Accumulated Rainfall Amount Research Articles

Statistical characteristics of raindrop size distributions observed in East China during the Asian summer monsoon season using 2‐D video disdrometer and Micro Rain Radar data

AbstractThe characteristics of raindrop size distributions (DSDs) and vertical structures of rainfall during the Asian summer monsoon season in East China are studied using measurements from a ground‐based two‐dimensional video disdrometer (2DVD) and a vertically pointing Micro Rain Radar (MRR). Based on rainfall intensity and vertical structure of radar reflectivity, the observed rainfall is classified into convective, stratiform, and shallow precipitation types. Among them, shallow precipitation has previously been ignored or treated as outliers due to limitations in traditional surface measurements. Using advanced instruments of 2DVD and MRR, the characteristics of shallow precipitation are quantified. Furthermore, summer rainfall in the study region is found to consist mainly of stratiform rain in terms of frequency of occurrence but is dominated by convective rain in terms of accumulated rainfall amount. Further separation of the summer season into time periods before, during, and after the Meiyu season reveals that intrasummer variation of DSDs is mainly due to changes in percentage occurrence of the three precipitation types, while the characteristics of each type remain largely unchanged throughout the summer. Overall, higher raindrop concentrations and smaller diameters are found compared to monsoon precipitation at other locations in Asia. Higher local aerosol concentration is speculated to be the cause. Finally, rainfall estimation relationships using polarimetric radar measurements are derived and discussed. These new relationships agree well with rain gauge measurements and are more accurate than traditional relations, especially at high and low rain rates.

The Impacts of Topography on Spatial and Temporal Rainfall Distribution over Rwanda Based on WRF Model

The impact of topography on heavy rainfall during two rain seasons was investigated in order to explain their mechanisms on rainfall distribution over Rwanda. Weather Research and Forecasting (WRF-ARW) model was used to study two historical cases of heavy rainfall which took place over Rwanda during two rain seasons, March to May (MAM) and September to December (SOND), from April 7 to 9, 2012 (for MAM) and from October 29 to 31, 2012 (during SOND). The control experiment was done with actual topography, whereas sensitivity experiment was carried out with topography reduced by half. Results show that rainfall distribution over Rwanda significantly changes when topography is reduced. The reduction in topography leads to a decrease in rainfall amounts in both MAM and SOND seasons, with varying magnitudes. This reveals the importance of orography in determining rainfall amounts and distribution over the region. The accumulated rainfall amount from WRF underestimate or overestimate rain gauge stations data by region and by season, but there is good agreement especially in altitude below 1490 m and above 1554 m during April and October respectively. The results may motivate modelling carters to further improve parameterization schemes in the mountainous regions.

The web‐based accumulated rainfall amount monitoring system by X‐band MP radar

AbstractFlood damage due to heavy rain is quite severe in Japan during the annual typhoon season, which causes death and serious destruction every year. Moreover, serious damage (flood damage and landslide disaster, etc.) by localised torrential rains and local heavy rains has increased in Japan in recent years. The Ministry of Land, Infrastructure, Transport and Tourism of Japan started the operation of an X‐band Multi‐Parameter (MP) radar system in February 2012, at 23 observation stations in Japan. Rainfall observations by the X‐band MP radar system are more detailed than by the past C‐band radar. However, now, applications of X‐band MP radar data are mostly only for displaying 1‐min rainfall images. The Japan Meteorological Agency is providing a standard of the rain situation (strength of rain), which shows hazard levels of the rainfall amount in 1 h. Those hazard levels of the accumulated rainfall amount are quite important to estimate disaster events. Thus, in the present study, an accumulated rainfall amount monitoring system is developed. The accumulated rainfall amount can be clearly shown on a PC monitor or a mobile terminal monitor. It takes up to 5 min to show the results on the web site after having observed rainfall in 1 h. It was shown that this is an effective system for local governments, etc. to monitor rainfall amount information, and to give flood warnings and evacuation orders to residents in the vicinity.

Numerical simulation of the heavy rainfall caused by a convection band over Korea: a case study on the comparison of WRF and CReSS

