Stratiform Rainfall Research Articles

High‐Elevation Monsoon Precipitation Processes in the Central Andes of Peru

AbstractMeasurements at the high‐elevation Lamar Observatory in the Mantaro Valley (MV) in the Central Andes of Peru demonstrate a diurnal cycle of precipitation characterized by convective rainfall during the afternoon and nighttime stratiform rainfall with embedded convection. Wet season data (2016–2018) reveal long‐duration (6–12 hr) shallow precipitating systems (LDPS) that produced about 17% of monsoon rainfall in 2016 and 2018 associated with El Niño and La Niña, respectively. The LPDS fraction of monsoon rainfall doubles to 35% with weekly recurrence in 2017 under El Niño Costero (coastal) conditions. LDPS occur under favorable moisture conditions dictated by the South America (SA) Low‐Level Jet (SALLJ) and Cold Air Intrusions (CAIs). Backward trajectory analysis shows that precipitable water sustains >80% of seasonal precipitation and ties the LPDS to particular moisture source regions in the eastern Andes foothills 1–2 days in advance, enhanced by increased moisture supply in the midtroposphere. Higher frequency of CAIs and enhanced midlevel moisture convergence along CAI fronts explain the increased LDPS frequency during the 2017 El Niño Costero. These findings highlight the functional role of the Andes morphology in organizing moisture supply to high‐elevation precipitation systems on the orographic envelope. Analysis of the Global Precipitation Measurement (GPM) mission satellite‐based radar observations points to challenges to precipitation detection and estimation in this region as the GPM clutter‐free height (~1–2 km AGL) exceeds the depth of shallow precipitation systems in the MV.

Geographical Characteristics of Raindrop Size Distribution in the Southern Parts of South Korea

ABSTRACTThis study analyzed the regional characteristics of raindrop size distribution (DSD) in the southern coastal area of South Korea. Data from March 2016 to February 2017 were recorded by four Particle Size Velocity (PARSIVEL) disdrometers installed at intervals of ~20 km from the coastline to inland areas. Within 20 km from the coastline, multiple local maxima in the probability density function (PDF) were observed at mass-weighted mean diameter Dm = 0.6 mm and normalized intercept parameter logNw = 5.2 for stratiform rainfall, but these features were not observed more than 20 km from the coastline. On the basis of mean Dm–logNw values, stratiform rainfall clearly differed between coastal and inland areas. For convective rainfall, there was a linear relationship between Dm and Nw with distance from the coastline. PDF analyses of diurnal variation in DSD confirmed that in spring and autumn multiple local maxima appear in the daytime. The multiple local maxima in Dm and logNw were respectively lower and higher at nighttime than in the daytime in the spring and summer season. These features were highly dependent on the prevailing wind. There was a pattern of increasing A and decreasing b in the radar reflectivity–rainfall rate (Z–R) relationship (Z = ARb) with distance from the coastline, and these features were more pronounced in convective rainfall. These diurnal variabilities were regular in stratiform rainfall, and there were large differences in quantitative precipitation estimation depending on the land or sea breeze in the coastal area.

Calibration of the reflectivity-rainfall rate (Z-R) relationship using long-term radar reflectivity factor over the entire South Korea region in a Bayesian perspective

A fixed Z-R relationship approach, such as the Marshall-Palmer relationship, for an entire year and for different seasons can be problematic in cases where the relationship varies spatially and temporally throughout a region. From this perspective, this study explores the use of a long-term radar reflectivity factor for South Korea to obtain a nationwide calibrated power law relationship, Z=α∙Rβ, where R is the rainfall intensity and Z is the reflectivity factor, in the context of bias-correction and the associated uncertainties within a Bayesian regression framework. This study also investigates seasonal differences in the bias-correction parameters (i.e., additive and multiplicative bias-correction factors) and their roles in reducing systematic error. Distinct differences in the calibrated parameters over stations are identified, and more importantly, an inverse relationship between the two reflectivity parameters α and β (i.e., decreasing trend in β with increasing α) is clearly identified with different parameter space based on the seasons. A spatially structured pattern in the parameters exists, particularly parameter α, for the wet season and parameter β for the dry season. A pronounced region of high values in the power law parameters (i.e., α and β) during the wet and dry seasons may be partially due to the overestimation of the radar reflectivity factor associated with enhancement of moisture transport directly over the coastal region. Finally, the radar rainfall estimates through the calibrated Z-R relationship are compared with the currently used Z-R relationships for estimating stratiform rainfall and convective rainfall. Overall, the radar rainfall fields based on the proposed modeling procedure are similar to the observed rainfall fields, whereas the radar rainfall fields obtained from the currently used Marshall-Palmer Z-R relationship show a systematic underestimation. The calibrated Z-R relationships are further validated by testing the predictions of unseen radar-gauge pairs in the year 2018, in the context of cross-validation. The cross-validation results are largely similar to those in the calibration process, suggesting that the derived Z-R relationships fit the radar-gauge pairs reasonably well.

