Speed Of Raindrops Research Articles

Comparisons of Rainfall Microphysical Characteristics between the Southeastern Tibetan Plateau and Low-Altitude Areas

Abstract The low air pressure and density over the Tibetan Plateau may have an impact on the microphysical features of rainfall. Using a two-dimensional video disdrometer (2DVD), a Micro Rain Radar (MRR), and a microwave radiometer (MWR), the features of the raindrop size distribution (DSD) on the southeastern Tibetan Plateau (SETP) are explored and compared with those in low-altitude regions. The falling speed of raindrops on the SETP is higher than that in low-altitude areas. Under different rainfall-rate categories, the number concentration and the maximum diameter of raindrops on the SETP are smaller than those in low-altitude regions. The convective rainfall on the SETP is more maritime-like because the South Asian summer monsoon brings water vapor from the ocean here. For stratiform and convective rainfall, the SETP has more small-sized raindrops than low-altitude locations. The mass-weighted mean diameters (Dm) on the SETP are the smallest among six sites. The generalized intercept parameter (Nw) of stratiform rainfall is balanced at a low rainfall rate, while that of convective rainfall is balanced at a high rainfall rate. Furthermore, for a given μ (the shape parameter of gamma distribution) value, the λ (the slope parameter of gamma distribution) value on the SETP is the highest of the six sites. Significance Statement For the occurrence and progression of rainfall, microphysical processes (for instance, collision, fragmentation, coalescence, and evaporation) that take place when rainfall particles descend are crucial. A key factor in the microphysical features of rainfall that varies with rainfall rates and types is the raindrop size distribution (DSD). The southeastern Tibetan Plateau (SETP)’s unique terrain ensures that there is enough moisture for rain to fall there, but little is known about the microphysical aspects of this type of precipitation. There has not been enough research done on how the high altitude affects the microphysical features of rainfall. The microphysical features of rainfall in this area must thus be studied.

Wind and Turbulence Effects on Raindrop Fall Speed

Abstract Wind and turbulence effects on raindrop fall speeds were elucidated using field observations over a 2-yr time period. Motivations for this study include the recent observations of raindrop fall speed deviations from the terminal fall speed predictions (Vt) based upon laboratory studies and the utilizations of these predictions in various important meteorological and hydrological applications. Fall speed (Vf) and other characteristics of raindrops were observed using a high-speed optical disdrometer (HOD), and various rainfall and wind characteristics were observed using a 3D ultrasonic anemometer, a laser-type disdrometer, and rain gauges. A total of 26 951 raindrops were observed during 17 different rainfall events, and of these observed raindrops, 18.5% had a subterminal fall speed (i.e., 0.85Vt ≥ Vf) and 9.5% had a superterminal fall speed (i.e., 1.15Vt ≤ Vf). Our observations showed that distributions of sub- and superterminal raindrops in the raindrop size spectrum are distinct, and different physical processes are responsible for the occurrence of each. Vertical wind speed, wind shear, and turbulence were identified as the important factors, the latter two being the dominant ones, for the observed fall speed deviations. Turbulence and wind shear had competing effects on raindrop fall. Raindrops of different sizes showed different responses to turbulence, indicating multiscale interactions between raindrop fall and turbulence. With increasing turbulence levels, while the raindrops in the smaller end of the size spectrum showed fall speed enhancements, those in the larger end of the size spectrum showed fall speed reductions. The effect of wind shear was to enhance the raindrop fall speed toward a superterminal fall.