This study investigates the capability of two numerical models, namely the Weather Research and Forecasting (WRF) and Cloud Resolving Storm Simulator (CReSS), to simulate the heavy rainfall that occurred on September 21, 2010 in the middle of the Korean peninsula. This event was considered part of the typical rainfall caused by intense quasi-stationary convection band, leading to a large accumulated rainfall amount within a narrow area. To investigate the relevant characteristics of this heavy rainfall and the feasibility of the numerical models to simulate them, the experiments using both numerical models were designed with a focus on Korea with a horizontal grid spacing of 2 km. The initial and later boundary conditions were interpolated using the output of the mesoscale model of Japan Meteorological Agency and integration spanned the 24-h period from 2100 UTC on September 20, 2010 when the rainfall started in the Yellow Sea. Generally, the spatial distribution and temporal evolution of the rainfall simulated by CReSS are closer than those of the WRF to the in situ observations (655 stations). The WRF simulation reveals the deficiency in capturing the unusual stagnant behavior of this event. The spatial and vertical patterns of reflectivity are consistent with the rainfall pattern, supporting that strong reflectivity coincides with the convective activity that accompanies excessive rainfall. The thermodynamic structure is the main driver of the different behavior between both simulations. The higher equivalent potential temperature, deep moist absolutely unstable layer and strong veering wind shear seen in the CReSS simulation play a role in the development of a favorable environment for inducing convection.

Laboratory-Based Rainfall Effects on LWIR Soil Reflectance

The long-wave infrared reflectance of in situ disturbed and undisturbed soils will often have distinct spectral characteristics that are dependent on the soil's physical and spectral constitutive properties. This study examines how rainfall alters the measured directional-hemispherical thermal infrared (8-14 μm) spectral reflectance of a disturbed soil with a specified sand/silt ratio using a calibrated rainfall simulator. For an accumulated rainfall of 8.0 cm, the mean disturbed soil thermal infrared spectral reflectance within 8.1-9.2-μm waveband increases from an initial reflectance of 13% to a maximum reflectance of 31 %. Sixty percent of this reflectance change occurred with only 1.0-cm accumulated rainfall. This study shows that, for this described disturbed sand/silt soil mixture, small accumulated rainfall amounts significantly alter the directional-hemispherical thermal infrared spectral reflectance.

앙상블 민감도를 이용한 2003년 8월 6일 집중 호우 역학 분석

Ensemble sensitivity has been recently proposed as a method to analyze the dynamics of severe weather events. We adopt it to investigate the physical mechanism which caused the heavy rainfall over the Korean Peninsula on 6th August 2003. Two rainfall peaks existed in this severe weather event. The selected response functions are 1 hour accumulated rainfall amount of each rainfall peak. Sensitivity fields were calculated using 36 ensemble members which were generated by WRFDA. The sensitive regions for the first rainfall peak are located over the Shandong Peninsula and the Yellow Sea at 12 hours before the first rainfall peak. However, the 12-h forecast sensitivity for the second rainfall peak is revealed near Typhoon ETAU (0310) and midlatitude trough. These results show that the first rainfall peak was induced by low pressure which located over the northern part of the Korean Peninsula while the second rainfall peak was caused by the interaction between typhoon ETAU and midlatitude trough.

Forecast models and trends for the main characteristics of the Olea pollen season in Nice (south-eastern France) over the 1990–2009 period

The olive tree, Olea europaea, is very common in the southeast of France and its pollen is recognised as one of the most important allergenic in the Mediterranean. This study allowed for the development of predictive models to calculate the main characteristics of the Olea pollen season over the last 20 years from a wide range of meteorological variables. Clear evidence of the relationship between the main features of the Olea pollen season and the temperature recorded during the months before the flowering period could be demonstrated. The mean temperature in February plays an important role in determining reproductive growth and anthesis. It seems that the mean temperature during autumn influences the pollen index of the next year's pollen season. Other environmental factors, such as global radiation and rainfall, may be of great influence in determining the onset and final date of pollination. The accumulated rainfall amount during the pollination period has a negative effect on the pollen index. This may be interpreted as the wash out of airborne pollen by raindrops. However, rainfall during the vegetative period has a positive effect on pollen production. The pollen quantities depend not only on meteorological conditions before pollen release, but also maybe on those prevailing during pollen release. Finally, we could demonstrate an upward trend in annual pollen production and a stability of the mean duration of the Olea pollen season. The increase in Olea pollen abundance coincides with a rise in air temperature over the last 20 years.

