Floods and flash floods are frequent in the south of Europe resulting from heavy rainfall events that often produce more than 200 mm in less than 24 h. Even though the meteorological conditions ...favourable for these situations have been widely studied, there is a lingering question that still arises: what humidity sources could explain so much precipitation? To answer this question, the regional atmospheric Weather Research and Forecasting (WRF) model with a recently implemented moisture tagging capability has been used to analyse the main moisture sources for two catastrophic flood events that occurred during the autumn of 1982 (October and November) in the western Mediterranean area, which is regularly affected by these types of adverse weather episodes. The procedure consists in selecting a priori potential moisture source regions for the extreme event under consideration, and then performing simulations using the tagging technique to quantify the relative contribution of each selected source to total precipitation. For these events we study the influence of four possible potential sources: (1) evaporation in the western Mediterranean; (2) evaporation in the central Mediterranean; (3) evaporation in the North Atlantic; and (4) advection from the tropical and subtropical Atlantic and Africa. Results show that these four moisture sources explain most of the accumulated precipitation, with the tropical and subtropical input being the most relevant in both cases. In the October event, evaporation in the western and central Mediterranean and in the North Atlantic also had an important contribution. However, in the November episode tropical and subtropical moisture accounted for more than half of the total accumulated rainfall, while evaporation in the western Mediterranean and North Atlantic played a secondary role and the contribution of the central Mediterranean was almost negligible. Therefore, remote sources were crucial: in the October event they played a similar role to local sources, whereas in the November case they were clearly dominant. In both episodes, long-distance moisture transport from the tropics and subtropics mostly occurred in mid-tropospheric layers, via well-defined moisture plumes with maximum mixing ratios at medium levels.
We present the main results from the second model intercomparison within the GEWEX (Global Energy and Water cycle EXperiment) Atmospheric Boundary Layer Study (GABLS). The target is to examine the ...diurnal cycle over land in today’s numerical weather prediction and climate models for operational and research purposes. The set-up of the case is based on observations taken during the Cooperative Atmosphere-Surface Exchange Study-1999 (CASES-99), which was held in Kansas, USA in the early autumn with a strong diurnal cycle with no clouds present. The models are forced with a constant geostrophic wind, prescribed surface temperature and large-scale divergence. Results from 30 different model simulations and one large-eddy simulation (LES) are analyzed and compared with observations. Even though the surface temperature is prescribed, the models give variable near-surface air temperatures. This, in turn, gives rise to differences in low-level stability affecting the turbulence and the turbulent heat fluxes. The increase in modelled upward sensible heat flux during the morning transition is typically too weak and the growth of the convective boundary layer before noon is too slow. This is related to weak modelled near-surface winds during the morning hours. The agreement between the models, the LES and observations is the best during the late afternoon. From this intercomparison study, we find that modelling the diurnal cycle is still a big challenge. For the convective part of the diurnal cycle, some of the first-order schemes perform somewhat better while the turbulent kinetic energy (TKE) schemes tend to be slightly better during nighttime conditions. Finer vertical resolution tends to improve results to some extent, but is certainly not the solution to all the deficiencies identified.
The quality control of weather data is a necessity and a responsibility of meteorological services that store, distribute, and use these data. In the present work, a newly designed quality control ...procedure for daily rainfall data is presented after it has been adjusted and tested with more than 10
7
data from 1726 daily rainfall measurement sites in Catalonia. It is applicable to data from different origins (e.g., automatic weather stations or manual historical measurements). The procedure is focused on relative comparison of daily data with reference stations that are automatically selected after an initial estimation of their quality and a proximity study regarding location and correlation. The presented procedure has been verified taking advantage of an available network in the study area that has been routinely quality controlled by technicians of the Meteorological Service of Catalonia. The newly designed quality control procedure for daily precipitation yields good results, especially for extreme values: type I error under 10% is found for values up to 150 mm (error decreasing for lower values) and type II error is under 16% when reported values are twice a measure of 50 mm or more (error decreasing for more extreme values). After the application of the quality control procedure, a selection of series with the minimum desired quality is achieved.
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Abstract
On 28 November 2012, a multivortex EF3 tornado occurred in southeastern Italy causing one fatality and estimated damage of 60 million euros. At approximately 1050 LT (0950 UTC), this ...tornado, which initially formed in association with a supercell thunderstorm over the Ionian Sea, moved inland. The environment where the tornadic supercell developed was characterized by large vertical wind shear in the lowest 1 km of the atmosphere and moderate conditional instability. Mesoscale-model numerical simulations show that it is possible to produce a simulated supercell thunderstorm with a track, change in intensity, and evolution similar to the actual one that spawned the tornado in Taranto, southern Italy. The genesis of the simulated supercell is due to a combination of mesoscale meteorological features: warm low-level air advected toward the Ionian Sea, combined with midlevel cooling due to an approaching trough, increased the potential instability; the intense vertical shear favored the possibility of supercell development; and boundary layer rolls over the Ionian Sea moved in phase with the cells produced by the orography of Calabria to supply ascent, moisture, and heat to the convection. An unusual feature of the present case is the central role of the orography, which was verified in a sensitivity experiment where it was reduced by 80%.