Effects of anthropogenic and sea salt aerosols on a heavy rainfall event during the early-summer rainy season over coastal Southern China

Effects of anthropogenic and sea salt aerosols (AA and SSA, respectively) on heavy rainfall in the densely populated monsoon coastal areas remain poorly known. To address this issue, a representative heavy rainfall event over coastal Southern China is simulated using the Weather Research and Forecasting model coupled to Chemistry (WRF-Chem). Results show that the initial responses of clouds to AA and SSA are opposite due to their different size distributions: increasing the AA emission by tenfold leads to larger mixing ratio and number concentration of cloud droplets (Qc and Nc) with reduced size; on the contrary, presence of SSA results in less but larger cloud droplets as activation of smaller aerosols is inhibited on the order of 105 to 106 m−3 due to increased competition for the supersaturated water vapor between SSA and other smaller particles as cloud condensation nuclei. In the polluted environment, rain number concentration (Nr) is reduced to about a half of that in the clean environment due to weakened auto-conversion from cloud droplets to raindrops. The reduced Nr combined with enhanced accretion of cloud droplets by raindrops result in larger mean size and faster mean fall speed of raindrops, therefore probability distribution of surface hourly rain rate shifts toward values > about 2 mm h−1. The 24-h rainfall accumulation increases up to about 80 mm at the centers, although the region-averaged amount increases only 5.32%. Meanwhile, increasing the AA emission decreases total mixing ratio of ice-phase hydrometeors while the previously reported convective intensification is not evident. When the SSA emission is included in the polluted environment, the significantly inhibited activation of submicron aerosols leads to weakening of the following liquid-, mixed-, and ice-phase microphysical processes and the convective intensity to some extents. The probability distribution of hourly rain rates shifts toward values < about 5 mm h−1, while the 24-h rainfall accumulation hardly changes significantly with a decrease of 4.19% in the regionally averaged amount. The overall small impacts of aerosols, SSA in particular, are related to the strong synoptic forcing governing the heavy rainfall production in this case.

Determining the potential impacts of fire and different land uses on splash erosion in the margins of drylands

This research aimed to estimate the splash erosion and its evolution during the first months in specific land uses after a forest fire. The study area was located in Congosto (North-West Spain), in the margins of Spanish drylands, after a wildfire occurred in May 2012, which burned 15.56 ha of scrubland and Pinus reforestation. Two different burned land uses were selected and compared to control areas: i) burned pine forest; and, scrublands. Rainfall intensity and the number, sizes and speed of raindrops were measured by an optical disdrometer and soil loss by funnels. Moreover, infiltration, soil moisture content, aggregate stability, water repellence, pH and organic matter were also measured. Results showed that the highest soil losses occurred in the burned areas, especially in the scrubland plots. The most influential factors were the presence of bare soil and the low vegetation recovery rate. Changes in soil properties did not significantly influence splash erosion, although an increase in the presence of smaller classes of aggregates could promote erosion in the scrubland. We conclude that the vegetation ecosystem restoration is the key issue to be considered after a wildfire, especially, in those types of land uses which are severely affected by the fire in the margins of drylands.

Study on the rainfall change in Pisha stone area

Rainfall and raindrop characteristics have an important impact on the erosion of sandstone soil. The LPM laser raindrop spectrometer is used to analyze the rainfall characteristics of the Ordos City in the Yellow River Basin, including the distribution characteristics of the velocity and size of a natural rainfall raindrop. Statistical analysis shows that with the gradual strengthening of rainfall intensity, the number of raindrops per unit time, the size and speed of raindrops will increase parabolically. However, the natural rainfall process finds that the diameter and velocity of the raindrop are relatively scattered. During this measurement, the velocity of raindrops is mainly distributed between 1-3.4m / s, and most raindrops are distributed at 1-1.8m / s. The diameter of the raindrops is mainly distributed in the range of 0.125-0.5 mm. The raindrops with a diameter of 0.125mm are mainly distributed between 0.8-3.4m / s, the raindrops with a diameter of 0.25mm are mainly distributed between 1-2.6m / s, and the raindrops with a diameter of 0.375mm are mainly distributed between 1.0-2.2 m/s, and the diameter of 0.5 mm is mainly distributed in the range of 2.2-2.6 m / s.

