Eddy covariance flux observations at a semi-natural grassland on the Indo-Gangetic Plain

A new network of eddy covariance (EC) stations was established at a variety of semi-natural and managed ecosystems located across India during the INCOMPASS project. These new stations were installed to monitor surface-atmosphere fluxes of water, energy and carbon dioxide (CO2) and to provide supporting micrometeorological and soil physics observations. In this presentation, EC flux observations obtained at a semi-natural Phragmites-Saccharum-Imperata grassland on the Indo-Gangetic Plain are presented. The poster presents flux observations captured over two complete annual cycles. The grassland was characterised by a distinct seasonality. Latent heat dominated the turbulent energy flux during Monsoon, whereas sensible heat was the dominant turbulent flux during winter. The site experienced periodic flooding by waters from an adjacent irrigation canal as well as the removal of aboveground biomass during a wildfire in May 2017. Additional flood waters did not have a large influence on turbulent energy fluxes during inundation periods. Wildfire influenced fluxes in the period after the burn. Latent heat and net carbon gain recovered to pre-disturbance levels within a month of the wildfire

Monitoring dryland energy and water dynamics in India: an analysis of COSMOS-India and flux tower observations

Small changes in precipitation and temperature can dramatically influence surface energy and water budgets in semi-arid regions. Quantifying land-atmosphere interactions and feedbacks in these areas is crucial to understanding global water and carbon cycles, for the development and testing of land surface, weather prediction and climate models, as well as for monitoring local water resources and agricultural output. We report the results of co-located observations of land surface water and energy fluxes and large-area soil moisture dynamics obtained at three study sites located across India. These sites were instrumented as part of the INCOMPASS (INteraction of Convective Organisation with Monsoon Precipitation, Atmosphere, Surface and Sea) and COSMOS-India projects. Two sites are located on contrasting red (Alfisols) and black (Vertisols) soils on the Deccan Plateau. A third site is installed on alluvial soils (Fluvisols) on the Indo-Gangetic Plain. Each site consists of an eddy covariance flux tower providing measurements of sensible (H) and latent heat (LE) fluxes, micrometeorology and soil physics, in combination with a COSMOS (COsmic-ray Soil Moisture Observing System) sensor that provides spatially-integrated measurements of soil water content at field scale. In this presentation, we report on feedbacks between the land surface and the atmosphere, with a specific focus on the evaporative fraction (EF=LE/LE+H), precipitation and time varying soil moisture dynamics. CEH: Ross Morrison, Jonathan Evans, Chris Taylor, Lucy Ball, Alan Jenkins, Hollie Cooper, Jenna Thornton. IISc (Indian Institute of Science): Sekhar Muddu. University of Agricultural Sciences, Dharwad: S.S. Angadi. Indian Institute of Technology, Kanpur: Sachi Tripathi, Mithun Krishnan, Geet George. University of Reading: Andrew G. Turner

Cosmic-ray soil water monitoring: the development, status & potential of the COSMOS-India network

Soil moisture (SM) plays a central role in the hydrological cycle and surface energy balance and represents an important control on a range of land surface processes. Knowledge of the spatial and temporal dynamics of SM is important for applications ranging from numerical weather and climate predictions, the calibration and validation of remotely sensed data products, as well as water resources, flood and drought forecasting, agronomy and predictions of greenhouse gas fluxes. Since 2015, the Centre for Ecology and Ecology has been working in partnership with several Indian Research Institutes to develop COSMOS-India, a new network of SM monitoring stations that employ cosmic-ray soil moisture sensors (CRS) to deliver high temporal frequency, near-real time observations of SM at field scale. CRS provide continuous observations of near-surface (top 0.1 to 0.2 m) soil volumetric water content (VWC; m3 m-3) that are representative of a large footprint area (approximately 200 m in radius). To date, seven COSMOS-India sites have been installed and are operational at a range of locations that are characterised by differences in climate, soil type and land management. In this presentation, the development, current status and future potential of the COSMOS-India network will be discussed. Key results from the COSMOS-India network will be presented and analysed

Lipopolysaccharide Renders Transgenic Mice Expressing Human Serum Amyloid P Component Sensitive to Shiga Toxin 2