Convective Coupling in Tropical-Depression-Type Waves. Part I: Rainfall Characteristics and Moisture Structure

AbstractTropical-depression (TD)-type waves are synoptic-scale disturbances embedded with deep convection over the western North Pacific. Studies of these disturbances began over six decades ago; however, some properties of these disturbances remain vague, e.g., the coupling mechanism between the deep convection and the waves. This two-part study aims to examine the rainfall progression in TD-type disturbances and associated tropospheric moisture controlling convective rainfall. Part I investigates the rainfall and moisture characteristics of TD-type waves using TRMM-derived rainfall products and the ERA-Interim data during the period of June–October 1998–2013. The rainfall features a north–south asymmetrical pattern with respect to a TD-type disturbance, with enhanced convective and stratiform rainfall occurring in the southern portion. Along with the northwestward propagation, deep convective and stratiform rainfall occur in phase with the TD-type disturbance without significant preceding shallow convective rainfall. Following the deepest convection, shallow convective rainfall increases in the anomalous southerlies. Such a rainfall progression differs from the paradigm from shallow to deep convection, then to stratiform rainfall, which is suggested in other convectively coupled equatorial waves. The rainfall progression and the atmospheric moisture anomaly are phase locked to the TD-type disturbances such that the relative displacements change little when the disturbances propagate northwestward. The latent heat release in deep convection, which is obtained from the TRMM 3G25 dataset, superposes with a broad warm anomaly in the mid- to upper troposphere, suggesting wave growth through the generation of available potential energy from diabatic heating.

Seasonality in power law scaling of convective and stratiform rainfall with lightning intensity over Indian Monsoon regions

The power law relationship between the rain (RT) and lightning flash (LF) is useful for estimating rainfall over poorly gauged catchment areas of rivers over north-east India (NEI) and that between LF and storm top height (STH) is key to lightning parametrization in models. However, they are poorly constrained over the Indian monsoon region where potential for significant changes exists with large spatial variability of rainfall, strong land-ocean contrast, seasonality and contribution of stratiform to total rainfall. Using 16 years of TRMM-PR data and LIS data, here we examine the RT and LF relationship and between LF and STH during pre-monsoon and monsoon seasons over four regions, NEI, Central India (CI), Bay of Bengal (BoB) and Indian Ocean (IO). A stronger power law (exponent b = 0.71) during pre-monsoon than that during the monsoon season (b = 0.58) apply for convective rain over land (including BoB) while a weaker relationship is applicable for stratiform rain with b = 0.60, and b = 0.47 respectively. Over IO, the relationship is nearly identical for convective and stratiform rain with no seasonality (b ~ 0.4). A power law poorly represents the LF-STH relationship over land and fails over IO. A fifth power law is applicable only for pre-monsoon convective rain over land weakening to half in monsoon seasons (b = 2.48). For stratiform rain it is weaker with (b = 3.27) and (b = 1.67) for pre-monsoon and monsoon seasons respectively. Our findings suggest that one threshold based lightning parameterizations are inadequate and need to be generalized to include regional and seasonal differences unraveled here.

A comparison study of raindrop size distribution among five sites at the urban scale during the East Asian rainy season

To study difference at the urban scale (a few tens of kilometers), the raindrop size distribution (DSD) characteristics at five sites (Luhe (LH), Pukou (PK), Jingning (JN), Lishui (LS) and Gaochun (GC)) within five districts of Nanjing are compared using five years of PARticle SIze VELocity (PARSIVEL) disdrometer data during the East Asian rainy season. The percentage of class C5 (extreme rainfall) to rain amount at LH (industrial zone) is significantly higher than that at the other sites (up to 38%). In addition, LH has the largest log10Nw value, while JN (closest to the city center) has the largest Dm value for all rain rate classes and rainfall types. Compared with those of stratiform rainfall, the A and b values of convective rainfall from the Z-R relationship are remarkably more dispersed among the different sites. Moreover, the X-band is more robust to site differences than the S-band and C-band, and thus may be more suitable for rainfall monitoring at the urban scale.

