| 1. |
- Aires, Filipe, et al.
(författare)
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Towards more realistic hypotheses for the information content analysis of cloudy/precipitating situations - Application to a hyperspectral instrument in the microwave
- 2019
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Ingår i: Quarterly Journal of the Royal Meteorological Society. - : Wiley. - 0035-9009 .- 1477-870X. ; 145:718, s. 1-14
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Tidskriftsartikel (refereegranskat)abstract
- Information Content (IC) analysis can be used before an instrument is built to estimate its retrieval uncertainties and analyse their sensitivity to several factors. It is a very useful method to define/optimize satellite instruments. IC has shown its potential to compare instrument concepts in the infrared or the microwave. IC is based on some hypotheses such as the the Gaussian character of the radiative transfer (RT) and instrument errors, the first-guess errors (Gaussian character, std and correlation structure), or the linearization of the RT around a first guess. These hypotheses are easier to define for simple atmospheric situations. However, even in the clear-sky case, their complexity has never ceased to increase towards more realism, to optimize the assimilation of satellite measurements in numerical weather prediction (NWP) systems. In the cloudy/precipitating case, these hypotheses are even more difficult to define in a realistic way as many factors are still very difficult to quantify. In this study, several tools are introduced to specify more realistic IC hypotheses than the current practice. We focus on microwave observations as they are more pertinent for clouds and precipitation. Although not perfect, the proposed solutions are a new step towards more realistic IC assumptions of cloudy/precipitating scenes. A state-dependence of the RT errors is introduced, the first-guess errors have a more complex vertical structure, the IC is performed simultaneously on all the hydrometeors to take into account the contamination effect of the RT input uncertainties, and the IC is performed on a diversified set of cloudy/precipitating scenes with well-defined hydrometeor assumptions. The method presented in this study is illustrated using the HYperspectral Microwave Sensor (HYMS) instrument concept with channels between 6.9 and 874 GHz (millimetre and sub-millimetre regions). HYMS is considered as a potential next generation microwave sounder.
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| 2. |
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| 3. |
- ANDREN, A
(författare)
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THE STRUCTURE OF STABLY STRATIFIED ATMOSPHERIC BOUNDARY-LAYERS - A LARGE-EDDY SIMULATION STUDY
- 1995
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Ingår i: QUARTERLY JOURNAL OF THE ROYAL METEOROLOGICAL SOCIETY. - : ROYAL METEOROLOGICAL SOC. - 0035-9009. ; 121:525, s. 961-985
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Tidskriftsartikel (refereegranskat)abstract
- Dry stably-stratified planetary boundary layers have been studied by large-eddy simulation. Results from simulations using two different subgrid-scale models are compared. A recently suggested improved subgrid-scale model version is shown to give improve
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| 4. |
- Arnqvist, Johan, 1985-, et al.
(författare)
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Flux-profile relation with roughness sublayer correction
- 2015
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Ingår i: Quarterly Journal of the Royal Meteorological Society. - : Wiley. - 0035-9009 .- 1477-870X. ; 141:689, s. 1191-1197
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Tidskriftsartikel (refereegranskat)abstract
- Calculation of momentum flux using Monin–Obukhov similarity theory over forested areas is well known to underestimate the flux. Several suggestions of corrections to the standard flux-profile expression have been proposed in order to increase the magnitude of turbulent flux. The aim of this article is to find a simple, analytical representation for the characteristics of the flow within the canopy layer and the surface layer, including the roughness sublayer. A new form of the roughness sublayer correction is proposed, based on the desire to connect the shape of the roughness sublayer correction to forest characteristics. The new flux-profile relation can be used to find the flux or the wind profile whenever simple and fast estimations are needed, as for mesoscale modelling, scalar transport models, or sound propagation models.
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| 5. |
- Buehler, Stefan, et al.
