Studio della convezione durante il monsone africano: osservazioni e modellazione della precipitazione e del ruolo della circolazione regionale sulla composizione atmosferica

The improvement of knowledge and understanding of the West African Monsoon (WAM) is a fundamental scientific issue with implications on economy, health, water resources and food security in West African countries. In a region where agriculture is mainly rain fed, a delay in the rainy season onset or a dry year could compromise food and water security and lead to dearth conditions. The natural interannual and interseasonal variability of the WAM and the dramatic change from wet conditions (1950s-1960s) to much drier ones (1960s-today) over West Africa represents one of the world strongest variation in the 20th century. Mesoscale convective systems (MCS) are responsible for the 80% of the rain production in the sub- Saharan region during the rainy season (June-September), playing a key role in the rainfall variability over a large domain of spatial and temporal scales. The annual variability of MCSs in West Africa is driven by monsoon circulation, which provides favourable conditions for convection formation in the Sahelian area. An increase in the vulnerability of West African societies to climate variability is expected for the next decades as demands on resources increase in association with growing population and for those reasons predictions at various scales of the WAM is a key issue for West African countries. Further motivation comes from the need to quantify the role of the WAM on the global climate. Africa is one of the largest and less known sources of dust and aerosols, which plays a major role in radiative forcing and in cloud microphysics. Furthermore Africa emits the largest amount of biomass burning emissions with a strong interhemispheric transition between West Africa in boreal winter to Central and Southern Africa in boreal summer following the location of the dry season in each hemisphere. Moreover emissions due to urban pollution of large African cities are poorly known due to a lack of in-situ measurements. Satellite observations indicates that large areas in West Africa appear to be characterized by industrial activity, traffic, biomass burning from house fires that can have a great impact on air quality and possibly damage vegetation growth and agricultural production. In this work we have approached three issues: (1) how mesoscale models describe the dynamics of MCS (2) how to improve them in order to improve water cycle, precipitation and deep convection analysis and (3) which dynamical mechanisms drive the chemical composition of the atmosphere in Africa Firstly, the ability of the mesoscale meteorological model BOLAM (BOlogna Limited Area Model) in reproducing convection in West Africa has been tested against other meteorological models and rainfall measurements. Models performed simulations of the propagation of a MCS observed to cross part of West Africa in August 2005. An evaluation of precipitation simulated by mesoscale models is carried out. It has been found that the BOLAM model is capable to reproduce the structure and the associated precipitation of the observed squall line even if it overestimates precipitation amount with respect to the reference satellite estimations and produces a eastward shifted rain band. The models intercomparison showed that convective precipitation forecast in West Africa is a difficult issue to be addressed. To address this issue we have developed and implemented into the BOLAM model a nudging scheme based on the use of satellite observations of cloud top brightness temperature to correct the model humidity profiles. The nudging approach is based on the continuous assimilation of METEOSAT infrared brightness temperatures within the model in order to trigger convection, where observations show the presence of large convective systems. The nudging also inhibits convection, when the model reproduces unrealistic convective precipitation and coherently modifies the dynamical fields. It is shown that the assimilation scheme improves the geographical distribution and time evolution of the MCSs reproduced by the model; the impact of assimilation is positive up to 13 hours after the end of the nudging period. It is also shown that the nudging improves the simulated amount and spatial distribution of precipitation. In order to upscale the results obtained on a single event, we performed a seasonal mesoscale simulation covering west Africa during the whole monsoon season. Therein the nudging scheme is used throughout the period to obtain a reanalysis for the June-August 2006 period. The assimilation of cloud top brightness temperature greatly improves the spatial patterns and the amount of rainfall generated by the BOLAM model over a seasonal time-scale. The last issue studied in the present work regards the transport of pollutants and greenhouse gases in the African continent. We used BOLAM mesoscale model simulations, nudged with infrared radiance temperature, to estimate the convective impact in the upper troposphere and to assess the fraction of air processed by convection. Comparison between simulated convective transport and aircraft measurements shows that BOLAM model correctly reproduces the location and the vertical structure of convective outflow. Model-aided analysis indicates that convection can influence the composition of the upper troposphere above the level of main outflow for an event of deep convection close to the observation site and that deep convection occurring in the central Sahelian region has a likely role in convective transport in the upper troposphere. Then we focused on the long-range transport of biomass burning gases out of West Africa, which has been recognised to have important implications for the global oxidizing capacity of the atmosphere and global climate change. Mid and upper-tropospheric pollutant plumes with enhanced levels of trace gases and aerosols were observed over the southern coast of West Africa during August 2006 as part of the AMMA wet season field campaign. Runs using the BOLAM mesoscale model including biomass burning CO tracers were used to confirm an origin from central African fires. Modelled tracer results showed that pollutants resided for between 9 and 12 days over Central Africa before being transported for 4 days, in the case of the mid-troposphere plume, and 2 days in the case of the upper tropospheric plume to the measurement location over the southern part of West Africa

