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  • 1
    Online Resource
    Online Resource
    Sub‐km scale numerical weather prediction model simulations of radiation fog
    Wiley ; 2021
    In:  Quarterly Journal of the Royal Meteorological Society Vol. 147, No. 735 ( 2021-01), p. 746-763
    Details
    In: Quarterly Journal of the Royal Meteorological Society, Wiley, Vol. 147, No. 735 ( 2021-01), p. 746-763
    Abstract: The numerical weather prediction (NWP) of fog remains a challenge, with accurate forecasts relying on the representation of many interacting physical processes. The recent Local And Non‐local Fog EXperiment (LANFEX) has generated a detailed observational dataset, creating a unique opportunity to assess the NWP of fog events. We evaluate the performance of operational and research configurations of the Met Office Unified Model (MetUM) with three horizontal grid lengths, 1.5 km and 333 and 100 m, in simulating four LANFEX case studies. In general, the subkilometre (sub‐km) scale versions of MetUM are in better agreement with the observations; however, there are a number of systematic model deficiencies. MetUM produces valleys that are too warm and hills that are too cold, leading to valleys that do not have enough fog and hills that have too much. A large sensitivity to soil temperature was identified from a set of parametrisation sensitivity experiments. In all the case studies, the model erroneously transfers heat too readily through the soil to the surface, preventing fog formation. Sensitivity tests show that the specification of the soil thermal conductivity parametrisation can lead to up to a 5‐hr change in fog onset time. Overall, the sub‐km models demonstrate promise, but they have a high sensitivity to surface properties.
    Type of Medium: Online Resource
    ISSN: 0035-9009 , 1477-870X
    URL: Issue
    URL: Article
    DOI: 10.1002/qj.v147.735
    DOI: 10.1002/qj.3943
    RVK:
    UA 1000
    RVK:
    UA 7650
    Language: English
    Publisher: Wiley
    Publication Date: 2021
    detail.hit.zdb_id: 3142-2
    detail.hit.zdb_id: 2089168-4
    SSG: 14
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  • 2
    Online Resource
    Online Resource
    A Pan-African Convection-Permitting Regional Climate Simulation with the Met Office Unified Model: CP4-Africa
    American Meteorological Society ; 2018
    In:  Journal of Climate Vol. 31, No. 9 ( 2018-05-01), p. 3485-3508
    Details
    In: Journal of Climate, American Meteorological Society, Vol. 31, No. 9 ( 2018-05-01), p. 3485-3508
    Abstract: A convection-permitting multiyear regional climate simulation using the Met Office Unified Model has been run for the first time on an Africa-wide domain. The model has been run as part of the Future Climate for Africa (FCFA) Improving Model Processes for African Climate (IMPALA) project, and its configuration, domain, and forcing data are described here in detail. The model [Pan-African Convection-Permitting Regional Climate Simulation with the Met Office UM (CP4-Africa)] uses a 4.5-km horizontal grid spacing at the equator and is run without a convection parameterization, nested within a global atmospheric model driven by observations at the sea surface, which does include a convection scheme. An additional regional simulation, with identical resolution and physical parameteriza tions to the global model, but with the domain, land surface, and aerosol climatologies of CP4-Africa, has been run to aid in the understanding of the differences between the CP4-Africa and global model, in particular to isolate the impact of the convection parameterization and resolution. The effect of enforcing moisture conservation in CP4-Africa is described and its impact on reducing extreme precipitation values is assessed. Preliminary results from the first five years of the CP4-Africa simulation show substantial improvements in JJA average rainfall compared to the parameterized convection models, with most notably a reduction in the persistent dry bias in West Africa, giving an indication of the benefits to be gained from running a convection-permitting simulation over the whole African continent.
    Type of Medium: Online Resource
    ISSN: 0894-8755 , 1520-0442
    URL: Article
    DOI: 10.1175/JCLI-D-17-0503.1
    RVK:
    UA 4548
    Language: English
    Publisher: American Meteorological Society
    Publication Date: 2018
    detail.hit.zdb_id: 246750-1
    detail.hit.zdb_id: 2021723-7
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  • 3
    Online Resource
    Online Resource
    The Role of Precipitation in Controlling the Transition from Stratocumulus to Cumulus Clouds in a Northern Hemisphere Cold-Air Outbreak
    American Meteorological Society ; 2017
    In:  Journal of the Atmospheric Sciences Vol. 74, No. 7 ( 2017-07-01), p. 2293-2314
    Details
    In: Journal of the Atmospheric Sciences, American Meteorological Society, Vol. 74, No. 7 ( 2017-07-01), p. 2293-2314
    Abstract: Aircraft observations in a cold-air outbreak to the north of the United Kingdom are used to examine the boundary layer and cloud properties in an overcast mixed-phase stratocumulus cloud layer and across the transition to more broken open-cellular convection. The stratocumulus cloud is primarily composed of liquid drops with small concentrations of ice particles and there is a switch to more glaciated conditions in the shallow cumulus clouds downwind. The rapid change in cloud morphology is accompanied by enhanced precipitation with secondary ice processes becoming active and greater thermodynamic gradients in the subcloud layer. The measurements also show a removal of boundary layer accumulation mode aerosols via precipitation processes across the transition that are similar to those observed in the subtropics in pockets of open cells. Simulations using a convection-permitting (1.5-km grid spacing) regional version of the Met Office Unified Model were able to reproduce many of the salient features of the cloud field although the liquid water path in the stratiform region was too low. Sensitivity studies showed that ice was too active at removing supercooled liquid water from the cloud layer and that improvements could be made by limiting the overlap between the liquid water and ice phases. Precipitation appears to be the key mechanism responsible for initiating the transition from closed- to open-cellular convection by decoupling the boundary layer and depleting liquid water from the stratiform cloud.