Towards the connection between snow microphysics and melting layer: insights from multifrequency and dual-polarization radar observations during BAECC

Abstract. In stratiform rainfall, the melting layer (ML) is often visible in radar observations as an enhanced reflectivity band, the so-called bright band. Despite the ongoing debate on the exact microphysical processes taking place in the ML and on how they translate into radar measurements, both model simulations and observations indicate that the radar-measured ML properties are influenced by snow microphysical processes that take place above it. There is still, however, a lack of comprehensive observations to link the two. To advance our knowledge of precipitation formation in ice clouds and provide new insights into radar signatures of snow growth processes, we have investigated this link. This study is divided into two parts. Firstly, surface-based snowfall measurements are used to develop a new method for identifying rimed and unrimed snow from X- and Ka-band Doppler radar observations. Secondly, this classification is used in combination with multifrequency and dual-polarization radar observations collected during the Biogenic Aerosols – Effects on Clouds and Climate (BAECC) experiment in 2014 to investigate the impact of precipitation intensity, aggregation, riming and dendritic growth on the ML properties. The results show that the radar-observed ML properties are highly related to the precipitation intensity. The previously reported bright band “sagging” is mainly connected to the increase in precipitation intensity. Ice particle riming plays a secondary role. In moderate to heavy rainfall, riming may cause additional bright band sagging, while in light precipitation the sagging is associated with unrimed snow. The correlation between ML properties and dual-polarization radar signatures in the snow region above appears to be arising through the connection of the radar signatures and ML properties to the precipitation intensity. In addition to advancing our knowledge of the link between ML properties and snow processes, the presented analysis demonstrates how multifrequency Doppler radar observations can be used to get a more detailed view of cloud processes and establish a link to precipitation formation.

A Multiresolution Technique for the Classification of Precipitation Echoes in Radar Data

A new method for separating convective, intermediate, and stratiform rainfall based on the wavelet scale analysis is presented. A robust classification has resulted from the two choices: 1) the transformation of radar reflectivities to rain rates and 2) the inclusion of the intermediate class. The method uses a trous wavelet transform (WT) to separate heterogeneous convective features from the relatively smooth stratiform field. The heterogeneous region is further split into a convective class for the large wavelet coefficients and an intermediate class for the small wavelet coefficients. There is an improvement in the estimation of convective-stratiform fraction and frequency distribution of rain rates in comparison to the well-established Steiner method. The new method correctly reclassified a significant fraction of Steiner’s convective regions, which had low mean rain rates of 5.5 $\mathrm {mm}\cdot \mathrm {h}^{-1}$ , as stratiform regions. Similarly, Steiner’s stratiform regions, which had high mean rain rates of $15\,\,\mathrm {mm}\cdot \mathrm {h}^{-1}$ , are classified as convective by the wavelet method. The method is tested and evaluated over the Indian region during monsoon, and it is found that the three wavelet classes have distinct raindrop-size distributions.

Investigating the Role of Extreme Synoptic Patterns and Complex Topography During Two Heavy Rainfall Events in Crete in February 2019

During February 2019, two severe storms affected the island of Crete, located in south Greece. Both storms produced excessive rainfall, provoking severe damages, especially in the western part of Crete. The role of the prevailing synoptic patterns and the interaction of the flow with the high mountains of Crete were investigated. For this purpose, a variety of observational and numerical model data were exploited, including data from a dense rain gauge network, satellite imagery, and model analysis of various parameters describing the stability of the impinging flow. The first storm was a long-lasting event, with convective outbreaks embedded in a more stratiform rainfall pattern. The second storm was brief but mostly convection dominated. The analysis of the available data underlined the role of the low-level convergence upstream of the mountains during both storms, highlighting similarities and differences, as well as the role of the stability of the impinging flow. High soil moisture content was also evidenced as a key ingredient for the severe flooding that occurred during the second storm. This work complements similar studies on the role of Mediterranean islands and their topography on the spatial and temporal distribution of extreme rainfall.