We evaluate planetary boundary-layer (PBL) parametrizations in the Weather Research and Forecasting (WRF) numerical model, with three connected objectives: first, for a 16-year period, we use a ...cluster analysis algorithm of three-day back-trajectories to determine general synoptic flow patterns over Barcelona, Spain arriving at heights of 0.5, 1.5, and 3 km; to represent the lower PBL, upper PBL, and lower free troposphere, respectively. Seven clusters are determined at each arriving altitude. Regional recirculations account for 54 % of the annual total at 0.5 km, especially in summertime. In the second objective, we assess a time-adaptive approach using an extended Kalman filter to estimate PBL height from backscatter lidar returns at 1200 UTC
±
30 min for 45 individual days during a seven-year period. PBL heights retrieved with this technique are compared with three classic methods used in the literature to estimate PBL height from lidar. The methods are validated against PBL heights calculated from daytime radiosoundings. Lidar and radiosonde estimated PBL heights are classified under objectively-determined synoptic clusters. With the final objective, WRF model-simulated PBL heights are validated against lidar estimates using eight unique PBL schemes as inputs. Evaluation of WRF model-simulated PBL heights are performed under different synoptic situations. Determination coefficients with lidar estimates indicate the non-local assymetric convective model scheme is the most reliable, with the widely-tested local Mellor–Yamada–Janjic scheme showing the weakest correlations with lidar retrievals. Overall, there is a systematic underestimation of PBL height simulated in the WRF model.
•Urban morphology has the highest impact on UHI intensity in Mediterranean climate.•UHI intensity can be estimated based on three descriptors of urban morphology.•Climate performance of urban ...textures varies in summer time and winter time.•Compactness and vertical density are key morphological features for UHI assessment.
Urban heat island effect is almost always neglected in building energy simulations, due to difficulties in obtaining site-specific climate data with a district-scale resolution. This study aims at filling this gap for the Mediterranean urban context, presenting a set of tools to estimate the climatic performance of urban fabric at the local scale.
The results are based on climatic analysis conducted in Rome (Italy) and Barcelona (Spain) with the Urban Weather Generator (UWG) model, validated using temperature measurements taken in urban meteorological stations. Parametric analysis of the UHI intensity was performed considering five key variables: urban morphology, vegetation cover, anthropogenic heat from buildings, anthropogenic heat from traffic and albedo. The results show that the variability of urban morphology has the major impact on urban temperature. Two robust relationships between three morphology descriptors of urban fabric and UHI intensity were established applying multiple regression analysis. Such relationships indicate that both the horizontal and the vertical density of buildings play a major role on the temperature increase in urban areas.
Easy-to-use graphical tools have been provided to compare the climate performance of different urban textures and to estimate the average UHI intensity variability in Mediterranean cities.
The second edition of Mesoscale Meteorological Modeling is a fully revised resource for researchers and practitioners in the growing field of meteorological modeling at the mesoscale. Pielke has ...enhanced the new edition by quantifying model capability (uncertainty) by a detailed evaluation of the assumptions of parameterization and error propagation. Mesoscale models are applied in a wide variety of studies, including weather prediction, regional and local climate assessments, and air pollution investigations.
Volatile organic compounds (VOCs) are reactive trace gases abundant in the atmosphere. As strongly reactive constituents they have many impacts on the atmospheric chemistry. To properly understand ...the processes involved in VOC cycles within the biosphere and atmosphere, we must have comprehensive knowledge on the biogenic and anthropogenic emissions and atmospheric concentrations. In this thesis, the emissions of VOCs were measured in many scales from various Fennoscandian ecosystems, utilizing several methods. First, enclosure method was applied to study the branch scale VOC emission from mountain birch. The measurements were conducted during two successive growing seasons. Significant emissions of sesquiterpenes were observed in the first year but not in the second one. Second, relaxed eddy accumulation (REA) method was used to study the ecosystem scale emissions of light hydrocarbons from a wetland. In addition to methane, the only significant emission was that of isoprene. Isoprene emission potential was found to be about 680 μg m-2 h-1. The REA method was further developed by studying the possible stability dependency of the method. Another ecosystem scale flux measurement method, disjunct eddy accumulation (DEA), was applied to study monoterpene emissions from a timber felling area. The emissions of monoterpenes were very high for a few months after felling, peaking at 5200 μg m−2 h−1. Despite of the short period those emissions seem to be of great importance for the atmospheric VOC burden. Third, profiles of boundary layer concentrations of some biogenic and anthropogenic VOCs were measured using a hot air balloon as a platform. Landscape scale emissions were inferred using the concentration data. Overall, our understanding of the previously poorly known VOC emissions from some Fennoscandian ecosystems was increased. This study highlights the importance to quantify emission hotspots of even marginal ecosystems to get comprehensive understanding for emission inventories and future redictions. The correct choice of measuring methods and experiment setup is essential for reliable field data.