Multiplatform Comparisons of Rain Intensity for Extreme Precipitation Events

Rainfall intensities during heavy rain events over the continental U.S. are compared for several advanced radar products. These products include the following: 1) Tropical Rainfall Measuring Mission (TRMM) precipitation radar (PR) near-surface estimates; 2) NOAA Quantitative Precipitation Estimation very high resolution (1 km, instantaneous) radar-only national mosaics (Q2); 3) very high resolution gauge-adjusted radar national mosaics, which we have developed by applying a gauge correction on the Q2 products; and 4) several independent C-band dual-polarimetric radar-estimated rainfall samples collected with the Advanced C-band Radar for Meteorological and Operational Research (ARMOR) radar in Alabama. These instantaneous rainfall rate fields [i.e., 1)-3)] can be considered as radar products with the largest coverage currently available from space- and ground-based radar observations. Although accumulated rainfall amounts are often similar, we find the PR and Q2 rain-rate histograms quite different. PR rain-rate histograms are shifted toward lower rain rates, implying a much larger stratiform/convective rain ratio than do products such as Q2. The shift is more evident during strong continental convective storms and not as pronounced in tropical rain. A “continental/maritime regime” behavior is also observed upon adjusting the Q2 products to rain gauges, yet the rain amount more closely agrees with that of PR. The independent PR/ARMOR comparisons confirm this systematic regime behavior. In addition, comparisons are performed over central Florida where PR, Q2, and the NASA TRMM ground validation products are available. These comparisons show large discrepancies among all three products. Resolving the large discrepancies between the products presents an important set of challenges related to improving remote-sensing estimates of precipitation in general and during extreme events in particular.

The Impacts of Taiwan Topography on the Predictability of Typhoon Morakot’s Record-Breaking Rainfall: A High-Resolution Ensemble Simulation

Abstract In this study, the impacts of Taiwan topography on the extreme rainfall of Typhoon Morakot and the predictability of this rainfall are examined with a high-resolution (4 km) ensemble simulation using the Advanced Research core of the Weather Research and Forecasting Model (WRF-ARW). Ensemble prediction with realistic topography reproduces salient features of orographic precipitation. The 24- and 96-h accumulated rainfall amount and distribution from the ensemble mean compare reasonably well with the observed precipitation. When the terrain of Taiwan is removed, the rainfall distribution is markedly changed, suggesting the importance of the orography in determining the rainfall structure. Moreover, the peak 96-h rainfall amount is reduced to less than 20%, and the total rainfall amount over southern Taiwan is reduced to less than 60% of the experiments with Taiwan topography. Further analysis indicates that Taiwan’s topography substantially increases the variability of rainfall prediction. Analysis uncertainties as reflected in the perturbed initial state of the ensemble are amplified due to orographic influences on the typhoon circulation. As a result, significant variability occurs in the storm track, timing, and location of landfall, and storm intensities, which in turn, increases the rainfall variability. These results suggest that accurate prediction of heavy precipitation at a specific location and at high temporal resolution for an event such as Typhoon Morakot over Taiwan is extremely challenging. The forecasting of such an event would benefit from probabilistic prediction provided by a high-resolution mesoscale ensemble forecast system.

Features of the Indian Summer Monsoon 2004-Observed and Model Forecasts

The observed and the model forecast rainfall and other atmospheric fields are compared to determine the skill of the National Centre for Medium Range Weather Forecasting (NCMRWF) model in forecasting precipitation and circulation features over India, we compared observed and forecast rainfall and other atmospheric fields for the boreal summer monsoon season of 2004. This season was an important period within the period 4 of the Coordinated Enhanced Observing Period (CEOP). For comparison of observed rainfall with predicted values, station values are averaged over the area represented by each grid point of the model. For other fields, comparisons were made between the analysis and forecast values at the same horizontal resolution. The model showed considerable skill in predicting the daily and seasonal accumulated rainfall amounts when averaged over the whole of India. The predicted all-India average precipitation tends to increase in magnitude with increasing forecast period. The model forecasts that were undertaken especially for the CEOP project reproduced the important features of the summer monsoon over India. The onset of monsoon is captured in terms of both the convective precipitation and diabatic heating fields forecast by the model. Variations in monsoon activity between July and August are also well simulated in the monthly averaged forecast fields for these two months.

Effect of rainfall intensity and distribution on groundwater level fluctuations

A mathematical equation describing the relationship between the groundwater level increment and the effective accumulated rainfall amount is proposed in this study. The groundwater level measurements were taken from the Donher well station in Central Taiwan and the rainfall data were collected from seven rain-gauge stations nearby the well station. To analyze the relationship, we first employed the BAYTAP-G program to filter out the response of the groundwater level to non-rainfall effects, such as barometric pressure and earth tide. Because both the present and antecedent rainfall events give an impact on the groundwater level increment, an effective accumulated rainfall amount was defined to account for their influences using the exponential-decay weighting method. The resulting groundwater level, conventionally termed the residual groundwater level, was found to linearly depend on the effective accumulated rainfall amount. It was also shown that the effective accumulated rainfall amount calculated from the exponential-decay weighting method with a decay parameter of 0.25 reveals a highly-correlated relation to the residual groundwater level increment. Lastly, we demonstrated that rainfall occurring beyond the surface watershed within which the Donher well station locates indeed affects the residual groundwater level. The effect can be incorporated into our proposed equation.