Attenuation Correction of X-Band Radar Reflectivity Using Adjacent Multiple Microwave Links

Rain attenuation can hinder the implementation of quantitative precipitation estimations using X-band weather radar. Numerous studies have been conducted on correcting the attenuation of radar reflectivity by utilizing a dual-polarimetric radar and an arbitrary-oriented microwave link; however, there is a need to optimize the required number of microwave links and their locations. In this study, we tested four attenuation correction methods and proposed a novel algorithm based on the sole use of adjacent multiple microwave links. The attenuation of the X-band radar reflectivity was corrected by performing forward iterations at each link, and the correction coefficients were statistically analyzed to reduce the instability problem. The algorithms of each method were evaluated by studying the cases of convective and stratiform rainfall, and then validated by comparing the corrected reflectivity of the X-band radar with the qualitatively controlled reflectivity of the S-band radar. The new method was as efficient as the conventional method based on the specific differential phase of dual-polarimetric radar. Furthermore, the correction coefficient was more effectively optimized and stabilized using seven microwave links rather than a single link, and no further independent reference data were required. In addition, the attenuation correction also accounted for spatiotemporal differentiation depending on the rainfall type, and could recover the physical structure of the rainfall. The method developed herein can facilitate estimations of quantitative rainfall in developing countries where dual-polarization weather radars are not common. The exploitation of microwave link data is a promising method for rainfall remote sensing.

Two Layers of Melting Ice Particles Within a Single Radar Bright Band: Interpretation and Implications

AbstractDual‐frequency dual‐polarization radar observations of the melting of two ice populations in a stratiform rainfall event are presented. The observed phenomenon occurs as a two‐layer linear depolarization ratio (LDR) signature in a single radar bright band. Doppler spectra observations show that the upper LDR layer is caused by the melting of ice needles, potentially generated by the rime‐splintering process, while the lower one is mainly due to the melting of background ice particles formed at the cloud top. The melting signal of small needles acts as a unique benchmark for detecting the onset of melting and is used to verify the current methods for the identification of melting layer boundaries. The radar‐derived characteristics of the melting layer are found to be dependent on the radar variable and frequency used. The implications of the presented findings for radar‐based studies of precipitation properties in and above the melting layer are also discussed.

Diurnal Cycle of Precipitation Over the Maritime Continent Under Modulation of MJO: Perspectives From Cloud‐Permitting Scale Simulations

AbstractCloud‐permitting scale (3 km) simulations are made to investigate the diurnal cycle of precipitation (DCP) over the Indo‐Pacific Maritime Continent under the modulation of the Madden‐Julian Oscillation (MJO), focusing on January–February 2018 during the Years of the Maritime Continent (YMC). Comparisons with satellite precipitation and global reanalysis products show that the simulations reasonably capture main features of diurnal wind and precipitation. The MJO modulates the amplitude, timing, and propagation of the DCP through affecting both large‐scale and local circulation and convection. Under local suppressed conditions, much strengthened sea/valley breezes are generally responsible for the enhanced and earlier‐triggered (2‐ to 3‐hr lead) DCP over land. Meanwhile, stronger cooling induced by enhanced stratiform rainfall excites well‐developed gravity waves spreading outward and upward, accompanied by continuous decreases in low‐level temperature and amplified land breezes, which cause stronger and further offshore‐propagating DCP. The opposite is true under local active conditions. Modulated by the passing of MJO, the enhanced DCP also displays a systematic shift from the west to the east coasts of large islands, forming a unique dipolar structure in the anomalous island DCP. The DCP exhibits island‐dependent characteristics: With topographical elevation, the triggering mechanism of island convection transforms from later penetrating sea breeze fronts over mountain foothills to early‐excited valley winds over mountain tops. Steep topography also supports stronger intraseasonal variations of the DCP, which can be well explained by regional variations in land‐sea/mountain‐valley breezes, terrain lifting, and ambient wind‐induced advective and vertical wind shear effects.