Impact of deep convection in the tropical tropopause layer in West Africa: in-situ observations and mesoscale modelling

We present the analysis of the impact of convection on the composition of the tropical tropopause layer region (TTL) in West-Africa during the AMMA-SCOUT campaign. Geophysica M55 aircraft observations of water vapor, ozone, aerosol and CO2 show perturbed values at altitudes ranging from 14 km to 17 km (above the main convective outflow) and satellite data indicates that air detrainment is likely originated from convective cloud east of the flight. Simulations of the BOLAM mesoscale model, nudged with infrared radiance temperatures, are used to estimate the convective impact in the upper troposphere and to assess the fraction of air processed by convection. The analysis shows that BOLAM correctly reproduces the location and the vertical structure of convective outflow. Model-aided analysis indicates that in the outflow of a large convective system, deep convection can largely modify chemical composition and aerosol distribution up to the tropical tropopause. Model analysis also shows that, on average, deep convection occurring in the entire Sahelian transect (up to 2000 km E of the measurement area) has a non negligible role in determining TTL composition

Early onset Mirror Syndrome associated with foetal sacrococcigeal teratoma: a rare entity

In the mirror syndrome, maternal symptoms mime foetal and placental oedema. The pathogenesis is unknown. The most common etiologic associations are rhesus isoimmunization, twin-twin transfusion syndrome and viral infections. Few reports are associated to foetal tumors and particularly to sacroccoccigeal teratoma (SCT). Based on several published series, foetal SCT with placentomegaly and hydrops is almost universally fatal; foetal surgery is not typically offered for hydropic foetuses beyond 26 weeks of gestational age. Delivery of the foetus is the choise treatment when mirror syndrome is present with supporting the pregnancy until delivery is necessary for maternal indications or the foetus is 30 weeks old. The management of a patient with large foetal sacrococcygeal teratoma, hydrops foetalis and early onset mirror syndrome is presented

Atmospheric temperature, water vapour and liquid water path from two microwave radiometers during MOSAiC

The microwave radiometers HATPRO (Humidity and Temperature Profiler) and MiRAC-P (Microwave Radiometer for Arctic Clouds - Passive) continuously measured radiation emitted from the atmosphere throughout the Multidisciplinary drifting Observatory for the Study of the Arctic Climate (MOSAiC) expedition on board the research vessel Polarstern. From the measured brightness temperatures, we have retrieved atmospheric variables using statistical methods in a temporal resolution of 1 s covering October 2019 to October 2020. The integrated water vapour (IWV) is derived individually from both radiometers. In addition, we present the liquid water path (LWP), temperature and absolute humidity profiles from HATPRO. To prove the quality and to estimate uncertainty, the data sets are compared to radiosonde measurements from Polarstern. The comparison shows an extremely good agreement for IWV, with standard deviations of 0.08–0.19 kg m−2 (0.39–1.47 kg m−2) in dry (moist) situations. The derived profiles of temperature and humidity denote uncertainties of 0.7–1.8 K and 0.6–0.45 gm−3 in 0–2 km altitude

Evaluating the quality of patient-specific deformable image registration in adaptive radiotherapy using a digitally enhanced head and neck phantom

This paper presents a deformable image registration-based method for the quality assurance of head and neck adaptive radiotherapy using digitally post-processed anthropomorphic phantom image datasets. One of the main findings of this work is that spatial and dose errors are a function of the magnitude of the deformation and of the gradient of the dose distribution. This emphasizes the importance of performing patient-specific deformable image registration verification and, consequently, the need to develop and make available tools that are for this purpose

Integrated water vapour derived from the MiRAC-P microwave radiometer onboard the Polarstern during the MOSAiC expedition