Transformation of Rainfall(Aug 6,2018) characteristics in Yinchuan city

The rainfall feature were analyzed at Yinchuan city in this paper, the rainfall feature was detected by LPM laser raindrop spectrometer, including rainfall raindrops speed and raindrops size. The data shows that the rainfall raindrops speed and size of natural raindrops were relatively strongly; In the process of individual rainfall, the rainfall raindrops final speed of the rain is mainly distribution between 0.6-5.8m/s, the biggest of the final speed is generally 1.0m/s; and rainfall raindrops is mainly composed of the particle size of 0.125- 0.5mm rainfall raindrops. The rainfall raindrops speed of 0.125mm diameter is mainly distribute between 0.6-1.8m/s, the rainfall raindrops speed of 0.25mm particle size is mainly distribute between 0.8-1.8m/s, the rainfall raindrops speed of 0.375mm distribute in the 1-1.8m/s, the rainfall raindrops speed of 0.5mm particle size of the raindrops mainly distribute in the 1.0-2.2m/s.

Transformation of Rainfall(Aug 6,2018) characteristics in Yinchuan city

The rainfall feature were analyzed at Yinchuan city in this paper, the rainfall feature was detected by LPM laser raindrop spectrometer, including rainfall raindrops speed and raindrops size. The data shows that the rainfall raindrops speed and size of natural raindrops were relatively strongly; In the process of individual rainfall, the rainfall raindrops final speed of the rain is mainly distribution between 0.6-5.8m/s, the biggest of the final speed is generally 1.0m/s; and rainfall raindrops is mainly composed of the particle size of 0.125- 0.5mm rainfall raindrops. The rainfall raindrops speed of 0.125mm diameter is mainly distribute between 0.6-1.8m/s, the rainfall raindrops speed of 0.25mm particle size is mainly distribute between 0.8-1.8m/s, the rainfall raindrops speed of 0.375mm distribute in the 1-1.8m/s, the rainfall raindrops speed of 0.5mm particle size of the raindrops mainly distribute in the 1.0-2.2m/s.

Microphysical Characteristics of an Asymmetric Eyewall in Major Hurricane Harvey (2017)

AbstractMicrophysical and kinematic structures of major Hurricane Harvey's (2017) asymmetric eyewall are analyzed from ground‐based polarimetric and airborne Doppler radars. New polarimetric observations of differential reflectivity (ZDR) and specific differential phase (KDP) show asymmetric wavenumber‐1 patterns associated with vertical wind shear (VWS) but were shifted azimuthally with respect to the reflectivity (ZH) asymmetry. A ZDR column was found upwind of the ZH maximum in a region with strong updrafts estimated from multi‐Doppler synthesis, with higher values of KDP found cyclonically downwind. Retrieved raindrop size distributions show that azimuthal variations of size and number concentration were determined by both the VWS and the size sorting process. The diameter of raindrops decreases, while the number concentration increases cyclonically downwind of VWS‐induced updrafts due to the differential terminal fall speed of raindrops and strong rotational flow at major hurricane wind speeds.

Observation and Analysis of Meteorological Conditions for Icing of Wires in Guizhou, China

Icing of wires is a product of rain, fog, and freezing rain, and is a common meteorological disaster in winter in Guizhou Province of China. It is extremely harmful to facilities such as power transmission and communication lines, and has caused huge economic loss up to 48.9566 billion dollars a year. Based on the meteorological records of Guizhou from 1967, we analyze the meteorological characteristics during the icing of wires, and obtain the temperature, wind speed and direction conditions of the ice accident. The icing of wires is carried out by supercooling raindrops, freezing of the clouds, freezing and spreading on the wires. Different types of supercooled raindrops and cloud freezing and freezing processes will form different types of ice accretion; wind direction and wind speed will affect the growth of ice accretion by changing the speed of sub-cooling raindrops and cloud falling. The weight of rain-type ice accretion is between 24 and 152 g, and the weight of smog-type ice is between 40 - 76 g. The average ice density of these two places can be calculated to be 0.2 - 0.5 g/cm3. The longer the icing of wires, the higher the ice disaster rate.