Reconstructing the 2015 Salgar flash flood using radar retrievals and a conceptual modeling framework in an ungauged basin

Abstract. On 18 May 2015, a severe rainfall event triggered a flash flood in the municipality of Salgar, located in the northwestern Colombian Andes. This work aims to reconstruct the main hydrological features of the flash flood to better understand the processes modulating the occurrence of the event. Radar quantitative precipitation estimates (QPEs), satellite information, and post-event field visits are used to reconstruct the Salgar flash flood, in an ungauged basin, addressing the relationship among rainfall spatiotemporal structure, soil moisture, and runoff generation during successive rainfall events by using a conceptual modeling framework including landslide and hydraulic submodels. The hydrological model includes virtual tracers to explore the role of runoff and subsurface flow and the relative importance of convective and stratiform precipitation in flash flood generation. Despite potential shortcomings due to the lack of data, the modeling results allow an assessment of the impact of the interactions between runoff, subsurface flow, and convective–stratiform rainfall on the short-term hydrological mechanisms leading to the flash flood event. The overall methodology reproduces the magnitude and timing of the La Liboriana flash flood peak discharge considerably well, as well as the areas of landslide occurrence and flood spots, with limitations due to the spatial resolution of the available digital elevation model. Simulation results indicate that the flash flood and regional landslide features were strongly influenced by the antecedent rainfall, which was associated with a northeasterly stratiform event. The latter recharged the gravitational and capillary storages within the model, moistening the entire basin before the occurrence of the flash flood event and impacting the subsurface–runoff partitioning during the flash flood event. Evidence suggests that the spatial structure of the rainfall is at least as important as the geomorphological features of the basin in regulating the occurrence of flash flood events.

Raindrop size distribution and microphysical characteristics of a great rainstorm in 2016 in Beijing, China

This paper analyzes the characteristics of rain drop size distributions (DSDs) and vertical profiles of hydrometeors for a severe rainstorm event that occurred in Beijing, northern China, from 19 to 21 July 2016 using in situ measurements from two disdrometers (OTT-Parsivel2 and 2D-Video-Distrometer) and remote sensing data collected by a second-generation Micro Rain Radar (MRR2). This rainstorm was characterized by stratiform precipitation with embedded strong convection on 19 July and widespread, intense mixed convective-stratified rainfall resulting in persistent rainfall between 20 and 21 July. The temporal and spatial variations in rainfall rate R, liquid water content W, reflectivity Z, DSDs and the gamma DSD parameters in different precipitation episodes of this event are derived and compared between two meteorological stations in Beijing. Rainfall throughout the entire event was characterized by large concentrations of small- to medium-sized raindrops (diameters between 2 and 4 mm) and few larger particles (D > 4 mm), resulting in small values of reflectivity Z (<40 dBZ) and liquid water content W (<1.0 g m−3). In addition, the log10Nw-Dm scatter pairs recorded during the convective phase of this rainstorm indicate maritime-like convection. The time evolution of DSDs shows that most single peak DSDs occurred during stratiform rainfall, and bimodal DSDs were observed when the convective rainfall cells passed by and collisional breakups occurred. The gamma DSD model with a single peak in the stratiform phase of the storm and the bimodal DSD in the convective episode of the storm are quantitatively evaluated. In addition, in each precipitation episode, the differences in exponent b and coefficient A of the Z-R relationship between the two stations are smaller for stratiform rainfall than for convective rainfall due to the more evident variability of drop size and number concentration in convective rain. The physical nature of this relationship and the possible mechanisms leading to diverse characteristics in different phases of this heavy rainstorm are discussed.

Convective‐Stratiform Rainfall of Typhoon Fitow (2013): Sensitivity to Rainfall Partitioning Methods

AbstractRainfall separation methods are widely used in literatures, with some algorithms applied to surface rainfall and some applied to radar or other observations. How the effectiveness or practicability of these rainfall partitioning algorithms when applied to model results is not well known. In this study, three convective‐stratiform rainfall partitioning methods are compared and evaluated by analyzing cloud properties and associated precipitation budgets based on both observations and grid‐scale simulations from a three‐dimensional Weather Research and Forecasting modeling of Typhoon Fitow (2013). Results show that convective‐stratiform rainfall separation based on surface rain rate is generally more reasonable than that based on radar reflectivity in terms of statistics of vertical velocity and raindrop microphysical budgets. The radar reflectivity partition method does not conduct an exact demarcation between convective and stratiform regions, since the rainfall in stratiform region has similar characteristics as convective rainfall, whereas the rainfall classified as convective rainfall has similar characteristics as stratiform rainfall. Observational analysis based on satellite and lightning confirms these results and shows that the rainfall separation based on surface rain rate generally detects the cellular convective rainfall near eyewall and isolated convection in spiral rainbands, whereas the rainfall separation based on radar reflectivity not only fails to identify the scattered convective rainfall but also overestimates the convective rainfall embedded among the stratiform regions. Above all, the method based on surface rainfall produces more reasonable statistical and microphysical characteristics for both convective and stratiform regions of precipitation, which generally agree with the real rainfall distributions from satellite and lightning observations.

