Variation Of Rain Rate Research Articles

Mean diurnal cycle of monsoon precipitation: Unified model NCUM

It is an essential component of the operational weather forecast agencies to capture the diurnal behavior of the rainfall on the spatiotemporal scale by numerical models for its accurate prediction. In this study, the mean diurnal cycle of precipitation is investigated with (i) atmospheric model-based predictions, (ii) space-based estimates, and (iii) ground-based rainfall observations during the active phase of Indian monsoon. Further, high-resolution precipitation data are used to identify the characteristics features of the model forecasts. The variability of mean diurnal variations in rain rate and frequency of rain is analyzed to determine the characteristics feature of precipitation. It is found that precipitation activity over Western Ghats, Bay of Bengal regions, is maximum during late afternoon. The time of peak rain rate is advanced during day time. The active phase of monsoon has the highest amplitude of diurnal variation in precipitation. The variability in the specific humidity is increased during this active period. The numbers of rainy hours are highly varying in nature for the space-based rainfall estimation than the model.

A 10-Year Austral Summer Climatology of Observed and Modeled Intraseasonal, Mesoscale, and Diurnal Variations over the Maritime Continent

Abstract The Maritime Continent is one of the wettest regions on the planet and has been shown to be important for global budgets of heat and moisture. Convection in the region, however, varies on several interrelated scales, making it difficult to quantify the precipitation climate and understand the key processes. For example, the diurnal cycle in precipitation over the land varies substantially according to the phase of the Madden–Julian oscillation (MJO), and the diurnal precipitation cycle over the water is coupled to that over the land, in some cases for distances of over 1000 km from the coast. Here, a 10-yr austral summer climatology of diurnal and MJO-scale variations in rain rate over the land and sea over the Maritime Continent is presented. The climatology is based on mesoscale model simulations with a horizontal grid length of 4 km and satellite precipitation estimates. The amplitude of the observed diurnal precipitation cycle is shown to reach a maximum just prior to the MJO active phase, with a weaker secondary maximum after the MJO active phase. Although these two maxima also exist in the modeled diurnal precipitation cycle, there is less difference between the maxima before and after the MJO active phase than in the observations. The modeled sea-breeze circulation is also shown to possess approximately equal maxima just before and just after the MJO active period, suggesting that the asymmetry of the diurnal precipitation cycle about the MJO active period is related more to moisture availability than kinematic forcing.

Analysis of the Effects of Rainfall Intensity into the Performance of Video Conferencing

Attenuation due to rain is an important limitation in the designing of the microwave communication links operating at frequencies above 10 GHz. Video conferencing performs over high-speed link via high-speed satellite (WINDS satellite) transmission in the Ka-band which is vulnerable to attenuation due to rain. Using the ITU-R proposed models for the prediction of rain attenuation gives a good estimation for the microwave propagation loss caused by rain for the temperate regions, but it underestimates the rain attenuation prediction for the monthly variation of rain rate by averaging annual rain rate for particular region. This study was carried out at the University of Rwanda/Huye Campus. The rain rates were predicted for 0.01 percentage of time from rainfall data measured during two months of July and August using the RD-80 Joss and Waldvogel Disdrometer. From the data collected and analyzed, compared with ITU-R model, we can see that where Rwanda region is situated in region K, what is different from the obtained results because the data are collected during months that coincide with a dry season.

Diurnal variation in summer precipitation over the central Tibetan Plateau

The diurnal cycle of rainfall over the central Tibetan Plateau was investigated by examining data acquired by the Tropical Rainfall Measuring Mission Precipitation Radar during the summer monsoon season (June–August) from 1998–2007. High‐spatial‐resolution data (∼5 km × 5 km) were used to identify the role of complex topographic features of the plateau. Diurnal variations in rain rate, frequency of rain, conditional rain rate, and storm‐height were analyzed on a monthly basis to determine the characteristics of precipitation. The results are interpreted as precipitation characteristics in a semiarid region with weak prevailing winds. Distinct diurnal variation was seen over hilly regions, valleys, and lakes. Precipitation activity over the hilly region is generally strongest during the late afternoon. But in contrast, valleys and lakes show dominant late‐evening peaks, and a secondary morning rainfall peak is distinctly evident over large lakes. However, the time of peak rain rate is delayed with increasing lake size. The shift in rain peak location toward lakes and valleys also appeared clearly.

A Climatology Model for Forecasting Typhoon Rainfall in Taiwan

The continuous torrential rain associated with a typhoon often caused flood, landslide or debris flow, leading to serious damages to Taiwan. Thus, a usable scheme to forecast rainfall amount during a typhoon period is highly desired. An analysis using hourly rainfall amounts taken at 371 stations during 1989–2001 showed that the topographical lifting of typhoon circulation played an important role in producing heavier rainfall. A climatology model for typhoon rainfall, which considered the topographical lifting and the variations of rain rate with radius was then developed. The model could provide hourly rainfall at any station or any river basin for a given typhoon center. The cumulative rainfall along the forecasted typhoon track was also available. The results showed that the R2 value between the model estimated and the observed cumulative rainfall during the typhoon period for the Dan-Shui (DSH) and Kao-Ping (KPS) River Basins reached 0.70 and 0.81, respectively. The R2 values decreased slightly to 0.69 and 0.73 if individual stations were considered. However, the values decreased significantly to 0.40 and 0.51 for 3-hourly rainfalls, indicating the strong influence of the transient features in producing the heavier rainfall. In addition, the climatology model can only provide the average conditions. The characteristics in individual typhoons should be considered when applying the model in real-time operation. For example, the model could give reasonable cumulative rainfall amount at DSH before Nakri (2002) made landfall on Taiwan, but overestimated the rainfall after Nakri made landfall and weakened with significant reduction in convection.

Evaluation of global and CCIR models for estimation of rain rate statistics

The prediction of the statistics of attenuation by rain on a radio wave propagation path requires first the prediction of rain rate statistics for a point on the path and then the conditional prediction of the path‐averaged attenuation, given the rain rate statistics. In this paper, two models with worldwide applicability, the Global and CCIR models for effecting the first step of the prediction process, are evaluated by comparing model predictions with rain rate measurements. The use of single‐year, measured rain rate statistics as a model for the prediction of the statistics for subsequent years is also evaluated. Surface rain rate distributions for one or more years of observatins at 52 locations were employed for the model evaluations. On the basis of the available data the Global model performed best. The location‐to‐location variations in rain rate at specified probability levels and in probability at specified rain rate levels were found to be well described by lognormal distributions. No significant differences were found between year‐to‐year and location‐to‐location variability estimates relative to the two rain rate prediction models. The data show that the climate models are equivalent to inference from limited‐duration records and suggest that prediction variability can be reduced by subdivision of the rain climate zones into smaller regions.