State-of-the-art regional climate model simulations that are able to resolve key mesoscale circulations are used, for the first time, to understand the interaction between the large-scale convective ...environment of the MJO and processes governing the strong diurnal cycle over the islands of the Maritime Continent (MC). Convection is sustained in the late afternoon just inland of the coasts because of sea breeze convergence. Previous work has shown that the variability in MC rainfall associated with the MJO is manifested in changes to this diurnal cycle; land-based rainfall peaks before the active convective envelope of the MJO reaches the MC, whereas oceanic rainfall rates peak while the active envelope resides over the region. The model simulations show that the main controls on oceanic MC rainfall in the early active MJO phases are the large-scale environment and atmospheric stability, followed by high oceanic latent heat flux forced by high near-surface winds in the later active MJO phases. Over land, rainfall peaks before the main convective envelope arrives (in agreement with observations), even though the large-scale convective environment is only moderately favorable for convection. The causes of this early rainfall peak are strong convective triggers from land–sea breeze circulations that result from high surface insolation and surface heating. During the peak MJO phases cloud cover increases and surface insolation decreases, which weakens the strength of the mesoscale circulations and reduces land-based rainfall, even though the large-scale environment remains favorable for convection at this time. Hence, scale interactions are an essential part of the MJO transition across the MC.
Quantifying flood hazard is an essential component of resilience planning, emergency response, and mitigation, including insurance. Traditionally undertaken at catchment and national scales, ...recently, efforts have intensified to estimate flood risk globally to better allow consistent and equitable decision making. Global flood hazard models are now a practical reality, thanks to improvements in numerical algorithms, global datasets, computing power, and coupled modelling frameworks. Outputs of these models are vital for consistent quantification of global flood risk and in projecting the impacts of climate change. However, the urgency of these tasks means that outputs are being used as soon as they are made available and before such methods have been adequately tested. To address this, we compare multi-probability flood hazard maps for Africa from six global models and show wide variation in their flood hazard, economic loss and exposed population estimates, which has serious implications for model credibility. While there is around 30%-40% agreement in flood extent, our results show that even at continental scales, there are significant differences in hazard magnitude and spatial pattern between models, notably in deltas, arid/semi-arid zones and wetlands. This study is an important step towards a better understanding of modelling global flood hazard, which is urgently required for both current risk and climate change projections.
We present the results of simulations carried out with the Met Office Unified Model at 12, 4 and 1.5 km resolution for a large region centred on West Africa using several different representations of ...the convection processes. These span a range of resolutions from much coarser than the size of the convection processes to cloud‐system‐resolving and thus encompass the intermediate ‘grey zone’. The diurnal cycle in the extent of convective regions in the models is tested against observations from the Geostationary Earth Radiation Budget instrument on Meteosat‐8. By this measure, the two best‐performing simulations are a 12 km model without convective parametrization, using Smagorinsky‐style subgrid‐scale mixing in all three dimensions, and a 1.5 km simulation with two‐dimensional Smagorinsky mixing. Of these, the 12 km model produces a better match to the magnitude of the total cloud fraction but the 1.5 km one results in better timing for its peak value. The results suggest that the previously reported improvement in the representation of the diurnal cycle of convective organization in the 4 km model compared with the standard 12 km configuration is principally a result of the convection scheme employed rather than the improved resolution per se. The details of this result and implications for high‐resolution model simulations are discussed.