    Type of Medium: Online Resource
    ISSN: 0022-4928 , 1520-0469
    URL: Article
    URL: Article
    DOI: 10.1175/JAS-D-16-0362.1
    DOI: 10.1175/JAS-D-16-0362.s1
    RVK:
    UA 4800
    Language: English
    Publisher: American Meteorological Society
    Publication Date: 2017
    detail.hit.zdb_id: 218351-1
    detail.hit.zdb_id: 2025890-2
    SSG: 16,13
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  • 4
    Online Resource
    Online Resource
    An operational fog prediction system for Delhi using the 330 m Unified Model
    Wiley ; 2018
    In:  Atmospheric Science Letters Vol. 19, No. 1 ( 2018-01)
    Details
    In: Atmospheric Science Letters, Wiley, Vol. 19, No. 1 ( 2018-01)
    Abstract: We introduce the National Centre for Medium Range Weather Forecasting's (NCMRWF) high‐resolution (330 m) Unified Model implementation targeted at fog and visibility prediction over Delhi, the “Delhi Model” (DM). The requirement for running the DM in real time is that Delhi is highly vulnerable to fog‐related issues and that low visibility conditions affect both airborne and ground transport during winter months. Enhanced orographic features at 330 m resolution, in conjunction with other surface boundary conditions used by the DM, have led to improvements in the simulation of spatio‐temporal variability of visibility. During the winter season, the increased levels of pollution can have a significant impact on fog, or smog formation. Sensitivity experiments carried out using specified aerosol mass concentrations show that the visibility predicted by the DM is highly sensitive to the presence of aerosol. The impact of the urban heat island on visibility prediction is also investigated using recent high‐resolution land use data from the Indian Space Research Organisation (ISRO) in the model.
    Type of Medium: Online Resource
    ISSN: 1530-261X , 1530-261X
    URL: Issue
    URL: Article
    DOI: 10.1002/asl.2018.19.issue-1
    DOI: 10.1002/asl.796
    Language: English
    Publisher: Wiley
    Publication Date: 2018
    detail.hit.zdb_id: 2025884-7
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  • 5
    Online Resource
    Online Resource
    Understanding London's summertime cloud cover
    Wiley ; 2022
    In:  Quarterly Journal of the Royal Meteorological Society Vol. 148, No. 742 ( 2022-01), p. 454-465
    Details
    In: Quarterly Journal of the Royal Meteorological Society, Wiley, Vol. 148, No. 742 ( 2022-01), p. 454-465
    Abstract: Cities are a source of complex land–atmosphere interactions. Spatial differences in the energy balance and enhanced surface roughness interact with the atmosphere to alter clouds and precipitation. Here, we explore how London (UK) alters cloud formation during the spring and summer. The Met Office's high‐resolution operational forecasts predict enhanced cloud cover over the city, as found in observations, but underpredicts the intensity. During low wind speeds, cloud enhancement over the city is strongest and linked to an urban‐induced thermal circulation. These circulations advect moist air from the city edge inwards, transporting it upwards with a large moisture convergence over the urban area. At around 1,000 m above the surface, the turbulent moisture flux takes over the moisture transport to the cloud layer. A relative humidity budget shows the moisture flux in the upper boundary layer to be the largest contribution to the urban–rural differences in relative humidity.