Raindrop Characteristics Analysis by Laser Raindrop Spectrometer

Raindrop characteristics, including speed and size of raindrops, in Zhengzhou city of Yellow River basin were analyzed through a natural rainfall on the loess slope. Results showed that the process of natural rainfall belonged to a parabola and counts, size and terminal velocity would increase with the rainfall intensity rising. Besides, the size and terminal velocity of natural raindrops were relatively scattered; In the process of individual rainfall, the terminal velocity and its peak value were mainly focused between 1∼4.2m/s and 1.4-3.4m/s, respectively. Size of raindrops were mainly consisted of 0.125-0.5mm, The final velocity of 0.125mm is mainly between 1-3.4m/s, and the final velocity of the raindrops with 0.25mm particle size is mainly concentrated on the range of 1-4.2m/s, 0.375mm diameter of the raindrops mainly concentrated on the 1-3.4m/s, the 0.5mm diameter of the raindrops mainly concentrated on the 3.4-4.2m/s.

Raindrop characteristics analysis (Oct 25, 2015) of natural rainfall in Zhengzhou city of Yellow River basin

Raindrop characteristics, including speed and size of raindrops, in Zhengzhou city of Yellow River basin were analyzed through a natural rainfall on the loess slope. Results showed that the process of natural rainfall belonged to a parabola and counts, size and terminal velocity would increase with the rainfall intensity rising. Besides, the size and terminal velocity of natural raindrops were relatively scattered; In the process of individual rainfall, the terminal velocity and its peak value were mainly focused between 1∼5m/s and 3.4m/s, respectively. Size of raindrops were mainly consisted of 0.125-1.25mm, among which the terminal velocity of raindrops with a size of 0.125mm, 0.25mm, 0.375mm, 0.5mm, 0.75mm and 1mm were primarily 0.8-2.6m/s, 1-3.4m/s, 1.4-3.4m/s, 1.8-3.4m/s, 3-4.2m/s and 3.4-5m/s, respectively.

Transformation of Raindrop characteristics (Nov 24, 2015) of natural rainfall of Yellow River basin

Raindrop characteristics, including speed and size of raindrops, in Zhengzhou city of Yellow River basin were analyzed through a natural rainfall on the loess slope. Results showed that the process of natural rainfall belonged to a parabola and counts, size and terminal velocity would increase with the rainfall intensity rising. Besides, the size and terminal velocity of natural raindrops were relatively scattered; In the process of individual rainfall, the terminal velocity and its peak value were mainly focused between 1∼3.4m/s and 1.4m/s, respectively. Size of raindrops were mainly consisted of 0.125-0.75mm, among which the terminal velocity of raindrops with a size of 0.125mm, 0.25mm, 0.375mm, 0.5mm and 0.75mm were primarily 1-3.4m/s, 1-4.2m/s, 0.8-3.4m/s, 0.8-3.4m/s, 1-2.6m/s, respectively.

Analysis of day rainfall characteristics of Zhengzhou

Raindrop characteristics, including speed and size of raindrops, in Zhengzhou city of Yellow River basin were analyzed through a natural rainfall on the loess slope. Results showed that the process of natural rainfall belonged to a parabola and counts, size and terminal velocity would increase with the rainfall intensity rising. Besides, the size and terminal velocity of natural raindrops were relatively scattered; In the process of individual rainfall, the terminal velocity and its peak value were mainly focused between 0.8~5m/s and 1m/s, respectively. Size of raindrops were mainly consisted of 0.125-0.5mm, among which the terminal velocity of raindrops with a size of 0.125mm, 0.25mm, 0.375mm, 0.5mm were primarily 0.8-3.4m/s, 0.6-3.4m/s, 0.8-1m/s, 1-1.4m/s, respectively.

