Influence of the representation of convection on the mid-Holocene West African Monsoon

The focus of this dissertation is whether and how explicitly resolved convection simulations, compared to parameterized convection simulations, modify the West African monsoon and the precipitation distribution over mid-Holocene North Africa. Previous models could not reproduce the northern extent of the West African monsoon during the mid-Holocene because they used a too coarse horizontal resolution and therefore had to parameterize convective processes. For present-day conditions, Marsham et al. (2013) show that explicitly resolved convection shifts monsoonal precipitation much farther north and is able to better represent several key characteristics of precipitation compared to observations and compared to parameterized convection. Motivated by the results of Marsham et al. (2013), in the first part of this disser- tation I investigate whether the use of explicitly resolved convection simulations shifts the monsoonal precipitation further north than parameterized convection simulations during the mid-Holocene. Unexpectedly, I find that the northern extent of monsoonal precipitation remains further south when convection is resolved. I argue that the absence of a northward shift is caused mainly by fundamentally different precipitation characteristics, and by the response of surface hydrology to them when convection is explicitly resolved. As a result, precipitation in parameter- ized convection simulations is generally higher and extends further north than in explicitly resolved convection simulations. This result demonstrates the importance of soil moisture and surface conditions in regulating precipitation in mid-Holocene North Africa. Therefore, the second part of the thesis focuses on how land surface and soil moisture modify precipitation over North Africa in simulations with parameterized and explicitly resolved convection. For this purpose, I extend the simulations from the first part, which uses present-day land surface conditions, and prescribe a higher, idealized vegetation gradient over mid-Holocene North Africa that is closer to proxy data. First, prescribing a higher vegetation density over North Africa induces a posi- tive land-atmosphere feedback with enhanced precipitation and a further northward extent of monsoonal precipitation, regardless of the representation of convection. However, parameterized convection leads to stronger land-atmosphere feedback and thus higher sensitivity of precipitation to land surface changes compared to explicitly resolved convection. I hypothesize that this greater sensitivity is due to the generally higher soil moisture in the simulations with parameterized convection, which results from more but less intense precipitation and lower runoff - a similar mechanism as in part 1. In contrast, increased runoff prevents the formation of a strong soil moisture-precipitation feedback in simulation with explicitly resolved convection. Based on these results, I emphasize that it is critical how the soil re- sponds to precipitation, not just how precipitation is affected by soil moisture. The importance of soil hydrology to the strength of land-atmosphere coupling in models has not yet been considered. To test the hypothesis, I run another set of simulations for explicit and param- eterized convection with high vegetation density but with the same constant soil moisture field. The results show that for the same land surface conditions, monsoonal precipitation extends as far north with explicit convection as with parameterized convection. However, precipitation rates are still higher near the Guinea coast and over most of the Sahel in simulations with parameterized convection. Nevertheless, these results show a strong influence of soil moisture on the West African mon- soon and highlight the importance of a reliable representation of soil hydrology in models

How does the explicit treatment of convection alter the precipitation–soil hydrology interaction in the mid-Holocene African humid period?

