Algorithm for Improved Stereoscopic Cloud-Top Height Retrieval Based on Visible and Infrared Bands for Himawari-8 and FY-4A

Stereoscopic cloud-top height (CTH) retrieval from two geostationary (GEO) satellites is usually realized through a visible (VIS) band with a high horizontal resolution. A stereoscopic-based CTH retrieval algorithm (prototype dual-GEO CTH algorithm) proposed in our previous study also adopts this approach. Although this approach can retrieve accurate stereoscopic CTHs, the heights of optically thin upper clouds overlying the lower clouds are challenging to retrieve because the parallax difference between two GEOs is determined by the lower clouds owing to the low reflectance from the upper clouds. To address this problem, this paper proposes an improved stereoscopic CTH retrieval algorithm, named the improved dual-GEO CTH algorithm, for Himawari-8 and FengYun (FY)-4A GEOs. The proposed algorithm employs an infrared (IR) band in addition to a VIS band. A seamless image cloning technique is adopted to blend the VIS and IR images, which are then used to retrieve the stereoscopic CTHs. The retrieved CTHs are compared with the Cloud-Aerosol Lidar with Orthogonal Polarization (CALIOP) and Cloud Profiling Radar (CPR) CTHs for three occasions involving upper clouds overlying lower clouds. Results show that the proposed algorithm outperforms the prototype dual-GEO CTH algorithm in the case of upper clouds overlying lower clouds. Notably, although the proposed algorithm is intended for Himawari-8 and FY-4A GEOs, it can be easily extended to any combination of two GEOs.

Deep Eastern Boundary Currents: idealized models and dynamics

Concentrated poleward flows along eastern boundaries between two and four kilometers depth in the southeast Pacific, Atlantic, and Indian Oceans have been observed, and appear in data-assimilation products and regional model simulations at sufficiently high horizontal resolution, but their dynamics are still not well understood. We study the local dynamics of these Deep Eastern Boundary Currents (DEBCs) using idealized GCM simulations and use a conceptual vorticity model for the DEBCs, to gain additional insights into the dynamics. Over most of the zonal width of the DEBCs, the vorticity balance is between meridional advection of planetary vorticity and vortex stretching, which is an interior-like vorticity balance. Over a thinner layer very close to the eastern boundary, a balance between vorticity tendencies due to friction and stretching that rapidly decay away from the boundary is found. Over the part of the DEBC that is governed by an interior-like vorticity balance, vertical stretching is driven by both the topography and temperature diffusion, while in the thinner boundary layer, it is driven instead by parameterized horizontal temperature mixing. The topographic driving acts via a cross-isobath flow that leads to stretching and thus to vorticity forcing for the concentrated DEBCs.

Reforecast of the November 1994 flood in Piedmont using ERA5 and COSMO model: an operational point of view

The scope of this work is to assess the progresses made in the warning alert system of Piedmont since the 1994 flood. We used the COSMO model at high horizontal resolution forced by ERA5 re-forecast to simulate the November 1994 event, performing also a simple sensitivity test regarding the parameterization of convection. We compared the results with the original forecast and with the available observations, in order to understand how the emission of the alert would have been affected using the current operational system.

A new TROPOMI product for tropospheric NO₂ columns over East Asia with explicit aerosol corrections

We present a new product with explicit aerosol corrections, POMINO-TROPOMI, for tropospheric nitrogen dioxide (NO2) vertical column densities (VCDs) over East Asia, based on the newly launched TROPOspheric Monitoring Instrument with an unprecedented high horizontal resolution. Compared to the official TM5-MP-DOMINO (OFFLINE) product, POMINO-TROPOMI shows stronger concentration gradients near emission source locations and better agrees with MAX-DOAS measurements (R2=0.75; NMB=0.8 % versus R2=0.68, NMB=-41.9 %). Sensitivity tests suggest that implicit aerosol corrections, as in TM5-MP-DOMINO, lead to underestimations of NO2 columns by about 25 % over the polluted northern East China region. Reducing the horizontal resolution of a priori NO2 profiles would underestimate the retrieved NO2 columns over isolated city clusters in western China by 35 % but with overestimates of more than 50 % over many offshore coastal areas. The effect of a priori NO2 profiles is more important under calm conditions.

Atmospheric methane monitoring and analysis using tropOMI retrievals at ECMWF.