(författare)
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A concept for a satellite mission to measure cloud ice water path, ice particle size, and cloud altitude
- 2007
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Ingår i: Quarterly Journal of the Royal Meteorological Society. - : Wiley. - 0035-9009 .- 1477-870X. ; 133:S2, s. 109-128
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Tidskriftsartikel (refereegranskat)abstract
- A passive satellite radiometer operating at submillimetre wavelengths can measure cloud ice water path (IWP), ice particle size, and cloud altitude. The paper first discusses the scientific background for such measurements. Formal scientific mission requirements are derived, based on this background and earlier assessments. The paper then presents a comprehensive prototype instrument and mission concept, and demonstrates that it meets the requirements. The instrument is a conically scanning 12-channel radiometer with channels between 183 and 664 GHz, proposed to fly in tandem with one of the Metop satellites. It can measure IWP with a relative accuracy of approximately 20% and a detection threshold of approximately 2 g m−2. The median mass equivalent sphere diameter of the ice particles can be measured with an accuracy of approximately 30 µm, and the median IWP cloud altitude can be measured with an accuracy of approximately 300 m. All the above accuracies are median absolute error values; root mean square error values are approximately twice as high, due to rare outliers.
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| 6. |
- De Luca, Paolo, et al.
(författare)
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Dynamical systems theory sheds new light on compound climate extremes in Europe and Eastern North America
- 2020
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Ingår i: Quarterly Journal of the Royal Meteorological Society. - : Wiley. - 0035-9009 .- 1477-870X. ; 146:729, s. 1636-1650
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Tidskriftsartikel (refereegranskat)abstract
- We propose a novel approach to the study of compound extremes, grounded in dynamical systems theory. Specifically, we present the co‐recurrence ratio (α), which elucidates the dependence structure between variables by quantifying their joint recurrences. This approach is applied to daily climate extremes, derived from the ERA‐Interim reanalysis over the 1979–2018 period. The analysis focuses on concurrent (i.e., same‐day) wet (total precipitation) and windy (10 m wind gusts) extremes in Europe and concurrent cold (2 m temperature) extremes in Eastern North America and wet extremes in Europe. Results for wet and windy extremes in Europe, which we use as a test‐bed for our methodology, show that α peaks during boreal winter. High α values correspond to wet and windy extremes in northwestern Europe, and to large‐scale conditions resembling the positive phase of the North Atlantic Oscillation (NAO). This confirms earlier findings which link the positive NAO to a heightened frequency of extratropical cyclones impacting northwestern Europe. For the Eastern North America–Europe case, α extremes once again reflect concurrent climate extremes – in this case cold extremes over North America and wet extremes over Europe. Our analysis provides detailed spatial information on regional hotspots for these compound extreme occurrences, and encapsulates information on their spatial footprint which is typically not included in a conventional co‐occurrence analysis. We conclude that α successfully characterises compound extremes by reflecting the evolution of the associated meteorological maps. This approach is entirely general, and may be applied to different types of compound extremes and geographical regions.
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| 7. |
- Dey, Dipanjan, et al.
(författare)
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Identification of the atmospheric water sources and pathways responsible for the East Asian summer monsoon rainfall
- 2024
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Ingår i: Quarterly Journal of the Royal Meteorological Society. - 0035-9009 .- 1477-870X. ; 150:759, s. 763-775
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Tidskriftsartikel (refereegranskat)abstract
- The East Asian summer monsoon rainfall provides water security and socio-economic benefit for over 20% of the global population. However, the sources of this rainfall and how it is carried to the East Asian landmass are still uncertain. To address this, atmospheric water sources and pathways associated with the East Asian summer rainfall are identified and quantified in this study using atmospheric water trajectories, calculated with a novel Lagrangian framework. Evaporated water from the East Asian landmass is found to be the major contributor to East Asian rainfall, amounting to local recycling. The results further indicated that the south Indian Ocean is a major non-local source for rainfall over southern East Asia during June to August. The role of the south Indian Ocean as a source of atmospheric water is one of the major findings of the study and would help in better understanding and predicting the East Asian summer rainfall. Evaporated waters from the Pacific Ocean (particularly the far-west Pacific Ocean) dominate the non-local contribution to precipitation over northern East Asia during June to September and over southern East Asian rainfall during September. The spatial structure of the East Asian rainfall is reported