No abstract

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%.

No abstract

A B S T R A C TThe mesoscale numerical weather prediction model ALADIN has been applied for downscaling ERA40 data onto a 10 km grid covering the complex terrain of Slovenia. The modelled wind field is compared with the time-series of observations at 11 stations. In addition to traditional scores (root-mean-square error, mean absolute error, anomaly correlation), a frequency-domain comparison is carried out in order to explore aspects of the mesoscale model performance other than that depicted by the conventional statistics. The verification period is the Special Observing Period of the Mesoscale Alpine Program (MAP-SOP), for which ECMWF reanalyses including MAP-SOP observations are available every 3 hr on a ∼40 km grid.Traditional scores indicate that the downscaling has been successful. Scores are little dependent on the nesting strategy (direct versus two-step nesting), in spite of a ratio of horizontal resolutions between ERA40 and ALADIN as large as 12. The model performs best at mountaintop stations, characterized by over 80% of their spectral power in motions with longer than diurnal periods. A majority of stations is, however, located in the complex terrain where around 40% of the spectral wind power is contained in the subdiurnal frequency range. This part of the spectrum is significantly underestimated by the model, indicating that the downscaling is predominantly a dynamical adjustment to the new terrain. At the same time, the MAP-SOP reanalyses of the ECMWF model include relatively more power in the subdiurnal frequency range than ALADIN. However, these subdiurnal oscillations do not agree with observations and their removal improves conventional scores for the MAP-SOP wind data.It is suggested that a frequency-domain comparison is a useful complement to the conventional statistics and it enables a more physical insight into a mesoscale model performance.

Abstract: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/cm 2 and 23.3 mJ/cm 2 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.