Average Rain Rate Research Articles

Model sensitivity in predicting extreme precipitation events in urban areas: A case study over Beijing

Understanding and forecasting the spatial and temporal distributions of extreme precipitation over urban areas is crucial for effective planning and mitigation efforts. However, this task remains challenging as accurate forecasting depends on properly representing urban surfacees and their interactions with the planetary boundary layer (PBL). We examined the hindcast of an extreme precipitation event over Beijing on 21–22 July 2012. The primary focus was assessing its sensitivity to two widely used PBL parameterizations (MYJ and YSU), two urban parameterizations (SLUCM and BEP_BEM), and two different land-use and land-cover (LULC) datasets.Sensitivity experiments were initialized at different times to explore the model dependence on initial conditions. The analyses were conducted over three selected regions: the entire model domain covering the Beijing metropolitan area, an upwind region of Beijing, and the entire urban area of Beijing. The results show that the MYJ PBL scheme performs better than the YSU PBL scheme in capturing near-surface air temperature as well as the location and timing of the heaviest precipitation. The variability in simulated precipitation among the chosen PBL schemes is lower compared to that among different time of initializations. The LULC impacted the spatial distribution of precipitation but its effect on the amount of precipitation was minimal. Overall, using a combination of the MYJ PBL scheme, SLUCM urban parameterization, and locally-enhanced Beijing LULC, and initializing the model simulations at 0000 UTC July 20, 2012, demonstrated superior performance in capturing precipitation levels, despite some spatial discrepancies in the precipitation distribution. The performance of BEP_BEM urban parameterization is similar to SLUCM across various factors such as average rain rate, maximum rain rate, and rain volume. These findings offer valuable insights towards better simulations of extreme precipitation and flooding in rapidly urbanizing areas such as Beijing.

Spatial Variability of Raindrop Size Distribution at Beijing City Scale and Its Implications for Polarimetric Radar QPE

Understanding the characteristics of the raindrop size distribution (DSD) is crucial to improve our knowledge of the microphysical processes of precipitation and to improve the accuracy of radar quantitative precipitation estimation (QPE). In this study, the spatial variability of DSD in different regions of Beijing and its influence on radar QPE are analyzed using 11 disdrometers. The DSD data are categorized into three regions: Urban, suburban, and mountainous according to their locations. The DSD exhibits evidently different characteristics in the urban, suburban, and mountain regions of Beijing. The average raindrop diameter is smaller in the urban region compared to the suburban region. The average rain rate and raindrop number concentration are lower in the mountainous region compared to both urban and suburban regions. The difference in DSD between urban and suburban regions is due to the difference in DSD for the same precipitation types, while the difference in DSD between mountain and plains (i.e., urban and suburban regions) is the combined effect of the convection/stratiform ratio and the difference of DSD for the same precipitation types. Three DSD-based polarimetric radar QPE estimators were retrieved and estimated. Among these three QPE estimators, R(ZH), R(Kdp), and R(Kdp, ZDR), R(Kdp, ZDR) performs best, followed by R(Kdp), and R(ZH) performs worst. R(Kdp) is more sensitive to the representative parameters, while R(ZH) and R(Kdp, ZDR) are more sensitive to observational error and systematic bias (i.e., calibration).

Analyzing Relationships between Tropical Cyclone Intensity and Rain Rate over the Ocean Using Numerical Simulations

Abstract In this study, the relationship between tropical cyclone (TC) intensity and rain rate over the ocean is investigated using a full-physics numerical model (WRF) and a physics-based TC rainfall model (TCR). TC intensity is found to be nearly linearly correlated with the average rain rate in the inner core [∼0.97 (mm h−1 m−2)/(m s−1)], while the correlation is weak at outer radii. This difference is induced because TC intensity is significantly correlated with both the vertical velocity and specific humidity in the inner core but is not significantly correlated with the vertical velocity in the outer radii. Further investigation shows that the intensity–rain-rate relationship at the outer radii is influenced by the TC evolution stage. The rain rate for the outer radii is positively correlated with TC intensity for nondecaying TCs, while this correlation is reduced for decaying TCs due to systematic downdrafts in the outer radii. In the context of climate change, the sensitivity of the TC rain rate to sea surface temperature (SST) is found to be +9% per 1 K increase of SST, roughly the product of the sensitivity of TC intensity to SST (+3%) and the Clausius-Clapeyron scaling (+7%). Coupled with synthetic storms, evolution of the TC rain rate over the twenty-first century under the SSP5-8.5 scenario is projected by the TCR (calibrated with the WRF simulations). The annual increase rates of averaged TC rain rate are 0.17% and 0.20% for the inner core and outer radii, respectively, larger than the annual increase rate of TC intensity (0.046%) but comparable to that of cube of intensity (0.18%).