to be determined by the atmospheric waters that are evaporated and transported from the non-local sources. The role of the north Indian Ocean and the South Asian landmass as a source of water for East Asian precipitation is minimal and restricted to southern East Asia. The cross-equatorial Somali jet and equatorial trade winds associated with the western North Pacific subtropical high are important pathways for East Asian precipitation sourced over the south Indian Ocean and the Pacific Ocean respectively. In contrast, minor roles are attributed to the Bay of Bengal as a source, and midlatitude westerlies as a transport pathway, for East Asian precipitation. Randomly chosen atmospheric water trajectories were obtained from the backward tracing of the East Asian summer rainfall. These trajectories are a small subset of a total of 5 million trajectories. The green dots are the starting (net precipitation) positions and the blue dots indicate the ending locations (net evaporation) of the trajectories. Basins were defined as the south Indian Ocean (SIO), north Indian Ocean (NIO), South Asia (SA), East Asia (EA), Pacific Ocean (PAC), Atlantic Ocean (ATL). Atmospheric water sources and pathways associated with the East Asian summer rainfall are identified and quantified in this study using a novel Lagrangian framework. The results show the following: (1) Evaporated water from the East Asian landmass is found to be the major contributor to East Asian rainfall, amounting to local recycling. (2) The south Indian Ocean is a major non-local source for rainfall over southern East Asia during June-August. Evaporated waters from the Pacific Ocean dominate the non-local contribution to precipitation over northern East Asia during June-September. (3) The spatial structure of the East Asian rainfall is reported to be determined by the atmospheric waters that are evaporated and transported from the non-local sources. Minor roles are attributed to the Bay of Bengal as a source, and midlatitude westerlies as a transport pathway, for East Asian precipitation.image
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| 8. |
- Ekman, Annica M. L., 1972-, et al.
(författare)
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Influence of horizontal resolution and complexity of aerosol–cloud interactions on marine stratocumulus and stratocumulus-to-cumulus transition in HadGEM3-GC3.1
- 2023
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Ingår i: Quarterly Journal of the Royal Meteorological Society. - 0035-9009 .- 1477-870X. ; 755:149, s. 2049-2066
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Tidskriftsartikel (refereegranskat)abstract
- Stratocumulus (Sc) clouds and stratocumulus-to-cumulus transitions (SCTs) are challenging to represent in global models and they contribute to a large spread in modeled subtropical cloud feedbacks. We evaluate the impact of increasing the horizontal model resolution (∼135, 60 and 25 km, respectively) and increasing the complexity of the aerosol–cloud interaction parameterization (interactive versus non-interactive at medium resolution) on springtime subtropical marine Sc properties and SCTs in the atmosphere-only version of HadGEM3-GC3.1. No significant impact on the spatial location of the SCT could be found between the different model versions. Increasing horizontal resolution led to small but significant increases in liquid water content and a stronger (more negative) shortwave (SW) cloud radiative effect (CRE), in particular over the southern-hemisphere Sc regions. However, for two out of the four studied regions, the stronger SW CRE also brought the model outside the range of satellite-derived values of the SW CRE. Applying non-interactive aerosols instead of interactive aerosols also led to significantly higher liquid water content and a stronger SW CRE over the southern-hemisphere Sc regions, while over the northern-hemisphere Sc regions, a competition between a substantial increase in the cloud droplet number concentration and small changes in the liquid water content resulted in a weaker SW CRE or non-significant changes. In general, using interactive instead of non-interactive aerosol–cloud interactions brought the model closer to satellite-retrieved mean values of the SW CRE. Our results suggest that increasing the horizontal resolution or the complexity of the aerosol–cloud parameterization has a small but statistically significant effect on the SW CRE of marine Sc, in particular over regions with high liquid water content. For these regions, the effect of introducing non-interactive versus interactive aerosol–cloud interactions is about as large as increasing the horizontal resolution from medium to high.
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| 9. |
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| 10. |
- Enger, L, et al.
(författare)
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The response of bora-type flow to sea surface temperature
- 1998
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Ingår i: QUARTERLY JOURNAL OF THE ROYAL METEOROLOGICAL SOCIETY. - : ROYAL METEOROLOGICAL SOC. - 0035-9009. ; 124:548, s. 1227-1244
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Tidskriftsartikel (refereegranskat)abstract
- A non-linear, two-dimensional, hydrostatic, incompressible numerical model with a higher-order turbulence closure scheme is used to study the effect of sea surface temperature on the severe downslope wind called bora at the Adriatic coast. A non-linear la
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