A suite of 40 day UK Met Office Unified Model simulations over West Africa during summer 2006 are analyzed to investigate the causes of biases in the position of the rainbelt and to understand the ...role of convection in the regional water budget. The simulations include climate, global operational, and limited area runs (grid spacings from 1.5 to 40 km), including two 12 km runs, one with parameterized and one with explicit convection. The most significant errors in the water cycle terms occur in the simulations with parameterized convection, associated with the diurnal cycle and the location of the convection. Errors in the diurnal cycle increase the northward advection of moisture out of the Sahel toward the Sahara but decrease the advection of moisture into the Sahel from further south, which limits the availability of moisture for Sahelian rainfall. These biases occur within the first 24 h, showing that they originate from the representation of fast physical processes, specifically, the convection scheme. Once these rainfall regimes have been established, the terms of the water budgets act to reinforce the biases, effectively locking the rainbelt's latitude. One of the simulations with parameterized convection does, however, produce a better latitudinal distribution of rainfall because on the first day it is better able to trigger convection in the Sahel. Accurate representation of the diurnal cycle of convection and the ability to trigger convection in a high convective inhibition environment is key to capturing the water cycle of the region and will improve the representation of the West African Monsoon.
Key Points
Simulations are used to understand the West African water cycle
Errors in the convection feedback on the circulation and water cycle
Improving the diurnal cycle of convection will improve the monsoon
Understanding the rapidly changing climate in the Arctic is limited by a lack of understanding of underlying strong feedback mechanisms that are specific to the Arctic. Progress in this field can ...only be obtained by process-level observations; this is the motivation for intensive ice-breaker-based campaigns such as the Arctic Summer Cloud-Ocean Study (ASCOS), described here. However, detailed field observations also have to be put in the context of the larger-scale meteorology, and short field campaigns have to be analysed within the context of the underlying climate state and temporal anomalies from this. To aid in the analysis of other parameters or processes observed during this campaign, this paper provides an overview of the synoptic-scale meteorology and its climatic anomaly during the ASCOS field deployment. It also provides a statistical analysis of key features during the campaign, such as key meteorological variables, the vertical structure of the lower troposphere and clouds, and energy fluxes at the surface. In order to assess the representativity of the ASCOS results, we also compare these features to similar observations obtained during three earlier summer experiments in the Arctic Ocean: the AOE-96, SHEBA and AOE-2001 expeditions. We find that these expeditions share many key features of the summertime lower troposphere. Taking ASCOS and the previous expeditions together, a common picture emerges with a large amount of low-level cloud in a well-mixed shallow boundary layer, capped by a weak to moderately strong inversion where moisture, and sometimes also cloud top, penetrate into the lower parts of the inversion. Much of the boundary-layer mixing is due to cloud-top cooling and subsequent buoyant overturning of the cloud. The cloud layer may, or may not, be connected with surface processes depending on the depths of the cloud and surface-based boundary layers and on the relative strengths of surface-shear and cloud-generated turbulence. The latter also implies a connection between the cloud layer and the free troposphere through entrainment at cloud top.
Abstract
The organization of deep convection and its misrepresentation in many global models is the focus of much current interest. A new method is presented for quantifying convective organization ...based on the identification of convective objects and subsequent derivation of object numbers, areas, and separation distances to describe the degree of convective organization. These parameters are combined into a “convection organization potential” based on the physical principle of an interaction potential between pairs of convective objects. This technique is applied to simulated and observed fields of outgoing longwave radiation (OLR) over the West African monsoon region using data from Met Office Unified Model simulations and satellite observations made by the Geostationary Earth Radiation Budget (GERB) instrument. The method is evaluated by using it to quantify differences between models with different horizontal grid lengths and representations of convection. Distributions of OLR, precipitation and organization parameters, the diurnal cycle of convection, and relationships between the meteorology in different states of organization are compared. Switching from a configuration with parameterized convection to one that allows the model to resolve convective processes at the model grid scale is the leading-order factor improving some aspects of model performance, while increased model resolution is the dominant factor for others. However, no single model configuration performs best compared to observations, indicating underlying deficiencies in both model scaling and process understanding.
In common with many global models, the Met Office Unified Model (MetUM) climate simulations show large errors in Indian summer monsoon rainfall, with a wet bias over the equatorial Indian Ocean, a ...dry bias over India, and with too weak low‐level flow into India. The representation of moist convection is a dominant source of error in global models, where convection must be parametrized, with the errors growing quickly enough to affect both weather and climate simulations. Here we use the first multi‐week continental‐scale MetUM simulations over India, with grid spacings that allow explicit convection, to examine how convective parametrization contributes to model biases in the region.