Study on the Raindrops Characters of 20140827 Natural Rainfall

In this paper, we adopted natural rain experiment method to study the transformation of the change of raindrop speed and diameter with time and the results indicated that the rain intensity change strongly with time at the natural rainfall. At the natural rain, the raindrop speed mainly at 0.8-5m/s in different time 20140827 natural rain, it has wave crest were 1m/s-1.4m/s. In natural rain and simulate rain, the 0.125mm diameter raindrop speed were about at 0.6-1.8m/s, the 0.25mm diameter raindrop speed were about at 1-1.8m/s, the 0.375mm diameter raindrop speed were about at 1-2.6m/s, the 0.5mm diameter raindrop speed were about at 1.8-3.4m/s, the 0.75mm diameter raindrop speed were about at 2.6-4.2m/s, the 1mm diameter raindrop speed were about at 3.4-4.2m/s, the 1.25mm diameter raindrop speed were about at 4.2-5m/s.

On the behaviour of raindrop fall speed due to wind

Measurements of raindrop fall speed gathered at the ground over several years are presented and analysed in view of the horizontal wind intensity during sampling. It is confirmed that super‐terminal drops occur only for diameters less than about 0.7 mm and that their percentage numbers increase during windy periods. Furthermore, through statistical and post hoc data analyses, it is shown that wind affects the fall speed of individual raindrops. A remarkable feature is the detection of sub‐terminal raindrops, i.e. those having slower fall speeds than their calculated terminal velocities, smaller than 2 mm. Evidence that wind affects raindrop behaviour includes observations showing that under windy conditions: (i) super‐terminal drops exhibit larger fall speed departures from the expected terminal speeds than in calm wind periods; and (ii) the percentage number of sub‐terminal drops with diameters between 1 and 2 mm increases. These two findings imply a general broadening of the corresponding velocity distributions. Potential explanations for the occurrence of sub‐terminal drops are given based on turbulence (small raindrops respond faster to changes in air conditions), drop oscillations (which produce larger transit times through the instrument sampling volume) and the enhancement of transverse drifts and trajectory deviations with respect to the vertical. However, other possibilities should be also addressed for drops with the largest fall speed anomalies (greater than two times the instrument uncertainty) as well as their implications for microphysical processes.

Transformation of the Raindrop Speed Base on Diameter about Soil Erosion Similar

Simulate rain experiment method was adopted to study the transformation of the change of raindrop speed and diameter with time and the results indicated that the rain intensity change strongly with time at the natural rainfall, However, the rain intensity was stability at simulate rainfall. At the natural rain, the raindrop speed mainly at 0.4-6.6m/s in different time, it have two wave crest were 1m/s and 3.4m/s. However, at the simulate rain, the raindrop speed mainly at 0.2-5.8m/s in different time; it has one wave crest was1m/s.In natural rain and simulate rain, the 0.125mm diameter raindrop speed were about at 0.4-2.6m/s and0.8-5.8m/s, the 0.25mm diameter raindrop speed was about at 0.6-2.6m/s and 0.6-5.8m/s, the 0.375mm diameter raindrop speed was about at 1-1.8m/s and0.4-2.2m/s, the 0.5mm diameter raindrop speed was about at 1-3.4m/s and 0.2-1.8m/s, the 0.75mm diameter raindrop speed was about at 3.4-4.2m/s and1-3.4m/s, the 1mm diameter raindrop speed was about at 3.4-4.2m/s and 1-3.4m/s, the 1.25mm diameter raindrop speed was about at4.2-5m/s and1-5m/s, the 1.5mm diameter raindrop speed was about at5m/s and 2.6m/s.