Can DSD Assumptions Explain the Differences in Satellite Estimates of Warm Rain?

Abstract Satellite-based oceanic precipitation estimates, particularly those derived from the Global Precipitation Measurement (GPM) satellite and CloudSat, suffer from significant disagreement over regions of the globe where warm rain processes are dominant. GPM estimates of average rain rate tend to be lower than CloudSat estimates, due in part to GPM being less sensitive to shallow and/or light precipitation. Using coincident observations between GPM and CloudSat, we find that the GPM_2BCMB product misses about two-thirds of total accumulated warm rain compared to the CloudSat 2C-RAIN-PROFILE product. This difference becomes much smaller when products are compared at 1000 m above the surface (mitigating surface clutter issues) and when forcing the frequency of rain from CloudSat to match the frequency from GPM (mitigating sensitivity issues). However, even then a gap of about 25% remains. Using an optimal estimation retrieval algorithm on the underlying data, we retrieve a similar result, but find that the remaining difference between the GPM and CloudSat retrieved rain rates can be almost entirely accounted for by inconsistent assumptions about the shape of the drop size distribution (DSD) that are made in the two retrievals. We conclude that DSD assumptions contribute significantly to the relative underestimation of warm rain by GPM compared to CloudSat. Because the choice of DSD model has such a large effect on retrieved rain rates, more work is needed to determine whether the DSD models assumed by either the GPM_2BCMB or 2C-RAIN-PROFILE algorithms are actually appropriate for warm rain.

Analysis of the inner rainbands of tropical cyclones over the South China Sea during the landfall process

Tropical cyclones (TCs) can undergo offshore rapid intensification (RI) shortly before making landfall over the South China Sea (SCS). In this study, the inner rainbands distribution of both RI and non-RI landfall TCs (LTCs) in the SCS during 2015–2020 is examined based on a multi-source merged precipitation dataset. It is found that those RI LTCs exhibit a relatively higher averaged rain rate in the inner core region than that of non-RI LTCs. Both offshore RI cases and non-RI LTCs appear to have an increasing tendency of averaged rain rate after landfall, with the rain rate peak of the RI cases a few hours earlier than that of non-RI cases. By defining an axisymmetric index, the inner rainband evolution of both offshore RI cases and non-RI ones are further discussed. For both categories, most of the axisymmetric rainfall is concentric around the center and over 70% axisymmetric rainfall dominates the inner core region within three times of radius of maximum wind speed (RMW). It is shown that there is an obvious inwards shrinkage of axisymmetric rainfall for both offshore RI and non-RI cases. Analysis of typical RI and non-RI LTCs (1713 Hato and 1714 Pakhar) also shows an increasing rain rate of the inner rainbands soon after landfall, with larger amplitude for RI example than non-RI case. The inner rainbands of 1713 Hato show that a clockwise propagation with maximum enhancement happened at the down-shear left-hand side a few hours after landfall.

Vertical variation of tropical cyclone size in the western North Pacific

AbstractBased on the ERA5 reanalysis dataset, this paper examines the vertical variation of tropical cyclone (TC) size in the western North Pacific during 1998–2018. The TC size is defined as the distance from the TC centre to the radius at which the azimuthally averaged relative vorticity decreases to 1 × 10−5 s−1 (Rvor). It is found that TCs with similar sizes at the surface can be significantly different in size at higher levels. The Rvor at 10 m height (Rvor10) and that at 200 hPa (Rvor200) are related to TC intensity categories, and Rvor10 and that at 700 hPa (Rvor700) correlate linearly with the relative sea surface temperature (RSST) averaged within a 500‐km radius. Further, a positive correlation is found between the 500‐km radius averaged rain rate and Rvor200, while Rvor10, Rvor700 and Rvor200 all decrease with an increasing vertical wind shear (VWS). The spatial distributions of Rvor10, Rvor700, Rvor200 and Vmax, RSST, and rain rate are all similar to one another, and the spatial correlation coefficient between any pair of variations is larger than 0.91, which is statistically significant at the 0.01 level. The monthly variations of Rvor10, Rvor700 and Rvor200 are generally larger in the months with strong TC activity (May–October) than in the other months, although a peak of Rvor10 during March has been identified for the more recent few TCs. No significant interannual trend is found during 1998–2018 for any of the three variables (Rvor10, Rvor700 and Rvor200). Statistically significant correlations between the ENSO (El Niño–Southern Oscillation) index and Rvor10 and Rvor200 are 0.54 and 0.47, respectively, while no statistically significant correlation is found between the ENSO index and Rvor700. The mechanisms that affect the TC size at different heights are complicated and will be explored in later studies.

