factor (E_q) which is derived fromintegrating over an assumed subgrid cloud water distribution. The assumedsubgrid cloud distribution remains highly uncertain. In this study, we derivethe subgrid variations of liquid-phase cloud properties over the tropicalocean using the satellite remote sensing products from Moderate ResolutionImaging Spectroradiometer (MODIS) and investigate the correspondingenhancement factors for the GCM parameterization of autoconversion rate. Wefind that the conventional approach of using only subgrid variability ofcloud water is insufficient and that the subgrid variability of CDNC, as wellas the correlation between the two, is also important for correctlysimulating the autoconversion process in GCMs. Using the MODIS data whichhave near-global data coverage, we find that E_q shows a strongdependence on cloud regimes due to the fact that the subgrid variability ofcloud water and CDNC is regime dependent. Our analysis shows a significantincrease of E_q from the stratocumulus (Sc) to cumulus (Cu) regions.Furthermore, the enhancement factor E_N due to the subgrid variation ofCDNC is derived from satellite observation for the first time, and resultsreveal several regions downwind of biomass burning aerosols (e.g., Gulf ofGuinea, east coast of South Africa), air pollution (i.e., East China Sea),and active volcanos (e.g., Kilauea, Hawaii, and Ambae, Vanuatu), where theE_N is comparable to or even larger than E_q, suggesting an importantrole of aerosol in influencing the E_N. MODIS observations suggest thatthe subgrid variations of cloud liquid water path (LWP) and CDNC aregenerally positively correlated. As a result, the combined enhancementfactor, including the effect of LWP and CDNC correlation, is significantlysmaller than the simple product of E_q⋅E_N. Given the importanceof warm rain processes in understanding the Earth's system dynamics and watercycle, we conclude that more observational studies are needed to provide abetter constraint on the warm rain processes in GCMs.

    

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4. The Year of Polar Prediction in the Southern Hemisphere (YOPP-SH)

   https://doi.org/10.1175/BAMS-D-19-0255.1  

   Bromwich, David H. ; Werner, Kirstin ; Casati, Barbara ; Powers, Jordan G. ; Gorodetskaya, Irina V. ; Massonnet, François ; Vitale, Vito ; Heinrich, Victoria J. ; Liggett, Daniela ; Arndt, Stefanie ; et al ( October 2020 , Bulletin of the American Meteorological Society)

   null (Ed.)

   Abstract The Year of Polar Prediction in the Southern Hemisphere (YOPP-SH) had a special observing period (SOP) that ran from 16 November 2018 to 15 February 2019, a period chosen to span the austral warm season months of greatest operational activity in the Antarctic. Some 2,200 additional radiosondes were launched during the 3-month SOP, roughly doubling the routine program, and the network of drifting buoys in the Southern Ocean was enhanced. An evaluation of global model forecasts during the SOP and using its data has confirmed that extratropical Southern Hemisphere forecast skill lags behind that in the Northern Hemisphere with the contrast being greatest between the southern and northern polar regions. Reflecting the application of the SOP data, early results from observing system experiments show that the additional radiosondes yield the greatest forecast improvement for deep cyclones near the Antarctic coast. The SOP data have been applied to provide insights on an atmospheric river event during the YOPP-SH SOP that presented a challenging forecast and that impacted southern South America and the Antarctic Peninsula. YOPP-SH data have also been applied in determinations that seasonal predictions by coupled atmosphere–ocean–sea ice models struggle to capture the spatial and temporal characteristics of the Antarctic sea ice minimum. Education, outreach, and communication activities have supported the YOPP-SH SOP efforts. Based on the success of this Antarctic summer YOPP-SH SOP, a winter YOPP-SH SOP is being organized to support explorations of Antarctic atmospheric predictability in the austral cold season when the southern sea ice cover is rapidly expanding. 

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5. The Year of Polar Prediction in the Southern Hemisphere (YOPP-SH)

   https://doi.org/doi.org/10.1175/BAMS-D-19-0255.1  

   Bromwich, D.H. ( October 2020 , Bulletin of the American Meteorological Society)

   null (Ed.)

   The Year of Polar Prediction in the Southern Hemisphere (YOPP-SH) had a Special Observing Period (SOP) that ran from November 16, 2018 to February 15, 2019, a period chosen to span the austral warm season months of greatest operational activity in the Antarctic. Some 2200 additional radiosondes were launched during the 3-month SOP, roughly doubling the routine program, and the network of drifting buoys in the Southern Ocean was enhanced. An evaluation of global model forecasts during the SOP and using its data has confirmed that extratropical Southern Hemisphere forecast skill lags behind that in the Northern Hemisphere with the contrast being greatest between the southern and northern polar regions. Reflecting the application of the SOP data, early results from observing system experiments show that the additional radiosondes yield the greatest forecast improvement for deep cyclones near the Antarctic coast. The SOP data have been applied to provide insights on an atmospheric river event during the YOPP-SH SOP that presented a challenging forecast and that impacted southern South America and the Antarctic Peninsula. YOPP-SH data have also been applied in determinations that seasonal predictions by coupled atmosphere-ocean-sea ice models struggle to capture the spatial and temporal characteristics of the Antarctic sea ice minimum. Education, outreach, and communication activities have supported the YOPP-SH SOP efforts. Based on the success of this Antarctic summer YOPP-SH SOP, a winter YOPP-SH SOP is being organized to support explorations of Antarctic atmospheric predictability in the austral cold season when the southern sea-ice cover is rapidly expanding. 

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