Diurnal Cycle of Raindrops Size Distribution in a Valley of the Peruvian Central Andes

In the Central Andes of Peru, convective and stratiform rainfall occurs, frequently associated with convective storms. The raindrop size distributions (RSD), measured by a Parsivel-2 optical disdrometer, were characterized by the variation of their normalized parameters. The RSD dataset includes measurements corresponding to 18 months between 2017 and 2019. As a result, it was found that the mass-weighted mean diameter Dm and the Nw parameter present respectively high and low values, in the interval of 15–20 LST (local standard time), wherein deeper and more active clouds appear. The events including convective rainfall contribute 67.5% of the accumulated total, wherein 92% corresponds to the 15–20 LST interval. It is concluded that the spectral variability of the RSD is strongly controlled by the cloudiness configuration field developing over the west (convection over highlands) and east (convection over Amazon) sides of the valley. In the afternoon, clouds develop and drift to the east, over the Andean valleys and towards the Amazon, intensified by local orographic circulation. The opposite happens at night, when the stratiform rainfall is dominant and it is controlled by clouds, located in the Inter-Andean valley, generated by the convection fields formed over the Amazon forest.

The Latitudinal Variability of Oceanic Rainfall Properties and Its Implication for Satellite Retrievals: 1. Drop Size Distribution Properties

AbstractIn this study, we analyze an in situ shipboard global ocean drop size distribution (DSD) 8‐year database to understand the underpinning microphysical reasons for discrepancies between satellite oceanic rainfall products at high latitudes reported in the literature. The natural, latitudinal, and convective‐stratiform variability of the DSD is found to be large, with a substantially lower drop concentration with diameter smaller than 3 mm in the Southern hemisphere high latitude (S‐highlat, south of 45°S) and Northern Hemisphere polar latitude (N‐polar, north of 67.5°S) bands, which is where satellite rainfall products most disagree. In contrast, the latitudinal variability of the normalized oceanic DSD is small, implying that the functional form of the normalized DSD can be assumed constant and accurately parameterized using proposed fits. The S‐highlat and N‐polar latitude bands stand out as regions with oceanic rainfall properties different from other latitudes, highlighting fundamental differences in rainfall processes at different latitudes and associated specific challenges for satellite rainfall retrieval techniques. The most salient differences in DSD properties between these two regions and the other latitude bands are: (1) a systematically higher (lower) frequency of occurrence of rainfall rates below (above) 1 mm h‐1, (2) much lower drop concentrations, (3) very different values of the DSD shape parameter (μ0) from what is currently assumed in satellite radar rainfall algorithms, and (4) very different DSD properties in both the convective and stratiform rainfall regimes. Overall, this study provides insights into how DSD assumptions in satellite radar rainfall retrieval techniques could be refined.

Simulations of Microphysics and Precipitation in a Stratiform Cloud Case over Northern China: Comparison of Two Microphysics Schemes

Using the Weather Research and Forecasting (WRF) model with two different microphysics schemes, the Predicted Particle Properties (P3) and the Morrison double-moment parameterizations, we simulated a stratiform rainfall event on 20-21 April 2010. The simulation output was compared with precipitation and aircraft observations. The aircraft-observed moderate-rimed dendrites and plates indicated that riming contributed significantly to ice particle growth at the mature precipitation stage. Observations of dendrite aggregation and capped columns suggested that aggregation coexisted with deposition or riming and played an important role in producing many large particles. The domain-averaged values of the 24-h surface precipitation accumulation from the two schemes were quite close to each other. However, differences existed in the temporal and spatial evolutions of the precipitation distribution. An analysis of the surface precipitation temporal evolution indicated faster precipitation in Morrison, while P3 indicated slower rainfall by shifting the precipitation pattern eastward toward what was observed. The differences in precipitation values between the two schemes were related to the cloud water content distribution and fall speeds of rimed particles. P3 simulated the stratiform precipitation event better as it captured the gradual transition in the mass-weighted fall speeds and densities from unrimed to rimed particles.