Transgenic C57BL/6 mice expressing human serum amyloid P component (HuSAP) are resistant to Shiga toxin 2 (Stx2) at dosages that are lethal in HuSAP-negative wild-type mice. However, it is well established that Stx2 initiates extra-intestinal complications such as the haemolytic-uremic syndrome despite the presence of HuSAP in human sera. We now demonstrate that co-administering purified Escherichia coli O55 lipopolysaccharide (LPS), at a dosage of 300 ng/g body weight, to HuSAP-transgenic mice increases their susceptibility to the lethal effects of Stx2. The enhanced susceptibility to Stx2 correlated with an increased expression of genes encoding the pro-inflammatory cytokine TNFα and chemokines of the CXC and CC families in the kidneys of LPS-treated mice, 48 hours after the Stx2/LPS challenge. Co-administering the glucocorticoid dexamethasone, but not the LPS neutralizing cationic peptide LL-37, protected LPS-sensitized HuSAP-transgenic mice from lethal doses of Stx2. Dexamethasone protection was specifically associated with decreased expression of the same inflammatory mediators (CXC and CC-type chemokines and TNFα) linked to enhanced susceptibility caused by LPS. The studies reveal further details about the complex cascade of host-related events that are initiated by Stx2 as well as establish a new animal model system in which to investigate strategies for diminishing serious Stx2-mediated complications in humans infected with enterohemorrhagic E. coli strains

Large-Eddy Simulations of Marine Boundary Layer Clouds Associated with Cold-Air Outbreaks during the ACTIVATE Campaign. Part I: Case Setup and Sensitivities to Large-Scale Forcings

ABSTRACT: Large-eddy simulation (LES) is able to capture key boundary layer (BL) turbulence and cloud processes. Yet, large-scale forcing and surface turbulent fluxes of sensible and latent heat are often poorly prescribed for LESs. We derive these quantities from measurements and reanalysis obtained for two cold-air outbreak (CAO) events during Phase I of the Aerosol Cloud Meteorology Interactions over the Western Atlantic Experiment (ACTIVATE) in February–March 2020. We study the two contrasting CAO cases by performing LES and test the sensitivity of BL structure and clouds to large-scale forcings and turbulent heat fluxes. Profiles of atmospheric state and large-scale divergence and surface turbulent heat fluxes obtained from ERA5 data agree reasonably well with those derived from ACTIVATE field measurements for both cases at the sampling time and location. Therefore, we adopt the time-evolving heat fluxes, wind, and advective tendencies profiles from ERA5 data to drive the LES. We find that large-scale thermodynamic advective tendencies and wind relaxations are important for the LES to capture the evolving observed BL meteorological states characterized by the hourly ERA5 data and validated by the observations. We show that the divergence (or vertical velocity) is important in regulating the BL growth driven by surface heat fluxes in LESs. The evolution of liquid water path is largely affected by the evolution of surface heat fluxes. The liquid water path simulated in LES agrees reasonably well with the ACTIVATE measurements. This study paves the path to investigate aerosol–cloud–meteorology interactions using LES informed and evaluated by ACTIVATE field measurements

Observed impact of meso-scale vertical motion on cloudiness

International audienceWe use estimates of mesoscale vertical velocity and collocated cloud measurements from the second Next-Generation Aircraft Remote Sensing for Validation campaign (NARVAL2) in the tropical North Atlantic to show the observed impact of mesoscale vertical motion on tropical clouds. Our results not only confirm previously untested hypotheses about the role of dynamics being nonnegligible in determining cloudiness, but go further to show that at the mesoscale, the dynamics has a more dominant control on cloudiness variability than thermodynamics. A simple massflux estimate reveals that mesoscale vertical velocity at the subcloud-layer top explains much of the variations in peak shallow cumulus cloud fraction. In contrast, we find that thermodynamic cloud-controlling factors, such as humidity and stability, are unable to explain the variations in cloudiness at the mesoscale. Thus, capturing the observed variability of cloudiness may require not only a consideration of thermodynamic factors, but also dynamic ones such as the mesoscale vertical velocity. SIGNIFICANCE STATEMENT: Knowing how low clouds link to atmospheric circulation over a few hundred kilometers will reduce current uncertainties in the sensitivity of Earth's climate to warming. Such investigations have previously been limited by lack of circulation measurements at the mesoscale. However, using measurements now available from a recent field campaign over the tropical North Atlantic along with cloud measurements, we demonstrate how atmospheric vertical motion especially in the lower layers can influence the extent and structure of clouds. We find that the kinematics have a more dominant control on low-level cloudiness than conventionally studied thermodynamics. Our results show why it is important to focus attention to the circulation to improve our understanding of the variability in cloudiness

Widespread shallow mesoscale circulations observed in the trades

International audienceUnderstanding the drivers of cloud organization is crucial for accurately estimating cloud feedbacks and their contribution to climate warming. Shallow mesoscale circulations are thought to play an important role in cloud organization, but they have not been observed. Here we present observational evidence for the existence of shallow mesoscale overturning circulations using divergence measurements made during the EUREC4A field campaign in the North Atlantic trades. Meteorological re-analyses reproduce the observed low-level divergence well and confirm the circulations to be mesoscale features (around 200 km across). We find that the shallow mesoscale circulations are associated with large variability in mesoscale vertical velocity and amplify moisture variance at the cloud base. Through their modulation of cloud-base moisture, the circulations influence how efficiently the subcloud layer dries, thus producing moist ascending branches and dry descending branches. The observed moisture variance differs from expectations from large-eddy simulations, which show the largest variance near the cloud top and negligible subcloud variance. The ubiquity of shallow mesoscale circulations, and their coupling to moisture and cloud fields, suggests that the strength and scale of mesoscale circulations are integral to determining how clouds respond to climate change

