•Rainfall partitioning is the most influenced by amount of rainfall and its intensity.•Drop diameter and velocity significantly influenced rainfall partitioning.•Affecting variables differ among ...vegetation periods and tree species.
Rainfall partitioning is an important part of the ecohydrological cycle, influenced by numerous variables. Rainfall partitioning for pine (Pinus nigra Arnold) and birch (Betula pendula Roth.) trees was measured from January 2014 to June 2017 in an urban area of Ljubljana, Slovenia. 180 events from more than three years of observations were analyzed, focusing on 13 meteorological variables, including the number of raindrops, their diameter, and velocity. Regression tree and boosted regression tree analyses were performed to evaluate the influence of the variables on rainfall interception loss, throughfall, and stemflow in different phenoseasons. The amount of rainfall was recognized as the most influential variable, followed by rainfall intensity and the number of raindrops. Higher rainfall amount, intensity, and the number of drops decreased percentage of rainfall interception loss. Rainfall amount and intensity were the most influential on interception loss by birch and pine trees during the leafed and leafless periods, respectively. Lower wind speed was found to increase throughfall, whereas wind direction had no significant influence. Consideration of drop size spectrum properties proved to be important, since the number of drops, drop diameter, and median volume diameter were often recognized as important influential variables.
The theoretical basis for describing natural steady-state conditions in caves as well as for their changes in time that follow from the simple advection-diffusion equation, is given. The impacts of ...visits to caves – direct impacts due to anthropogenic emissions of heat and CO2, as well as indirect ones, such as illumination and possible drafts when opening the door to the cave – are estimated in dependence to the number of visitors and the size of the cave: the size with which the effects of the visits are below the detection threshold is estimated. It is shown that the sources cause linear responses, while the consequences of the exchange with the walls of the cave or with the exterior depend on time exponentially. Characteristic times for linear as well as for exponential responses are roughly estimated.
Tourism activities in caves can result in changes in the microclimates of caves. The natural microclimate in closed caves is constant due to the balance between cave air and cave walls, while in open ...caves exchanges with outside air influence the microclimate. Visits to caves, especially in closed smaller caves, can thus endanger the natural balance if the microclimate does not return to natural conditions quickly enough.Continuous monitoring of the temperature and concentration of carbon dioxide in Škocjan Caves enables the assessment of the impact of visits. For this purpose, we used data measured in the relatively closed Silent Cave, at the locations named Calvary (Kalvarija), Tent (Šotor), and Passage (Prehod) in 2016, and in the wide open Murmuring Cave, at the locations named Bridge (Most) and Rimstone Pools (Ponvice), in 2013. The outdoor air temperature, as measured at the Škocjan meteorological station on the surface plateau, was considered in both cases. Along the tourist part of Škocjan Caves, the most closed part of the cave in Silent Cave is the location at Calvary, when the entrance doors through an artificially dug tunnel are closed. During the visits, the microclimate is subjected to draughts through open doors and to anthropogenic emissions. The data suggest that the influence of draughts predominates over direct anthropogenic emissions. In winter or on cold days air flows upwards and through the tunnel out of the cave, whereas in summer or on warm days it flows downwards. In such cases, the CO2 concentration decreases markedly due to the downwards chimney effect as the concentration in the outside air is much lower than in the cave. The data show that the temperature overnight and towards morning always returns to its natural value even in this
rather small location in the cave. The changes in CO2 concentration persist for a longer period, until the time of the first visit the next morning, when it is again perturbed by a new visit. The data on time courses support the theoretically estimated characteristic of the exponential decline of disturbances backward towards natural conditions, depending on the size of a cave and on the efficiency of exchanges with its walls. For temperature, this characteristic time tT is about three to six hours at the Calvary site. The return of CO2 to natural conditions tCO2 is longer and its estimate less reliable than the one for temperature. In the wide-open and large Murmuring Cave, the impact of visits is negligible throughout the year. In this part of the cave we can observe the influence of external daily and annual changes, the amplitudes of which get smaller, and their phase lags bigger, deeper in the cave.