Some biases are improved in the convection‐permitting simulations with more intense rainfall over India, a later peak in the diurnal cycle of convective rainfall over land, and a reduced positive rainfall bias over the Indian Ocean. The simulations suggest that the reduced rainfall over the Indian Ocean leads to an enhanced monsoon circulation and transport of moisture into India. Increases in latent heating associated with increased convection over land deepen the monsoon trough and enhance water vapour transport into the continent. In addition, delayed continental convection allows greater surface insolation and, along with the same rain falling in more intense bursts, generates a drier land surface. This increases land–sea temperature contrasts, and further enhances onshore flow. Changes in the low‐level water vapour advection into India are dominated by these changes to the flow, rather than to the moisture content in the flow. The results demonstrate the need to improve the representations of convection over both land and oceans to improve simulations of the monsoon.
Loss of summertime Arctic sea ice will lead to a large increase in the emission of aerosols and precursor gases from the ocean surface. It has been suggested that these enhanced emissions will exert ...substantial aerosol radiative forcings, dominated by the indirect effect of aerosol on clouds. Here, we investigate the potential for these indirect forcings using a global aerosol microphysics model evaluated against aerosol observations from the Arctic Summer Cloud Ocean Study (ASCOS) campaign to examine the response of Arctic cloud condensation nuclei (CCN) to sea-ice retreat. In response to a complete loss of summer ice, we find that north of 70° N emission fluxes of sea salt, marine primary organic aerosol (OA) and dimethyl sulfide increase by a factor of ~ 10, ~ 4 and ~ 15 respectively. However, the CCN response is weak, with negative changes over the central Arctic Ocean. The weak response is due to the efficient scavenging of aerosol by extensive drizzling stratocumulus clouds. In the scavenging-dominated Arctic environment, the production of condensable vapour from oxidation of dimethyl sulfide grows particles to sizes where they can be scavenged. This loss is not sufficiently compensated by new particle formation, due to the suppression of nucleation by the large condensation sink resulting from sea-salt and primary OA emissions. Thus, our results suggest that increased aerosol emissions will not cause a climate feedback through changes in cloud microphysical and radiative properties.
STUDY QUESTION
To what extent does oral contraception (OC) impair ovarian reserve parameters in women who seek fertility assessment and counselling to get advice on whether their remaining ...reproductive lifespan is reduced?
SUMMARY ANSWER
Ovarian reserve parameters defined by anti-Müllerian hormone (AMH), antral follicle count (AFC) and ovarian volume were found to be significantly decreased by 19% (95% CI 9.1–29.3%), 18% (95% CI 11.2–24.8%) and 50% (95% CI 45.1–53.7%) among OC users compared with non-users.
WHAT IS KNOWN ALREADY
AMH and AFC have proved to be reliable predictors of ovarian ageing. In women, AMH declines with age and data suggest a relationship with remaining reproductive lifespan and age at menopause. OC may alter parameters related to ovarian reserve assessment but the extent of the reduction is uncertain.
STUDY DESIGN, SIZE, DURATION
A cross-sectional study of 887 women aged 19–46 attending the Fertility Assessment and Counselling Clinic (FACC) from 2011 to 2014 comparing ovarian reserve parameters in OC users with non-OC users.
PARTICIPANTS/MATERIALS, SETTING, METHODS
The FAC Clinic was initiated to provide individual fertility assessment and counselling. All women were examined on a random cycle day by a fertility specialist. Consultation included; transvaginal ultrasound (AFC, ovarian volume, pathology), a full reproductive history and AMH measurement. Women were grouped into non-users and users of OC (all combinations of estrogen-progestin products and the contraceptive vaginal ring). Non-users included women with an intrauterine device (IUD) or no hormonal contraception.