Strong cloud-circulation coupling explains weak trade cumulus feedback

International audienceShallow cumulus clouds in the trade-wind regions cool the planet by reflecting solar radiation. The response of trade cumulus clouds to climate change is a key uncertainty in climate projections1-4. Trade cumulus feedbacks in climate models are governed by changes in cloud fraction near cloud base5,6, with high-climate-sensitivity models suggesting a strong decrease in cloud-base cloudiness owing to increased lower-tropospheric mixing5-7. Here we show that new observations from the EUREC4A (Elucidating the role of cloud-circulation coupling in climate) field campaign8,9 refute this mixing-desiccation hypothesis. We find the dynamical increase of cloudiness through mixing to overwhelm the thermodynamic control through humidity. Because mesoscale motions and the entrainment rate contribute equally to variability in mixing but have opposing effects on humidity, mixing does not desiccate clouds. The magnitude, variability and coupling of mixing and cloudiness differ markedly among climate models and with the EUREC4A observations. Models with large trade cumulus feedbacks tend to exaggerate the dependence of cloudiness on relative humidity as opposed to mixing and also exaggerate variability in cloudiness. Our observational analyses render models with large positive feedbacks implausible and both support and explain at the process scale a weak trade cumulus feedback. Our findings thus refute an important line of evidence for a high climate sensitivity10,11

Strong cloud-circulation coupling explains weak trade cumulus feedback

International audienceShallow cumulus clouds in the trade-wind regions cool the planet by reflecting solar radiation. The response of trade cumulus clouds to climate change is a key uncertainty in climate projections1-4. Trade cumulus feedbacks in climate models are governed by changes in cloud fraction near cloud base5,6, with high-climate-sensitivity models suggesting a strong decrease in cloud-base cloudiness owing to increased lower-tropospheric mixing5-7. Here we show that new observations from the EUREC4A (Elucidating the role of cloud-circulation coupling in climate) field campaign8,9 refute this mixing-desiccation hypothesis. We find the dynamical increase of cloudiness through mixing to overwhelm the thermodynamic control through humidity. Because mesoscale motions and the entrainment rate contribute equally to variability in mixing but have opposing effects on humidity, mixing does not desiccate clouds. The magnitude, variability and coupling of mixing and cloudiness differ markedly among climate models and with the EUREC4A observations. Models with large trade cumulus feedbacks tend to exaggerate the dependence of cloudiness on relative humidity as opposed to mixing and also exaggerate variability in cloudiness. Our observational analyses render models with large positive feedbacks implausible and both support and explain at the process scale a weak trade cumulus feedback. Our findings thus refute an important line of evidence for a high climate sensitivity10,11

Mass flux estimates and their relationship to cloud-base cloudiness during the EUREC4A campaign

International audienceThe trade-cumulus cloud feedback in climate models is mostly driven by changes in cloud-base cloudiness, which can largely be attributed to model differences in the strength of lower-tropospheric mixing. Using observations from the recent EUREC<sup>4</sup>A field campaign, we test the hypothesis that enhanced lower-tropospheric mixing dries the lower cloud layer and reduces near-base cloudiness. The convective mass flux at cloud base is used as a proxy for the strength of convective mixing and is estimated as the residual of the subcloud layer mass budget, which is derived from dropsondes intensively launched along a circle of ~200 km diameter. The cloud-base cloud fraction is measured with horizontally-pointing lidar and radar from an aircraft flying near cloud base within the circle area. Additional airborne, ground- and ship-based radar, lidar and in-situ measurements are used to estimate the total cloud cover, the surface fluxes and to validate the consistency of the approach.</p><p>Preliminary mass flux estimates have reasonable mean values of about 15 mm/s. 3- circle (i.e. 3h) averaged estimates range between 0-40 mm/s and reveal substantial day-to-day and daily variability. The day-to-day variability in the mass flux is mostly due to variability in the mesoscale vertical velocity, whereas the entrainment rate mostly explains variability on the daily timescale, consistent with previous large-eddy simulations. We find the mass flux to be positively correlated to both the cloud-base cloud fraction and the total cloud cover (R=0.55 and R~0.4, respectively). Other indicators of lower-tropospheric mixing due to convection and mesoscale circulations also suggest positive relationships between mixing and cloudiness. Implications of these analyses for testing the hypothesized mechanism of positive trade-cumulus cloud feedback will be discussed.</p&gt