STUDY ON DEPENDENCE PROPERTIES OF RAINFALL DISTRIBUTIONS ON TOPOGRAPHY CONSIDERING THE THREE DIMENSIONAL STRUCTURE AND TYPES OF RAINFALL

The purpose of this study is to analyze the relation between rainfall distribution and topography using three dimensional rainfall information of weather radar. By analyzing the distributions of three indexes of accumulated rainfall amount, accumulated rainfall time and average rainfall intensity, it is made clear how the mechanism of topographic effects on rainfall distributions is different between the types of rainfall, stratiform rainfall and convective rainfall. Additionally the three dimensional properties of topographic effects are quantified using Dependence Line on Topographic Elevations (DLTE), which represents dependence properties of rainfall distribution on topographic elevation.

Numerical Simulations with MM5 3DVAR Initialization

The recently developed MM5 three-dimensional variational (3DVAR) assimilation system at NCAR has been used to investigate influences of ingested sounding and ship observation data on numerical simulations of severe weather in the vicinity of Taiwan. Three weather events were simulated in this study, which include a Mei-Yu front in June 1998, Supertyphoon Bilis in August 2000 and Typhoon Nari in September 2001. For the Mei-Yu front, the simulated low-pressure system northeast of Taiwan is stronger. when the 3DVAR is performed during initialization. The simulated patterns of heavy rainfall just off the southern tip of Taiwan are also closer to observations for the run with 3DV AR. For the second case of Typhoon Bilis, both runs with and without 3DVAR show a northward bias in track upstream of eastern Taiwan. However, due to less northward track deflection, the simulated heavy rainfall in Taiwan for the 3DV AR run is in better agreement with observations. For the no-3DVAR run, the simulated Typhoon Nari consistently moves southwestward toward Taiwan but then makes an incorrect landfall at northwestern Taiwan. With 3DVAR, the track simulation is improved with a landfall position at northeastern Taiwan. During landfall, the associated could convection is enhanced as the intense vortex core is in confrontation with the leading edge of the Central Mountain Range (CMR) and its movement is slowed down along the northwestern coast. The combination of both compression and stagnation of the embedded convective system may explain the extremely intense rainfall in northern Taiwan. The feature of observed intense rainfall over the southwestern slope base of the C／MR is also captured, but the intensity is considerably underpredicted due to lagging and weakening of the vortex core at later -times for both runs with and without 30V AR. The track simulation at later times has also been improved in the 3DVAR run, but the associated geometric distributions of 72h accumulated rainfall amounts in general are similar to those without 3DVAR. In the typhoon experiment with a bogus vortex, the 3DVAR rum preserves the initial vortex, quite well. However, the rainfall and track simulations are not improved by the ingestion of the bogus vortex for both runs with and without 3DVAR.

Temporal modelling of short-term rainfall using Cox processes

We study two marked point process models based on the Cox process. These models are used to describe the probabilistic structure of the rainfall intensity process. Mathematical formulation of the models is described and some second-moment characteristics of the rainfall depth, and aggregated processes are considered. The derived second-order properties of the accumulated rainfall amounts at different levels of aggregation are used in order to examine the model fit. A brief data analysis is presented. Copyright © 1998 John Wiley & Sons, Ltd.

Temporal modelling of short‐term rainfall using Cox processes

We study two marked point process models based on the Cox process. These models are used to describe the probabilistic structure of the rainfall intensity process. Mathematical formulation of the models is described and some second-moment characteristics of the rainfall depth, and aggregated processes are considered. The derived second-order properties of the accumulated rainfall amounts at different levels of aggregation are used in order to examine the model fit. A brief data analysis is presented. Copyright © 1998 John Wiley & Sons, Ltd.

Comparison of Raindrop Size Distribution Measurements by a Joss-Waldvogel Disdrometer, a PMS 2DG Spectrometer, and a POSS Doppler Radar

Abstract Three techniques for the measurement of raindrop size distributions are compared using data from a Joss-Waldvogel disdrometer (JWD), a Particle Measuring Systems 2DG spectrometer (PMS), and an Atmospheric Environment Service (AES) Precipitation Occurrence Sensor System (POSS). The techniques used are impact measurement by the JWD, optical imaging by the PMS, and Doppler velocity spectrum by the POSS. The sampling size errors arc compared. The effects of both vertical and horizontal winds on the measurements are evaluated. Accumulated rainfall amounts derived from the drop size distributions (DSDs) are compared to measurements by conventional gauges at the radar facility of AES at King City, Ontario, Canada. In general, DSDs and rain rates averaged for 1 min were in agreement between the three sensors While 1-min-averdged DSDs were multimodal, long-time-period averages followed the Marshall-Palmer distribution.