Analysis of a Precipitation System that Exists above Freezing Level Using a Multi-Parameter Phased Array Weather Radar

An X-band multi-parameter phased array weather radar (MP-PAWR) was developed in 2017. The scan concept of the MP-PAWR is electronic scanning in elevation by combining fan beam transmissions and pencil beam receptions with digital beam-forming techniques and mechanical scanning along the azimuth. The MP-PAWR realized three-dimensional (60 km in radius and 15 km in height) observations without gaps of 30 s. Although the MP-PAWR is supposed to be suitable for observations of rapidly changing convective systems, it can be advantageous for observations of stratiform rainfall because of continuous vertical pointing observations and its ability to apply the Velocity Azimuth Display (VAD) method with a constant radius for a vertical profile of dynamic parameters such as divergence and deformation. In this study, a precipitation system that existed mainly above the freezing level (in this case, it was approximately 5 km in height) observed from 14:00 to 17:00 Japan Standard Time on 6 September 2018 was analyzed using MP-PAWR data. The averaged area of the vertical profile of Z, and the Doppler velocity with fixed elevation showed a stationary structure with time. The average differential reflectivity factor (ZDR) profile with fixed elevation angles showed values that were close to zero and increased with height. Similar characteristics were shown in the average Specific Differential Phase (KDP) profile. Vertical pointing data, especially for Z, ZDR, and Doppler velocity, were utilized when the echo passed over the radar site, and the Doppler velocity showed the acceleration of fall speed below the freezing level. The vertical profile of divergence with a fixed radius was calculated using the VAD method, and the vertical velocity was calculated using the fall speed profile from the vertical pointing data and by assuming the vertical velocity at the cloud base was zero. The results indicate that the updraft region corresponds to higher ZDR and KDP regions.

Effect of disdrometer type on rain drop size distribution characterisation: a new dataset for south-eastern Australia

Abstract. Knowledge of the full rainfall drop size distribution (DSD) is critical for characterising liquid water precipitation for applications such as rainfall retrievals using electromagnetic signals and atmospheric model parameterisation. Southern Hemisphere temperate latitudes have a lack of DSD observations and their integrated variables. Laser-based disdrometers rely on the attenuation of a beam by falling particles and are currently the most commonly used type of instrument to observe the DSD. However, there remain questions on the accuracy and variability in the DSDs measured by co-located instruments, whether identical models, different models or from different manufacturers. In this study, raw and processed DSD observations obtained from two of the most commonly deployed laser disdrometers, namely the Parsivel1 from OTT and the Laser Precipitation Monitor (LPM) from Thies Clima, are analysed and compared. Four co-located instruments of each type were deployed over 3 years from 2014 to 2017 in the proximity of Melbourne, a region prone to coastal rainfall in south-eastern Australia. This dataset includes a total of approximately 1.5 million recorded minutes, including over 40 000 min of quality rainfall data common to all instruments, equivalent to a cumulative amount of rainfall ranging from 1093 to 1244 mm (depending on the instrument records) for a total of 318 rainfall events. Most of the events lasted between 20 and 40 min for rainfall amounts of 0.12 to 26.0 mm. The co-located LPM sensors show very similar observations, while the co-located Parsivel1 systems show significantly different results. The LPM recorded 1 to 2 orders of magnitude more smaller droplets for drop diameters below 0.6 mm compared to the Parsivel1, with differences increasing at higher rainfall rates. The LPM integrated variables showed systematically lower values compared to the Parsivel1. Radar reflectivity–rainfall rate (ZH–R) relationships and resulting potential errors are also presented. Specific ZH–R relations for drizzle and convective rainfall are also derived based on DSD collected for each instrument type. Variability of the DSD as observed by co-located instruments of the same manufacturer had little impact on the estimated ZH–R relationships for stratiform rainfall, but differs when considering convective rainfall relations or ZH–R relations fitted to all available data. Conversely, disdrometer-derived ZH–R relations as compared to the Marshall–Palmer relation ZH=200R1.6 led to a bias in rainfall rates for reflectivities of 50 dBZ of up to 21.6 mm h−1. This study provides an open-source high-resolution dataset of co-located DSD to further explore sampling effects at the micro scale, along with rainfall microstructure.