Performance of a new low‐cost laser disdrometer with rainfall intensity correction in heavy rainfall

AbstractRecently, a new low‐cost disposable laser disdrometer with the capacity for hydrometeor imaging was proposed by the authors. The laser disdrometer has the drawback of detecting false raindrops, which are splashed droplets and pooled water drops on the housing. Actual raindrops can be sorted from false raindrops by their different fall speeds, but the large size and slow falling speed of false raindrops induce significant observational dead time, affecting the raindrop capture rate and the number density of the raindrops. The ratio between the actual number of raindrops and the total number of drops including the false raindrops provides a reasonable rain intensity correction. This report describes the performance of a laser disdrometer with rain intensity correction in heavy rainfall. © 2014 Institute of Electrical Engineers of Japan. Published by John Wiley &amp; Sons, Inc.

Study on the Rainfall Similar of Soil Erosion on Loess Slope

A lot of research about soil erosion similarity have done and obtained rich achievements. However, strictly speaking, it need to do a lot of deep study about to establish the ratio scale model of soil erosion, the problems unsolved include of does not establish the similar equation system about soil erosion and sediment yield entities simulation. we did some experiment, the date shows: the raindrop speed mainly at 0.6-5m/s in 10min, the wave crest was 1m/s and 4.2m/s. At the same times, the 0.125mm grain diameter raindrop speed was about at 0.6-1.4m/s, the 0.25mm grain diameter raindrop speed was about at 1-1.4m/s, the 0.375mm grain diameter raindrop speed was about at 1-1.4m/s, the 0. 5mm grain diameter raindrop speed was about at 1-3.4m/s, the 0.75mm grain diameter raindrop speed was about at 3.4m/s, the 1mm grain diameter raindrop speed was about at 4.2m/s, the 1.25mm grain diameter raindrop speed was about at4.2-5m/s, the 1.5mm grain diameter raindrop speed was about at5m/s.

Why does radar reflectivity tend to increase downward toward the ocean surface, but decrease downward toward the land surface?

Both ground and space borne radars have shown that radar reflectivity profiles below the freezing level have different slopes over land and ocean in general. This is critical in correctly estimating the surface precipitation rate in the usual situation in which the radar reflectivity cannot be measured as close to the surface as one would like. Using 14 years of Tropical Rainfall Measuring Mission precipitation radar observations, the variations of slopes of the radar reflectivity in the low troposphere are examined over the stratiform and convective precipitation regions. Radar reflectivity below the freezing level usually decreases toward the surface over land, but increases toward the surface over the ocean. Increasing reflectivity toward the surface is hypothesized to occur mainly when raindrops grow while falling through low clouds, which is favored by high humidity at low levels, and by updraft speeds lower than the fall speed of raindrops, both more likely over oceans. Other things being equal, proxy evidence is presented that the more intense the convection, the more likely reflectivity is to decrease toward the surface, and that this is at least as important as low‐level relative humidity. Over monsoon regions with more moderate convection but higher humidity, such as southeast China and the Amazon, there are more profiles with reflectivity increasing toward the surface than over other continental regions such as Africa. Radar reflectivity tends to increase toward the surface in shallow warm rain systems in trade cumulus regions, but tends to decrease toward the surface when high reflectivity values are present at or above the freezing level.

The Research of Calibration of the Rainfall in Laboratory Landslide Test

The laboratory landslide test device of three part constituting by the model slotk and the catchment sink and rainfall system is developed according to test requirements, and it carried out to research calibration test of rainfall and correction of rainfall for rainfall systems under laboratory conditions. The calibration results of rainfall shown that the indoor rainfall increases linearly with time if the opening of the water-tap is reasonably controlled and that can ensure stability of the supplying water of the laboratory landslide test. The correction results of rainfall shown that, according to the energy balance method and volume method, the indoor rainfall can be converted the actual rainfall by the energy reduced coefficient in the indoor rainfall conditions and the actual rainfall conditions of the slope, and that ensure requirements of rainfall of laboratory landslide tests corresponding to the actual rainfall.The energy reduced coefficient is determined by landing speed of indoor raindrop and end speed of actual raindrop.