ALBERT

Description: The goal of the Sea2Cloud project is to study the interplay between surface ocean biogeochemical and physical properties, fluxes to the atmosphere and ultimately their impact on cloud formation under minimal direct anthropogenic influence. Here we present an interdisciplinary approach, combining atmospheric physics and chemistry with marine biogeochemistry, during a voyage between 41 and 47°S in March 2020. In parallel to ambient measurements of atmospheric composition and seawater biogeochemical properties, we describe semi-controlled experiments to characterize nascent sea spray properties and nucleation from gas-phase biogenic emissions. The experimental framework for studying the impact of the predicted evolution of ozone concentration in the Southern Hemisphere is also detailed. After describing the experimental strategy, we present the oceanic and meteorological context including provisional results on atmospheric thermodynamics, composition, and flux measurements. In situ measurements and flux studies were carried out on different biological communities by sampling surface seawater from subantarctic, subtropical and frontal water masses. Air-Sea-Tanks (ASIT) were used to quantify biogenic emissions of trace gases under realistic environmental conditions, with nucleation observed in association with biogenic seawater emissions. Sea spray continuously generated produced sea spray fluxes of 34% of organic matter by mass, of which 4% particles had fluorescent properties, and which size distribution ressembled the one found in clean sectors of the Southern Ocean. The goal of Sea2Cloud is to generate realistic parameterizations of emission flux dependences of trace gases and nucleation precursors, sea spray, cloud condensation nuclei and ice nuclei using seawater biogeochemistry, for implementation in regional atmospheric models.

Description: THINICE is an international airborne field campaign that occurred in Svalbard in August 2022 co-organized by French, British and US colleagues. It was dedicated to studying the dynamics of Arctic cyclones (ACs), moist intrusions, tropopause polar vortices (TPVs), their interactions with cloud microphysics, sea surface and sea ice. Two instrumented research aircraft were deployed: the ATR42 aircraft operated by SAFIRE, the French facility for airborne research, and the Twin Otter aircraft operated by the British Antarctic Survey (BAS). The objectives of the ATR42 flights were to observe the structure and evolution of Arctic cyclones over the whole tropospheric column with a focus on mixed phase clouds within Arctic cyclones. The objectives of the Twin Otter flights were more on boundary-layer processes by measuring turbulent fluxes, surface heat fluxes and sea-ice surface elevation. After providing an overview of the field campaign, the presentation will focus on ATR42 flights that crossed warm fronts within Arctic cyclones and during which mixed-phase clouds have been intensively observed. We will show how the measurements made by in-situ cloud microphysical probes and the remote-sensing platform RALI composed of the Doppler radar RASTA and the lidar LNG on board the ATR42 aircraft have been combined to get a comprehensive picture of mixed-phase clouds properties.

Description: The main scientific objective of the EXAEDRE (EXploiting new Atmospheric Electricity Data for Research and the Environment) project focused on the observational- and modeling-based characterization of the thunderstorms in the Corsica region in the Northwestern Mediterranean Sea. A dedicated airborne campaign was conducted between 13 September 2018 and 08 October 2018 using the French Falcon research aircraft equipped with an instrumental package composed of 8 electric field mills AMPERA, a series of microphysics probes PMA and the vertical pointing cloud Doppler radar RASTA. The SAETTA VHF Lightning Mapping Array (LMA) and the Météorage VLF network recorded the total lightning activity of the sampled electrical cells. Eight different weather situations have been documented with different convection features and sampled at close and distant ranges of the lightning activity. An overview of those eight flights will be presented with an emphasis on the strength of the measured electric field (up to 79 kV/m) according to the parent cloud structure as documented by the airborne cloud radar and the operational weather radars, the nature of the microphysics measured at the flight altitude and the charge layer structure as deduced from the LMA observations.

Description: Extra-tropical cyclones transiting into the Arctic are of great importance for the heat and moisture budgets of the polar atmosphere and strongly modulate the sea ice variability. Arctic cyclones are also systems that lead to the formation of clouds, and in particular mixed-phase clouds, whose amount of supercooled liquid water strongly determine the radiative effect thereof. Correctly representing those clouds in atmospheric models is crucial to properly simulate precipitations and the surface energy budget in a region warming twice as fast as the rest of the globe. In August 2022, the Rali-Thinice campaign took place in Svalbard and aimed to characterize the dynamical and microphysical structure of Arctic cyclones. A research aircraft equipped with measurement systems such as two radars, a lidar and microphysical probes flew over the Arctic Ocean sampling several cases of summer cyclones. The data acquired during this campaign are extremely valuable to carry out an in-depth evaluation of the ability of atmospheric models to simulate Arctic cyclones and their associated clouds. LMDZ is the global atmospheric component of the IPSL-CM Earth System Model, actively and historically involved in the CMIP exercises. The new DYNAMICO-LMDZ configuration which consists of the physics of LMDZ coupled to the recent icosahedral dynamical core DYNAMICO is run in a new regional configuration on a domain surrounding the Svalbard archipelago. The representation of the dynamics and thermodynamics of cyclones as well as cloud properties is assessed using the set of measurements acquired during Rali-Thinice campaign complemented with surface station data and radiosondes.

Description: Mixed-phase clouds are common in Arctic cyclones, but their representation in global atmospheric models is still challenging. The aim of the study is to evaluate and improve the ratio of ice and liquid water within mixed-phase clouds simulated by two general circulation models (GCM): ARPEGE (operational at Météo-France) and LMDZ (the atmospheric component of the IPSL-CM Earth System Model). For that evaluation, we consider ERA5 reanalysis for the overall dynamics and for the cloud representation, DARDAR satellite products which provide the ice water content (IWC) as well as categorization masks along CloudSat-CALIPSO tracks. This work focuses on an Arctic cyclone that occurred in May 2019 near Svalbard and has been sampled several times by CloudSat-CALIPSO. Compared to satellite observations, LMDZ simulations provide quite realistic IWC while ARPEGE underestimates this quantity. However, by comparing liquid and ice occurrences between models and observations, both GCMs clearly miss occurrences of liquid phase at temperature lower than -30°C but they all overestimate the liquid occurrence in the whole negative temperature range between 0°C and -30°C. In order to improve such liquid and ice occurrences, different liquid/ice partition functions are tested in the two models. In particular, different shapes and extensions to lower temperatures are considered. This helps to improve the occurrence of liquid water at the lowest temperatures but does not correct the overestimation between 0°C and -30°C. As temperature does not discriminate liquid-ice partition properly, different other predictors are tested and distance from the cloud top appears to be the most relevant.