The peak runoff model based on Existing Land Use and Masterplan in Sentul City area, Bogor

This research aimed to create a peak runoff mode based on existing land use (LU) and masterplan in Sentul City area. To determine the peak runoff by rational method, the study uses the formulation as follows: Q = 0.2778.C.I.A, in which Q is the peak runoff, C is the runoff coefficient of area, I is the average rain rate intensity, and A is the area of study. For recognizing the existing LU, the researcher used image analysis SPOT-6 (2017) by supervised classification. It estimated the gamma distribution parameter through the maximum likelihood method by using software QGIS 2.8, SAGA GIS, dan Arc-GIS 10.4.1. According to the analysis, the study result showed the existing LU peak runoff coefficient value and masterplan are 0.40 and 0.61, respectively, in which the difference is 0.21. The peak runoff increase is 25.32 m3/sec or 6,622,560 m3/year as the impact of land-use change.

The Influence of Synoptic-Scale Air Mass Conditions on Seasonal Precipitation Patterns over North Carolina

This paper characterizes the influence of synoptic-scale air mass conditions on the spatial and temporal patterns of precipitation in North Carolina over a 16-year period (2003–2018). National Center for Environmental Prediction Stage IV multi-sensor precipitation estimates were used to describe seasonal variations in precipitation in the context of prevailing air mass conditions classified using the spatial synoptic classification system. Spatial analyses identified significant clustering of high daily precipitation amounts distributed along the east side of the Appalachian Mountains and along the Coastal Plains. Significant and heterogeneous clustering was prevalent in summer months and tended to coincide with land cover boundaries and complex terrain. The summer months were dominated by maritime tropical air mass conditions, whereas dry moderate air mass conditions prevailed in the winter, spring, and fall. Between the three geographic regions of North Carolina, the highest precipitation amounts were received in western North Carolina during the winter and spring, and in eastern North Carolina in the summer and fall. Central North Carolina received the least amount of precipitation; however, there was substantial variability between regions due to prevailing air mass conditions. There was an observed shift toward warmer and more humid air mass conditions in the winter, spring, and fall months throughout the study period (2003–2018), indicating a shift toward air mass conditions conducive to higher daily average rain rates in North Carolina.

Rain Rate Retrieval Test From 25-GHz, 28-GHz, and 38-GHz Millimeter-Wave Link Measurement in Beijing

Accurate rainfall monitoring is important, and previously it has been shown that microwave backhaul link between adjacent base station towers can be used for rainfall estimation. However, with the deployment of 5G using millimeter technology, there is opportunity for dense rainfall monitoring network using both backhaul and data transmission links. This paper presents our millimeter-wave measurement results during rainy days in Beijing, China. Our measurement design is an exemplary line-of-sight transmission link. We show that it is possible to retrieve the path-averaged rain rate from the measurement and to use both millimeter-wave transmission link and backhaul link to assist rainfall monitoring. Compared to the local rain measurement from rain gauge and disdrometer, we show that the correlation value of millimeter-wave link retrieved average rain rate varies between 0.6 and 0.9 for different rainfall events. There is room for improvement, and we find that if we can monitor the received signal for a sufficiently long period of time, we can quantify the bias due to fading and work out a better estimate of the rain retrieval model's reference level.