    Type of Medium: Online Resource
    ISSN: 0035-9009 , 1477-870X
    URL: Issue
    URL: Article
    DOI: 10.1002/qj.v148.742
    DOI: 10.1002/qj.4214
    RVK:
    UA 1000
    RVK:
    UA 7650
    Language: English
    Publisher: Wiley
    Publication Date: 2022
    detail.hit.zdb_id: 3142-2
    detail.hit.zdb_id: 2089168-4
    SSG: 14
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  • 6
    Online Resource
    Online Resource
    Longitudinally Asymmetric Stratospheric Oscillation on a Tidally Locked Exoplanet
    American Astronomical Society ; 2022
    In:  The Astrophysical Journal Vol. 930, No. 2 ( 2022-05-01), p. 152-
    Details
    In: The Astrophysical Journal, American Astronomical Society, Vol. 930, No. 2 ( 2022-05-01), p. 152-
    Abstract: Using a three-dimensional general circulation model, we show that the atmospheric dynamics on a tidally locked Earth-like exoplanet, simulated with the planetary and orbital parameters of Proxima Centauri b, support a longitudinally asymmetric stratospheric wind oscillation (LASO), analogous to Earth’s quasi-biennial oscillation (QBO). In our simulations, the LASO has a vertical extent of 35–55 km, a period of 5–6.5 months, and a peak-to-peak wind speed amplitude of −70 to +130 m s −1 with a maximum at an altitude of 41 km. Unlike the QBO, the LASO displays longitudinal asymmetries related to the asymmetric thermal forcing of the planet and to interactions with the resulting stationary Rossby waves. The equatorial gravity wave sources driving the LASO are localized in the deep convection region at the substellar point and in a jet exit region near the western terminator, unlike the QBO, for which these sources are distributed uniformly around the planet. Longitudinally, the western terminator experiences the highest wind speeds and undergoes reversals earlier than other longitudes. The antistellar point only experiences a weak oscillation with a very brief, low-speed westward phase. The QBO on Earth is associated with fluctuations in the abundances of water vapor and trace gases such as ozone, which are also likely to occur on exoplanets if these gases are present. Strong fluctuations in temperature and the abundances of atmospheric species at the terminators will need to be considered when interpreting atmospheric observations of tidally locked exoplanets.
    Type of Medium: Online Resource
    ISSN: 0004-637X , 1538-4357
    URL: Article
    DOI: 10.3847/1538-4357/ac625d
    RVK:
    UA 1000
    Language: Unknown
    Publisher: American Astronomical Society
    Publication Date: 2022
    detail.hit.zdb_id: 2207648-7
    detail.hit.zdb_id: 1473835-1
    SSG: 16,12
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  • 7
    Online Resource
    Online Resource
    Towards retrieving critical relative humidity from ground‐based remote‐sensing observations
    Wiley ; 2016
    In:  Quarterly Journal of the Royal Meteorological Society Vol. 142, No. 700 ( 2016-10), p. 2867-2881
    Details
    In: Quarterly Journal of the Royal Meteorological Society, Wiley, Vol. 142, No. 700 ( 2016-10), p. 2867-2881
    Abstract: Nearly all large‐scale cloud parametrizations require the specification of the critical relative humidity (RHcrit). This is the grid‐box mean relative humidity at which the subgrid fluctuations in temperature and water vapour are assumed to become so large that part of a subsaturated grid box becomes saturated and cloud starts to form. Until recently, the lack of high‐resolution observations of temperature and moisture variability has hindered achievement of a reasonable estimate of RHcrit. However, the advent of ground‐based Raman lidar now allows the acquisition of long records of temperature and moisture with subminute sample rates. Lidar observations are inherently noisy and any analysis of higher‐order moments will be dependent on the ability to quantify and remove this noise. We present an exploratory study aimed at understanding whether current noise levels of lidar‐retrieved temperature and water vapour are sufficiently low to obtain a reasonable estimate of RHcrit. We show that vertical profiles of RHcrit can be derived with an uncertainty of a few per cent. RHcrit tends to be smallest near the boundary‐layer top and seems to be insensitive to the horizontal grid spacing at the scales investigated here (30–120 km). However, larger sensitivity was found to the vertical grid spacing. RHcrit is observed to decrease by 10% as the vertical grid spacing quadruples. By way of example, the lidar‐retrieved RHcrit profiles were used to evaluate a parametrization that estimates RHcrit from variances diagnosed from the boundary‐layer parametrization. It is shown that this parametrization overestimates RHcrit by up to 10%, but captures the diurnal variability of RHcrit well, with lower values of RHcrit near the boundary‐layer top. While we show that the uncertainties associated with the retrievals are large, lidar observations seem promising to diagnose and evaluate a very important parameter to predict cloud fraction in climate and numerical weather prediction models.