The study presents a precipitation intercomparison based on two satellite-derived datasets (TRMM 3B42, CMORPH), four raingauge-based datasets (GPCC, E-OBS, Willmott & Matsuura, CRU), ERA Interim ...reanalysis (ERAInt), and a single climate simulation using the WRF model. The comparison was performed for a domain encompassing parts of Europe and the North Atlantic over the 11-year period of 2000–2010. The four raingauge-based datasets are similar to the TRMM dataset with biases over Europe ranging from –7 % to +4 %. The spread among the raingauge-based datasets is relatively small over most of Europe, although areas with greater uncertainty (more than 30 %) exist, especially near the Alps and other mountainous regions. There are distinct differences between the datasets over the European land area and the Atlantic Ocean in comparison to the TRMM dataset. ERAInt has a small dry bias over the land; the WRF simulation has a large wet bias (+30 %), whereas CMORPH is characterized by a large and spatially consistent dry bias (–21 %). Over the ocean, both ERAInt and CMORPH have a small wet bias (+8 %) while the wet bias in WRF is significantly larger (+47 %). ERAInt has the highest frequency of low-intensity precipitation while the frequency of high-intensity precipitation is the lowest due to its lower native resolution. Both satellite-derived datasets have more low-intensity precipitation over the ocean than over the land, while the frequency of higher-intensity precipitation is similar or larger over the land. This result is likely related to orography, which triggers more intense convective precipitation, while the Atlantic Ocean is characterized by more homogenous large-scale precipitation systems which are associated with larger areas of lower intensity precipitation. However, this is not observed in ERAInt and WRF, indicating the insufficient representation of convective processes in the models. Finally, the Fraction Skill Score confirmed that both models perform better over the Atlantic Ocean with ERAInt outperforming the WRF at low thresholds and WRF outperforming ERAInt at higher thresholds. The diurnal cycle is simulated better in the WRF simulation than in ERAInt, although WRF could not reproduce well the amplitude of the diurnal cycle. While the evaluation of the WRF model confirms earlier findings related to the model’s wet bias over European land, the applied satellite-derived precipitation datasets revealed differences between the land and ocean areas along with uncertainties in the observation datasets.
Part of precipitation is intercepted by forest canopies, while the rest reaches the ground as throughfall or stemflow. This process is influenced by various meteorological variables, of which we have ...mainly focused on drop diameter and velocity. Rainfall in the open and throughfall under birch and pine trees have both been measured since 2014 in Ljubljana, Slovenia. The results demonstrate that the total throughfall during 3.5 years was 73% and 53% of rainfall under birch and pine trees, respectively. During the 236 analysed events, the median volume diameter was 1.8 mm (±1.7 mm), and kinetic energy between 0.01 mJ/cm2 and 23.3 mJ/cm2 was recorded. We closely analysed the effect of rainfall microstructure on throughfall under pine and birch trees during three specific rainfall events. The increase in drop diameter and fall velocity during a rainfall event instantaneously increased throughfall under pine trees between 25% and 47%, whereas no such changes were observed under birch trees. This may be the consequence of different tree properties of the two species. Additionally, in the case of a saturated canopy, throughfall under pine trees exceeded rainfall in the open after an onset of larger and faster drops.
The contribution raises a question of how good is the standard method for estimating the diffuse irradiation on a tilted surface. This is done with a correction of the diffuse irradiation measurement ...by a sky-view factor. Many different expressions for the sky-view factor can be found in the literature. According to their definitions, the sky-view factor represents the solid angle of the visible celestial hemisphere normalised by the solid angle of whole celestial hemisphere. It considers only a geometrical aspect of the available sky radiation but does not consider the amount of received irradiation in the proper way. To overcome this deficiency, the diffuse irradiation of the horizontal receiving surface (being normally measured) should be multiplied with the proposed diffuse tilt factor to obtain the irradiation of the tilted surface. Besides the orientation of the tilted surface, the diffuse tilt factor depends on ground reflectivity and the ratio between the diffuse and global irradiation of the horizontal surface.
► Sky-view factor is usually used to correct measured diffuse irradiation on a slope. ► The proposed diffuse tilt factor (DTF) is a more appropriate correction. ► DTF is based on to the slope projected radiance from the sky and the ground.