Aerosol-induced changes in the vertical structure of precipitation: a perspective of TRMM precipitation radar

Abstract. Our knowledge is still poor regarding the response of the precipitation vertical structure to aerosols, partly due to the ignorance of precipitation occurring at different spatial scales. A total of 6 years of collocated ground-based PM10 and satellite-based (Tropical Rainfall Measuring Mission, TRMM) radar data, along with ERA-Interim reanalysis, are used in this study to investigate the aerosol effects on three localized rain regimes (shallow, stratiform, and convective rain) over the Pearl River Delta region of China. A subjective analysis method is proposed to discriminate between the localized and synoptic-scale precipitations based on weather composite charts where daily averaged wind field at 850 hPa is overlaid with the geopotential height at 500 hPa. In general, average rain rate tends to be greater under polluted conditions than under clean conditions. But such potential aerosol effects are regime dependent: as the atmosphere becomes slightly polluted (PM10≤38 µg m−3), the top 1 % radar reflectivity (Z) for all regimes initially increases, followed by continued increases and weak decreases for convective and stratiform/shallow rain regimes, respectively. As the atmosphere becomes much more polluted, such regime dependences of aerosol effects are more significant. From a perspective of the vertical Z structure, comparisons between polluted conditions (days with the highest third of PM10 concentration) and clean conditions (days with the lowest third of PM10 concentration) show that the convective rain regime exhibits a deeper and stronger Z pattern, whereas a much shallower and weaker Z pattern is observed for stratiform and shallow precipitation regimes. In particular, the top height of the 30 dBZ rain echo increases by ∼29 % (∼1.27 km) for the convective regime, but decreases by ∼10.8 % (∼0.47 km) for the stratiform regime. However, no noticeable changes are observed for the shallow precipitation regime. Impacts of meteorological factors are further studied on both rain top height (RTH) and the center of gravity of Z, including vertical velocity, vertical wind shear, convection available potential energy, and vertically integrated moisture flux divergence (MFD). The possible invigoration effect on convective precipitation seems dependent on wind shear, in good agreement with previous findings. Overall, the observed dependence of the precipitation vertical structure on ground-based PM10 supports the notion of aerosol invigoration or suppression effect on cold or warm rain and adds new insights into the nature of the complex interactions between aerosol and various localized precipitation regimes.

On the Relationship between Intensity and Rainfall Distribution in Tropical Cyclones Making Landfall over China

AbstractTRMM satellite 3B42 rainfall estimates for 133 landfalling tropical cyclones (TCs) over China during 2001–15 are used to examine the relationship between TC intensity and rainfall distribution. The rain rate of each TC is decomposed into axisymmetric and asymmetric components. The results reveal that, on average, axisymmetric rainfall is closely related to TC intensity. Stronger TCs have higher averaged peak axisymmetric rain rates, more averaged total rain, larger averaged rain areas, higher averaged rain rates, higher averaged amplitudes of the axisymmetric rainfall, and lower amplitudes of wavenumbers 1–4 relative to the total rainfall. Among different TC intensity change categories, rapidly decaying TCs show the most rapid decrease in both the total rainfall and the axisymmetric rainfall relative to the total rain. However, the maximum total rain, maximum rain area, and maximum rain rate are not absolutely dependent on TC intensity, suggesting that stronger TCs do not have systematically higher maximum rain rates than weaker storms. Results also show that the translational speed of TCs has little effect on the asymmetric rainfall distribution in landfalling TCs. The maximum rainfall of both the weaker and stronger TCs is generally located downshear to downshear left. However, when environmental vertical wind shear (VWS) is less than 5 m s−1, the asymmetric rainfall maxima are more frequently located upshear and onshore, suggesting that in weak VWS environments the coastline could have a significant effect on the rainfall asymmetry in landfalling TCs.

A Ku-band wind and rain backscatter model at low-incidence angles using Tropical Rainfall Mapping Mission precipitation radar data

ABSTRACTThis article proposes a simple Ku-band wind and rain backscatter model at low-incidence angles for describing sea surfaces where rain is present. The data used consisted of the sea surface backscatter and averaged rain rates from Tropical Rainfall Mapping Mission precipitation radar (TRMM PR) measurements and the collocated 10 m height numerical prediction wind speeds from the European Centre for Medium-Range Weather Forecasts. From the rain effect analysis, it was found that the surface backscatter decreases with increases in the averaged rain rate. The rain-induced backscatter was clearly dependent of the wind speed and was slightly dependent of the incidence angle. On the basis of the analysis, the wind and rain backscatter model was simply defined as the sum of a wind backscatter model and a rain backscatter model. The wind backscatter model was provided with the given Ku-band low-incidence backscatter model. The rain-induced backscatter for specific incidence angles and wind speeds was modelled as a simple quadratic polynomial function of the averaged rain rate by using the collocated datasets. The wind and rain backscatter model was validated by other parts of the collocated datasets. Results showed that the new model-predicted total backscatter had a root mean square error of 1.02 dB and a correlation coefficient (r) of 0.73 with the collocated TRMM PR-measured rain-affected surface backscatter. Compared to the single wind backscatter model, the wind and rain backscatter model significantly improved the prediction accuracy for the surface backscatter in rain.