    Type of Medium: Online Resource
    ISSN: 0035-9009 , 1477-870X
    URL: Issue
    URL: Article
    DOI: 10.1002/qj.2016.142.issue-700
    DOI: 10.1002/qj.2874
    RVK:
    UA 1000
    RVK:
    UA 7650
    Language: English
    Publisher: Wiley
    Publication Date: 2016
    detail.hit.zdb_id: 3142-2
    detail.hit.zdb_id: 2089168-4
    SSG: 14
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  • 8
    Online Resource
    Online Resource
    Exploring the climate of Proxima B with the Met Office Unified Model
    EDP Sciences ; 2017
    In:  Astronomy & Astrophysics Vol. 601 ( 2017-5), p. A120-
    Details
    In: Astronomy & Astrophysics, EDP Sciences, Vol. 601 ( 2017-5), p. A120-
    Type of Medium: Online Resource
    ISSN: 0004-6361 , 1432-0746
    URL: Article
    DOI: 10.1051/0004-6361/201630020
    RVK:
    UA 1000
    RVK:
    US 1090
    Language: English
    Publisher: EDP Sciences
    Publication Date: 2017
    detail.hit.zdb_id: 1458466-9
    SSG: 16,12
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  • 9
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    Online Resource
    The TRAPPIST-1 Habitable Atmosphere Intercomparison (THAI). II. Moist Cases—The Two Waterworlds
    American Astronomical Society ; 2022
    In:  The Planetary Science Journal Vol. 3, No. 9 ( 2022-09-01), p. 212-
    Details
    In: The Planetary Science Journal, American Astronomical Society, Vol. 3, No. 9 ( 2022-09-01), p. 212-
    Abstract: To identify promising exoplanets for atmospheric characterization and to make the best use of observational data, a thorough understanding of their atmospheres is needed. Three-dimensional general circulation models (GCMs) are one of the most comprehensive tools available for this task and will be used to interpret observations of temperate rocky exoplanets. Due to parameterization choices made in GCMs, they can produce different results, even for the same planet. Employing four widely used exoplanetary GCMs—ExoCAM, LMD-G, ROCKE-3D, and the UM—we continue the TRAPPIST-1 Habitable Atmosphere Intercomparison by modeling aquaplanet climates of TRAPPIST-1e with a moist atmosphere dominated by either nitrogen or carbon dioxide. Although the GCMs disagree on the details of the simulated regimes, they all predict a temperate climate with neither of the two cases pushed out of the habitable state. Nevertheless, the intermodel spread in the global mean surface temperature is nonnegligible: 14 K and 24 K in the nitrogen- and carbon dioxide-dominated case, respectively. We find substantial intermodel differences in moist variables, with the smallest amount of clouds in LMD-Generic and the largest in ROCKE-3D. ExoCAM predicts the warmest climate for both cases and thus has the highest water vapor content and the largest amount and variability of cloud condensate. The UM tends to produce colder conditions, especially in the nitrogen-dominated case due to a strong negative cloud radiative effect on the day side of TRAPPIST-1e. Our study highlights various biases of GCMs and emphasizes the importance of not relying solely on one model to understand exoplanet climates.
    Type of Medium: Online Resource
    ISSN: 2632-3338
    URL: Article
    DOI: 10.3847/PSJ/ac6cf2
    Language: Unknown
    Publisher: American Astronomical Society
    Publication Date: 2022
    detail.hit.zdb_id: 3021068-9
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  • 10
    Online Resource
    Online Resource
    Processes Controlling Tropical Tropopause Temperature and Stratospheric Water Vapor in Climate Models
    American Meteorological Society ; 2015
    In:  Journal of Climate Vol. 28, No. 16 ( 2015-08-15), p. 6516-6535
    Details
    In: Journal of Climate, American Meteorological Society, Vol. 28, No. 16 ( 2015-08-15), p. 6516-6535
    Abstract: A warm bias in tropical tropopause temperature is found in the Met Office Unified Model (MetUM), in common with most models from phase 5 of CMIP (CMIP5). Key dynamical, microphysical, and radiative processes influencing the tropical tropopause temperature and lower-stratospheric water vapor concentrations in climate models are investigated using the MetUM. A series of sensitivity experiments are run to separate the effects of vertical advection, ice optical and microphysical properties, convection, cirrus clouds, and atmospheric composition on simulated tropopause temperature and lower-stratospheric water vapor concentrations in the tropics. The numerical accuracy of the vertical advection, determined in the MetUM by the choice of interpolation and conservation schemes used, is found to be particularly important. Microphysical and radiative processes are found to influence stratospheric water vapor both through modifying the tropical tropopause temperature and through modifying upper-tropospheric water vapor concentrations, allowing more water vapor to be advected into the stratosphere. The representation of any of the processes discussed can act to significantly reduce biases in tropical tropopause temperature and stratospheric water vapor in a physical way, thereby improving climate simulations.
    Type of Medium: Online Resource
    ISSN: 0894-8755 , 1520-0442
    URL: Article
    DOI: 10.1175/JCLI-D-15-0075.1
    RVK:
    UA 4548
    Language: English
    Publisher: American Meteorological Society
    Publication Date: 2015
    detail.hit.zdb_id: 246750-1
    detail.hit.zdb_id: 2021723-7
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