A high ozone (O3) concentrations episode during a heat wave event in the Northeastern Mediterranean was investigated using the WRF/Chem model. To understand the major model uncertainties and errors ...as well as the impacts of model inputs on the model accuracy, an ensemble modelling experiment was conducted. The 51-member ensemble was designed by varying model physics parameterization options (PBL schemes with different surface layer and land-surface modules, and radiation schemes); chemical initial and boundary conditions; anthropogenic and biogenic emission inputs; and model domain setup and resolution. The main impacts of the geographical and emission characteristics of three distinct regions (suburban Mediterranean, continental urban, and continental rural) on the model accuracy and O3 predictions were investigated. In spite of the large ensemble set size, the model generally failed to simulate the extremes; however, as expected from probabilistic forecasting the ensemble spread improved results with respect to extremes compared to the reference run. Noticeable model nighttime overestimations at the Mediterranean and some urban and rural sites can be explained by too strong simulated winds, which reduce the impact of dry deposition and O3 titration in the near surface layers during the nighttime. Another possible explanation could be inaccuracies in the chemical mechanisms, which are suggested also by model insensitivity to variations in the nitrogen oxides (NOx) and volatile organic compounds (VOC) emissions. Major impact factors for underestimations of the daytime O3 maxima at the Mediterranean and some rural sites include overestimation of the PBL depths, a lack of information on forest fires, too strong surface winds, and also possible inaccuracies in biogenic emissions. This numerical experiment with the ensemble runs also provided guidance on an optimum model setup and input data.
•Comprehensive WRF/Chem modeling with 51 ensemble members was conducted.•High O3 concentration episode in the Northern Adriatic area was studied.•Revealed the impacts of the physical schemes and model setup on the simulated O3.•The highest uncertainty found for the selection of PBL, LSM and SL schemes.•Varying emissions and radiation schemes did not significantly affect simulated O3.
The Method for Object-based Diagnostic Evaluation (MODE) developed by Davis et al. is implemented and extended to characterize the temporal behavior of objects and to perform a diagnostic analysis on ...the spatial distribution and properties of precipitation systems over the equatorial Pacific Ocean. The analysis is performed on two satellite-derived datasets Tropical Rainfall Measuring Mission (TRMM) 3B42 and Precipitation Estimation from Remotely Sensed Information using Artificial Neural Networks (PERSIANN). A sensitivity analysis showed that temporal convolution produces an unwanted "spillover" effect and that a large spatial convolution radius produces too much smoothing, which results in unrealistically large objects. The analysis showed that the largest and most long-lived precipitation systems in the tropical Pacific are typically located in the western part. A good ability to track precipitation systems in the tropical Pacific was demonstrated: movement of precipitation systems in the ITCZ is both westward and eastward although westward movement is more frequent and in the eastern part of the Pacific ITCZ the westward movement is dominant. Movement of systems in the midlatitudes was predominantly eastward. These findings were common to both satellite products, despite the fact that the average rainfall accumulation can differ by 20%-30% and the occurrence of systems with long life spans can differ by 20%. PUBLICATION ABSTRACT
An extended version of the Method for Object-based Diagnostic Evaluation (MODE) was used to perform a verification of precipitation provided by the Weather Research and Forecasting (WRF) model ...Tropical Channel Simulation (performed by NCAR). Model 3-hourly precipitation accumulations were compared to the Tropical Rainfall Measuring Mission (TRMM) 3B42 satellite-derived precipitation in the low- and midlatitude Pacific Ocean during 1998-2000. Overall, the spatial distribution of annual mean precipitation (i.e., the clear shape of the ITCZ with two maxima--one located in the east and one in the west) was reproduced well by the WRF model; however, there was considerably more precipitation in the WRF simulation than in the TRMM dataset. Object-based analysis identified more precipitation objects with life spans less than 30 h and fewer objects with life spans longer than 60 h in the TRMM dataset compared to the WRF simulation. Objects with the longest life span (>90 h) tended to occur in similar regions in both the modeled and satellite-derived datasets. Two of these regions were in the western part of the domain and one was in the eastern portion of the ITCZ, although these regions did not necessarily coincide with the regions of maximum precipitation accumulations. Both datasets had mostly eastward movement in the midlatitudes. The datasets, however, diverged around the central part of the ITCZ where the TRMM dataset displayed both eastward and westward movement, while westward movement was dominant in the WRF simulation. The analysis also showed that precipitation object trajectories were smoother in the model than in the TRMM dataset.
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