The data set contains daily files of path integrated amount of water vapour (precipitable water, prw) derived from the MiRAC-P (or LHUMPRO-243-340) microwave radiometer (see Mech et al., 2019) onboard the Polarstern during cruise PS122 (MOSAiC expedition). The data covers the range October 2019 to October 2020. MiRAC-P measures atmospheric radiation in six double side band averaged G band (183.31 +/- 0.6 to 183.31 +/- 7.5 GHz) and two higher frequency (243 and 340 GHz) channels. The different sensitivity to humidity of the channels allow a derivation of the path integrated amount of water vapour (prw). A Neural Network retrieval has been used to derive prw. The uncertainty of prw is given as the variable's comment attribute and describes the expected standard error. Prw is provided for all available times so that it is up to the user to decide whether or not to use the values if quality flags are set

Airborne remote sensing of cloud properties with the German research aircraft HALO

The new German research aircraft HALO (High Altitude Long range) can be equipped with a remote sensing payload to study cloud properties and water vapor profiles of the atmosphere. This package, first flown during the NARVAL (Next‐generation Aircraft Remote sensing for VALidation studies) mission in December 2013 and January 2014, consists of a cloud radar, microwave radiometers and a lidar system. HALO is a for atmospheric measurements modified Gulfstream G550 business jet with a maximum payload of about 3 tons, an endurance of more than 10 hours and a maximum ceiling of about 15 km. The HALO microwave package (HAMP) consists of the cloud radar and the microwave radiometers. The cloud radar is a nadir pointing Ka‐band radar (35 GHz) adapted from the METEX Mira‐36 radar. While the radar electronics resides in the cabin of the aircraft, the 1 m diameter antenna (0.6° beam width) is mounted inside the belly pod beneath the fuselage. The microwave radar radiometers build by Radiometer Physics (RPG) are operating at 26 frequencies in the K‐band (22 GHz, water‐vapor line), V‐band (58 GHz, O2 line), W‐band (90 GHz, window channel), F‐band (118 GHz, O2 line), and G‐band (183 GHz, water‐vapor line). The radiometers are mounted inside the belly‐pod in three containers with five nadir pointing antennas (beam width 2.7 to 5°). The lidar is the DLR WALES system with a water‐vapor DIAL (935 nm) and a HSRL (1064 and 532 nm) for cloud and aerosol properties. The focus of the NARVAL campaign was on the characterization of precipitation from shallow clouds in the North Atlantic trade wind zone (NARVAL‐South, December 2013) and on post‐frontal mesoscale precipitation systems over the North Atlantic near Iceland and Greenland (NARVAL‐North, January 2014). For intercomparison, additionally several patterns over ground stations like Jülich, Lindenberg, Leipzig, Mace‐Head, and Chilbolton were flown. Also a number of under‐passes of Cloudsat and Calipso were performed. A joint flight was also together with the French Falcon operating the 95 GHz cloud radar

Microwave Passive Ground-Based Retrievals of Cloud and Rain Liquid Water Path in Drizzling Clouds: Challenges and Possibilities

Satellite and ground-based microwave radiometers are routinely used for the retrieval of liquid water path (LWP) under all atmospheric conditions. The retrieval of water vapor and LWP from ground-based radiometers during rain has proved to be a difficult challenge for two principal reasons: the inadequacy of the nonscattering approximation in precipitating clouds and the deposition of rain drops on the instrument's radome. In this paper, we combine model computations and real ground-based, zenith-viewing passive microwave radiometer brightness temperature measurements to investigate how total, cloud, and rain LWP retrievals are affected by assumptions on the cloud drop size distribution (DSD) and under which conditions a nonscattering approximation can be considered reasonably accurate. Results show that until the drop effective diameter is larger than similar to 200 mu m, a nonscattering approximation yields results that are still accurate at frequencies less than 90 GHz. For larger drop sizes, it is shown that higher microwave frequencies contain useful information that can be used to separate cloud and rain LWP provided that the vertical distribution of hydrometeors, as well as the DSD, is reasonably known. The choice of the DSD parameters becomes important to ensure retrievals that are consistent with the measurements. A physical retrieval is tested on a synthetic data set and is then used to retrieve total, cloud, and rain LWP from radiometric measurements during two drizzling cases at the atmospheric radiation measurement Eastern North Atlantic site