<p>The European Union’s Copernicus Atmosphere Monitoring Service (CAMS) operationally provides daily forecasts of global atmospheric composition. It uses the ECMWF Integrated Forecasting System (IFS), which includes meteorological and atmospheric composition variables, such as reactive gases, greenhouse gases and aerosols, for its global forecasts and reanalyses. The current green-house gases operational suite monitors CH4 and CO2 and assimilates TANSO and IASI retrievals for both species. The TROPOspheric Monitoring Instrument (TROPOMI) on board the Sentinel-5 Precursor (S5P) satellite launched in October 2017 yields a wealth of atmospheric composition data, including CH<sub>4</sub> retrievals at unprecedented high horizontal resolution (7km) and up to daily revisit time. We used the IFS to perform monitoring experiments at different horizontal resolutions (25 km and 9 km). We also performed first data assimilation experiments at 25 km horizontal resolution.</p><p>This first set of monitoring experiments shows the potential of the TROPOMI CH<sub>4</sub> retrievals to correct known biases that exist in the current CAMS analyses and forecasts. Assimilation experiments of TROPOMI CH<sub>4</sub> shows that adding the instrument in the operational chain would significantly improve the analysis and forecasts. Detection of CH<sub>4</sub> sources seen by TROPOMI compared to CAMS also shows the potential of the instrument to inform on and infer anthropogenic and natural sources. For example, discrepancies between TROPOMI retrievals and CAMS fields in the CH<sub>4</sub> levels associated with oil and gas extraction activities show very promising perspectives for monitoring and analysis of CH<sub>4</sub> concentration and emissions. We will finally discuss the challenges and progress made towards performing inversions using the IFS operational system.  </p>

A new TROPOMI product for tropospheric NO₂ columns over East Asia with explicit aerosol corrections

We present a new product with explicit aerosol corrections, POMINO-TROPOMI, for tropospheric nitrogen dioxide (NO2) vertical column densities (VCDs) over East Asia, based on the newly launched TROPOspheric Monitoring Instrument with an unprecedented high horizontal resolution. Compared to the official TM5-MP-DOMINO (OFFLINE) product, POMINO-TROPOMI shows stronger concentration gradients near emission source locations and better agrees with MAX-DOAS measurements (R2 = 0.75, NMB = 0.8 % versus R2 = 0.68, NMB = 41.9 %). Sensitivity tests suggest that implicit aerosol corrections, as in TM5-MP-DOMINO, lead to underestimations of NO2 columns by about 25 % over the polluted Northern East China region. Reducing the horizontal resolution of a priori NO2 profiles would underestimate the retrieved NO2 columns over isolated city clusters in western China by 35 % but with overestimates by more than 50 % over many offshore coastal areas. The effect of a priori NO2 profiles is more important under calm conditions.

Rotation of floating particles in submesoscale cyclonic and anticyclonic eddies: a model study for the southeastern Baltic Sea

We hypothesized that the overwhelming dominance of cyclonic spirals on satellite images of the sea surface could be caused by some differences between the rotary characteristics of submesoscale cyclonic and anticyclonic eddies. This hypothesis was tested by means of numerical experiments with synthetic floating Lagrangian particles embedded offline in a regional circulation model of the southeastern Baltic Sea with very high horizontal resolution (0.125 nautical mile grid). The numerical experiments showed that the cyclonic spirals can be formed from both a horizontally uniform initial distribution of floating particles and from the initially lined-up particles during an advection time of the order of 1 d. Statistical processing of the trajectories of the synthetic floating particles allowed us to conclude that the submesoscale cyclonic eddies differ from the anticyclonic eddies in three ways favoring the formation of spirals in the tracer field: they can be characterized by (a) a considerably higher angular velocity, (b) a more pronounced differential rotation and (c) a negative helicity.

Rotation of floating particles in submesoscale cyclonic and anticyclonic eddies: a model study for the southeastern Baltic Sea

It was assumed that the overwhelming dominance of cyclonic spirals on satellite images of the sea surface could be caused by some sort of differences between rotary characteristics of the submesoscale cyclonic and anticyclonic eddies. This hypothesis was tested by means of numerical experiments with synthetic floating Lagrangian particles embedded in a regional circulation model of the southeastern Baltic Sea with very high horizontal resolution (0.125 nautical mile grid). The numerical experiments showed that the cyclonic spirals can be formed both from a horizontally uniform initial distribution of floating particles and from the initially lined up particles during the advection time of the order of 1 day. Statistical processing of the trajectories of the synthetic floating particles allowed to conclude that the submesoscale cyclonic eddies differ from the anticyclonic eddies in three ways favouring the formation of the spirals: the former can be characterized by a considerably higher angular velocity and a more pronounced differential rotation as well as by a negative helicity.

The climate change signal in the Mediterranean Sea in a regionally coupled ocean-atmosphere model

We assess the role of ocean feedbacks in the simulation of the present climate and on the downscaled climate change signal in the Mediterranean Sea with the regionally coupled model REMO-OASIS-MPIOM (ROM). The ROM oceanic component is global with regionally high horizontal resolution in the Mediterranean Sea. In our setup the Atlantic and Black Sea circulations are simulated explicitly. Simulations forced by ERA-Interim show a good representation of the present Mediterranean climate. Our analysis of the RCP8.5 scenario driven by MPI-ESM shows that the Mediterranean waters will be warmer and saltier across most of the basin by the end of the century. In the upper ocean layer temperature is projected to have a mean increase of 2.73 °C, while the mean salinity increases by 0.17 psu, presenting a decreasing trend in the Western Mediterranean, opposite to the rest of the basin. The warming initially takes place at the surface and propagates gradually to the deeper layers.