Haihtuvat orgaaniset yhdisteet (Volatile Organic Compound, VOC) ovat ilmakehässä esiintyviä reaktiivisia hivenkaasuja. Voimakkaasti reaktiivisina aineina niillä on monia vaikutuksia ilmakehän kemiaan. Ymmärtääksemme kunnolla niiden reaktioita biosfäärissä ja ilmakehässä, meillä on oltava hyvä käsitys niiden lähteistä ja ilmapitoisuuksista. Tässä työssä mitattiin VOC päästöjä erilaisista ekosysteemeistä Fennoskandian alueella käyttäen lukuisia eri menetelmiä. Kammiomenetelmää käytettiin tutkittaessa yksittäisten oksien VOC päästöjä tunturikoivusta. Mittauksia tehtiin kahtena peräkkäisen kasvukautena. Ensimmäisenä tutkimusvuonna havaittiin merkittäviä seskviterpeenipäästöjä, mutta toisena tutkimusvuonna niitä ei enää havaittu. Relaxed Eddy Accumulation (REA) menetelmää käytettiin tutkittaessa kevyiden hiilivetyjen ekosysteemiskaalan päästöjä suolta. Metaanin lisäksi vain isopreenin päästö oli merkittävä. Isopreenin emissiopotentiaali oli noin 680 μg m-2 h-1. REA-menetelmää kehitettiin edelleen tutkimalla sen herkkyyttä ilmakehän stabiiliuteen. Toista ekosysteemiskaalan mittausmenetelmää, Disjunct Eddy Accumulation (DEA), käytettiin tutkittaessa monoterpeenipäästöjä hakatusta metsästä. Monoterpeenien päästö oli huomattavan suuri, jopa 5200 μg m-2 h-1, muutaman kuukauden ajan hakkuun jälkeen. Lyhyestä ajanjaksosta huolimatta hakkuualueiden päästöt näyttäisivät olevan merkittäviä ilmakehän monoterpeenikuormitukselle. Useiden biogeenisten ja antropogeenisten VOC-yhdisteiden pitoisuuksien pystygradientteja mitattiin ilmakehän rajakerroksessa käyttäen kuumailmapalloa mittausalustana. Laajan skaalan päästöjä arvioitiin käyttämällä näitä pitoisuustietoja. Tämän työn myötä tietämyksemme eräiden ennestään heikosti tunnettujen Fennoskandian ekosysteemien VOC-päästöistä parani. Tämä tutkimus korostaa myös voimakkaiden, mutta pienialaisten päästölähteiden tuntemisen tärkeyttä. Luotettavan kenttämittaustiedon saamiseksi oikeiden mittausmenetelmien valinta ja tutkimuksen huolellinen suunnittelu on avainasemassa.
The most widely used technique for nowcasting of quantitative precipitation in operational and research centers is the Lagrangian extrapolation of the latest radar observations. However, this ...technique has a limited forecast skill because of the assumption made on its formulation, such as the fact that the motion vectors do not change and, even more important for convective events, neglect any growth or decay in the precipitation field. In this work, the McGill Algorithm for Precipitation Nowcasting by Lagrangian Extrapolation (MAPLE) errors have been computed for 10 yr of radar composite data over the continental United States. The study of these errors shows systematic bias depending on the time of day. This effect is related to the solar cycle, whose heating energy results in an increase in the average rainfall in the afternoon. This external forcing interacts with the atmospheric system, creating local initiation and dissipation of convection depending on orography, land use, cloud coverage, etc. The signal of the diurnal cycle in MAPLE precipitation forecast has been studied in different locations and spatial scales as a function of lead time in order to recognize where, when, and for which spatial scales the signal is significant. This information has been used in the development of a scaling correction scheme where the mean errors due to the diurnal cycle are adjusted. The results show that the developed methodology improves the forecast for the spatial scales and locations where the diurnal cycle signal is significant.
In response to Caesar, who intends to reach Antonius in Italy, the boatman Amyclas sets out the celestial and terrestrial signs that foretell a storm and advises against putting out to sea (Luc. ...5.539‒560). In this speech Lucan draws on the treatment of such phenomena in the didactic poems of Aratus and Vergil, but the allusions are remodelled in epic language and adapted to the narrative context of the episode. Further, in the story of Amyclas Lucan develops dramatic ideas mentioned in the specific passages in which Aratus and Vergil reflect on the utility of their teachings. Thus the boatman’s meteorological
is highlighted, though he is unable to gain any advantage from it. In fact, in contrast to Palinurus with Aeneas in
5 and to the
with Pompey in Luc. 8, Amyclas does not try to dissuade Caesar from the voyage and agrees to accompany him. His speech shows affinities with declamations on the theme of sailing and the presence of adverse omens; however, the speech of Amyclas sounds like a
that has been interrupted. This aspect focuses the impossibility of communication between the two characters: Amyclas, powerlessly external to the civil wars, can only appeal to the force of nature, which Caesar impiously defies.
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