Method and experiment of path rainfall intensity inversion using a microwave link based on nonspherical rain-induced model

It is important to measure rainfall accurately with high spatial and temporal resolution in meteorology, hydrology, agriculture industry, environment conservation, flood warning and weather forecasting. The use of attenuated information about microwave propagation in rainfall areas to acquire surface precipitation intensity has been shown to be a practical approach to measuring rainfall in recent years. However, the inversion of a single-frequency link is based on the assumption of rainfall attenuation under a certain frequency condition. Further, obtaining parameters that comply with all rainfall events for the rainfall attenuation model is a challenge, often leading to an overestimation of the rainfall intensity. Therefore, based on extended boundary condition method and Gamma raindrop size distribution, an inversion method of the path rainfall intensity by using a microwave link rain-induced attenuation is proposed in order to improve the accuracy of rainfall measurement by microwave rain-induced attenuation. In this paper, we use the characteristics of an atmospheric attenuation model to eliminate the influence of non-rainfall-caused attenuation on the process of rainfall inversion. On the basis of scattering theory and by utilizing the Gamma raindrop size drop, we use the extended boundary condition method to calculate the characteristics of microwave attenuation for Pruppacher-Beard raindrop shape model. The correction model of rainfall effective attenuation and rainfall inversion model of line-of-sight microwave links are proposed, based on the microwave rain attenuation characteristics and raindrop size distribution statistics. In this paper, we propose 15-20 GHz inversion model of path-average rainfall intensity based on nonspherical rain-induced model by using Levenberg-Marquardt optimization algorithm. Meanwhile, we analyze the variations of parameters of rain-induced model under the condition of different temperatures. Besides, we design a line-of-sight microwave experimental system for measuring the rainfall, and the path average rain rate is inversed by rainfall inversion model, which is compared with an OTT disdrometer. The results show that the correlation coefficient of rain rate inversed by microwave link and that of disdrometer are both higher than 0.6 mostly, and the maximum value is 0.96; the error of accumulated rain amount is less than 2.47 mm, the minimum value is 0.28 mm; the relative error of accumulated rain amount is less than 1.84%, the minimum value is 0.44%. The experimental results validate the feasibility and accuracy of rainfall inversion method proposed in this paper. In addition, the experimental result reflects that rainfall intensity retrieved method based on nonspherical raindrop model has advantages over the method based on spherical raindrop model.

On the seasonal variation of various types of precipitation over global tropical ocean region: A perspective from TRMM measurements

The radar reflectivity and precipitation rate from Precipitation Radar (PR) onboard Tropical Rainfall Measuring Mission (TRMM) are obtained over the global tropical regions (35°S–35°N) during the period from 2007 to 2012, combined with coincident vertical velocity at 400 hPa ( ω 400 hPa), relative humidity at 850 hPa (RH850 hPa) and lower tropospheric stability (LTS) from European Centre for Medium-Range Weather Forecasts (ECMWF) reanalysis. First of all, the seasonal and spatial distribution of meteorological factors, including ω 400hPa, RH850 hPa, and LTS, together with rain rate are investigated. Next, four typical Regions of Interest (ROIs) and their individual seasons (i.e., favorable and non-favorable seasons for rainfall) are identified for further analysis by determining whether there exist most pronounced seasonal differences observed in ω 400 hPa. Meanwhile, rainy area, and rainfall of three precipitation types (i.e., shallow, stratus, and convection precipitation regimes) over the ROIs has been calculated. The three dimensional structures of individual precipitating system are analyzed, based on normalized contoured frequency by altitude diagram (NCFAD) and other statistical methods. Finally, with a focus on convection precipitation system, we give a quantitative description of the response of precipitation vertical structure to meteorological factors. Namely, how the rain echo top height (RTH), echo top height with reflectivity of 30 dBZ (ZTH30 dBZ), and reflectivity center of gravity (ZCOG) vary with ω 400 hPa, RH850 hPa, and LTS. In particular, (1) high rain rate dominates over intertropical convergence zone, which is characterized by strong updraft, sufficient moisture, and low LTS, showing the average rain rate is negatively associated with ω 400 hPa at both temporal and spatial scales. That is to say, lower ω 400hPa comes with more intensive rain rate. (2) The meteorological factors, along with average rain rate, exhibit appreciable seasonal variation. To be specific, negative (positive) ω 400 hPa anomalies is mostly found over the northern (southern) hemisphere in summer and autumn, as opposed to the patterns found in winter and spring. (3) In terms of the area with rainfall, the stratiform precipitating system accounts for more than 50% of the total area under investigation, followed by the convective precipitating system (about 30%), and the shallow precipitating system (less than 20%). In contrast, convective precipitating system, among others, takes the lead (about 65%) in contributing to the accumulated rainfall amount in the ROIs studied, followed by stratiform precipitating system (about 25%), and the shallow precipitating system (about 10%). (4) In the season with relatively higher ω 400 hPa, both rainy area and accumulated rainfall amount for all three types of precipitation show a increasing trend, irrespective of ROI. By comparison, rain rate and its vertical structures show large discrepancy, i.e., the intensity of convective precipitation system in favorable season tends to systematically increase as compared with that in non-favorable season. (5) The bulk precipitation system parameters used to describe convective precipitating system, including RTH, ZTH30 dBZ, and ZCOG, are observed to be elevated sharply with increasing ω 400 hPa and RH850 hPa. The same holds for the increasing LTS but with a smaller magnitude in the elevated height. This implies that ω 400 hPa and RH850 hPa most likely play a dominant role in dictating the vertical development of convection.