MAIN RESULTS AND THE ROLE OF CHANCE
Of the 887 women, 244 (27.5%) used OC. In a linear regression analyses adjusted for age, ovarian volume was 50% lower (95% CI 45.1–53.7%), AMH was 19% lower (95% CI 9.1–29.3%), and AFC was 18% lower (95% CI 11.2–24.8%) in OC users compared with non-users. Comparison of AMH at values of <10 pmol/l OC was found to have a significant negative influence on AMH (OR 1.6, 95% CI 1.1; 2.4, P = 0.03). Furthermore, we found a significant decrease in antral follicles sized 5–7 mm (P < 0.001) and antral follicles sized 8–10 mm (P < 0.001) but an increase in antral follicles sized 2–4 mm (P = 0.008) among OC users. The two groups (OC users versus non-users) were comparable regarding age, BMI, smoking and maternal age at menopause.
LIMITATIONS, REASON FOR CAUTION
The study population comprised women attending the FAC Clinic. Recruitment was based on self-referral, which could imply a potential selection bias. Ovarian reserve was examined at a random cycle day. However, both AMH and AFC can be assessed independently of the menstrual cycle. The accuracy in predicting residual reproductive lifespan is still needed in both users and non-users of OC.
WIDER IMPLICATIONS OF THE FINDINGS
OC has a major impact on the ovarian volume, and a moderate impact on AFC and AMH with a shift towards the smaller sized antral follicle subclasses. The most evident reduction occurs in the antral follicles of 5–7 and 8–10 mm with the highest number of AMH secreting granulosa cells. It is essential to be aware of the impact of OC use on ovarian reserve parameters when guiding OC users on their fertility status and reproductive lifespan.
STUDY FUNDING/COMPETING INTEREST(S)
The FAC Clinic was established in 2011 as part of the ReproHigh collaboration. This study received funding through the Capital Region Research Fund and by EU-regional funding. There are no competing interests.
TRIAL REGISTRATION NUMBER
The biobank connected to FAC Clinic is approved by the Scientific Ethical Committee (H-1-2011-081).
Background
Photoageing describes complex cutaneous changes which occur following chronic exposure to solar ultraviolet radiation (UVR). Amongst White Northern Europeans, facial photoageing appears as ...distinct clinical phenotypes: ‘hypertrophic’ photoageing (HP) and ‘atrophic’ photoageing (AP). Deep, coarse wrinkles predominate in individuals with HP, whereas those with AP have relatively smooth, unwrinkled skin with pronounced telangiectasia. AP individuals have an increased propensity for developing keratinocyte cancers.
Objectives
To investigate whether histological differences underlie these distinct phenotypes of facial photoageing.
Methods
Facial skin biopsies were obtained from participants with AP (10 M, 10 F; mean age: 78.7 years) or HP (10 M, 10 F; mean age: 74.5 years) and were assessed histologically and by immunohistochemistry.
Results
Demographic characterization revealed 95% of AP subjects, as compared to 35% with HP, were Fitzpatrick skin type I/II; of these, 50% had a history of one or more keratinocyte cancers. There was no history of keratinocyte cancers in the HP cohort. Analysis of UVR‐induced mitochondrial DNA damage confirmed that all volunteers had received similar lifetime cumulative doses of sun exposure. Histologically, male AP had a significantly thicker epidermis than did AP females or those of either sex with HP. HP facial skin exhibited severe solar elastosis, whereas in AP facial skin, solar elastosis was apparent only in females. Loss of papillary dermal fibrillin‐rich microfibrils occurred in all HP and AP female subjects, but not in AP males. Furthermore, male AP had a significant reduction in collagen VII at the dermal–epidermal junction than did AP females or those of either sex with HP.
Conclusions
This study provides further evidence that AP and HP represent distinct clinical and histological entities. Knowledge of these two phenotypes is clinically relevant due to the increased prevalence of keratinocyte cancers in those – particularly males – with the AP phenotype.
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