Global climate models with coarse horizontal resolution are largely unable to reproduce the monsoonal precipitation pattern over North Africa during the mid-Holocene. Here we present the first regional, storm-resolving simulations with an idealized but reasonable mid-Holocene vegetation cover. In these simulations, the West African monsoon expands farther north by about 4–5∘, and the precipitation gradient between the Guinea coast and the Sahara decreases compared to simulations with a barren Sahara as it is today. The northward shift of monsoonal precipitation is caused by land surface–atmosphere interaction, i.e., the coupling of soil moisture and precipitation, as well as interactions of the land surface with the large-scale monsoon circulation (e.g., the African easterly jet). The response of the monsoon circulation to an increased vegetation cover is qualitatively similar but more pronounced in parameterized convection simulations. We attribute the differences in monsoonal precipitation to differences in soil moisture that are strongly controlled by runoff and precipitation characteristics. If precipitation is intense and falls over a spatially small region, as in our storm-resolving simulations, about 35 % of all precipitation water goes into runoff instead of filling soil moisture storage. In contrast, in light and spatially more homogeneous precipitation, as produced in our parameterized convection simulations, only some 20 % leaves the grid cell as runoff. Therefore, much more water is available to maintain high soil moisture content. We confirm the significant role of soil moisture and runoff by performing simulations with the same constant soil moisture field in both storm-resolving and parameterized convection simulations. These constant soil moisture simulations cancel the effect of lower soil moisture on the land–atmosphere feedback cycle in our storm-resolving simulations. We show that precipitation strongly increases in the storm-resolving simulations, especially in moisture-controlled regions, such as the northern Sahel and Sahara, and reaches equally high values as in parameterized convection simulations. Our study highlights how the type of rainfall (e.g., local and intense or widespread and light) impacts soil moisture and thus land–atmosphere feedbacks. This is contrary to many studies that focus mainly on the amount of rainfall and how it modifies land–atmosphere feedbacks. Moreover, this study suggests that comprehensive land-surface schemes, which appropriately respond to varying precipitation characteristics, are needed for studying land surface–atmosphere interaction.</p

The management of acute venous thromboembolism in clinical practice. Results from the European PREFER in VTE Registry

Venous thromboembolism (VTE) is a significant cause of morbidity and mortality in Europe. Data from real-world registries are necessary, as clinical trials do not represent the full spectrum of VTE patients seen in clinical practice. We aimed to document the epidemiology, management and outcomes of VTE using data from a large, observational database. PREFER in VTE was an international, non-interventional disease registry conducted between January 2013 and July 2015 in primary and secondary care across seven European countries. Consecutive patients with acute VTE were documented and followed up over 12 months. PREFER in VTE included 3,455 patients with a mean age of 60.8 ± 17.0 years. Overall, 53.0 % were male. The majority of patients were assessed in the hospital setting as inpatients or outpatients (78.5 %). The diagnosis was deep-vein thrombosis (DVT) in 59.5 % and pulmonary embolism (PE) in 40.5 %. The most common comorbidities were the various types of cardiovascular disease (excluding hypertension; 45.5 %), hypertension (42.3 %) and dyslipidaemia (21.1 %). Following the index VTE, a large proportion of patients received initial therapy with heparin (73.2 %), almost half received a vitamin K antagonist (48.7 %) and nearly a quarter received a DOAC (24.5 %). Almost a quarter of all presentations were for recurrent VTE, with &gt;80 % of previous episodes having occurred more than 12 months prior to baseline. In conclusion, PREFER in VTE has provided contemporary insights into VTE patients and their real-world management, including their baseline characteristics, risk factors, disease history, symptoms and signs, initial therapy and outcomes

Radiative convective equilibrium and organized convection: an observational perspective

Radiative convective equilibrium (RCE) describes a balance between the cooling of the atmosphere by radiation and the heating through latent heat release and surface heat fluxes. While RCE is known to provide an energetic constraint on the atmosphere at the global scale, little is known about the proximity of the atmosphere to RCE at smaller spatial and temporal scales, despite the common use of RCE in idealized modeling studies. Here we provide the first observational evaluation of the scales at which the atmosphere is near RCE. We further use observations of cloud characteristics to investigate the role played by organized convection in the RCE state. While the tropical atmosphere as a whole is near RCE on daily time scales and longer, this is not the case for any given location. Rather, areas in excess of 5,000 × 5,000 km2 must be considered to ensure the atmosphere remains near RCE at least 80% of the time, even for monthly averaged conditions. We confirm that RCE is established through the interplay of regions of active deep convection with high precipitation and weak radiative cooling and regions of subsiding motions leading to shallow cloud states that allow strong radiative cooling with no precipitation. The asymmetry in the maximum amount of radiative cooling and latent heating leads to the well‐known ratio of small areas of precipitation and large regions of subsidence observed in the tropics. Finally, we show that organized deep convection does not occur when regions smaller than 1,000 × 1,000 km2 are near RCE