Assessing spatial precipitation uncertainties in a convective‐scale ensemble

New techniques have recently been developed to quantify the location‐dependent spatial agreement between ensemble members, and the spatial spread–skill relationship. In this article a summer of convection‐permitting ensemble forecasts are analysed to better understand the factors influencing location‐dependent spatial agreement of precipitation fields and the spatial spread–skill relationship over the UK. The aim is to further investigate the agreement scale method, and to highlight the information that could be extracted for a more long‐term routine model evaluation. Overall, for summer 2013, the UK 2.2 km grid spacing ensemble system was found to be reasonably well spread spatially, although there was a tendency for the ensemble to be overconfident in the location of precipitation. For the forecast lead times considered (up to 36 h), a diurnal cycle was seen in the spatial agreement and in the spatial spread–skill relationship: the forecast spread and error did not increase noticeably with forecast lead time. Both the spatial agreement and the spatial spread–skill were dependent on the fractional coverage and average intensity of precipitation. A poor spread–skill relationship was associated with a low fractional coverage of rain and low average rain rates. The times with a smaller fractional coverage, or lower intensity, of precipitation were found to have lower spatial agreement. The spatial agreement was found to be location dependant, with higher confidence in the location of precipitation to the northwest of the UK.

Spatial and Temporal Variability of Rainfall in the Alps–Mediterranean Euroregion

AbstractThis study describes the main patterns of rainfall distribution in the Alps–Mediterranean “Euroregion” using a ground radar and characterizes the associated processes using model output. The radar dataset spans 2009–12 with fine spatial (1 km) and temporal (5 min) resolutions. The most significant rain accumulations were observed in 2009 and 2010, and the most intense extreme events occurred in 2010. Conversely, 2012 was a dry year. Model output revealed that the wind shear, the pressure, and the meridional wind at low level were the three main factors explaining the rainfall variability between 2009 and 2012. At the monthly scale, the maximum of rain accumulation was observed in November along the coast. Results also showed that the most intense rain rates were observed during early summer and autumn in the “Pre-Alps.” The monthly variability was characterized by a displacement of extreme rain events from land to sea from late spring to winter. Correlation analyses showed that this displacement was essentially controlled by the convective available potential energy (CAPE). Rainfall showed a diurnal variability from April to August for the land areas of the Alps–Mediterranean Euroregion. The diurnal variability was significant during the spring and summer months, with maximal rain intensity between 1600 and 1800 UTC. The correlation of the rainfall with CAPE showed that this cycle was related to atmospheric instability. A secondary peak in average rain rate was observed during the early morning and was likely triggered by land breezes. The results highlighted that rainfall characteristics are extremely diverse in terms of intensity and distribution in this relatively small region.

Near-Surface Density Currents Observed in the Southeast Pacific Stratocumulus-Topped Marine Boundary Layer*

Abstract Density currents (i.e., cold pools or outflows) beneath marine stratocumulus clouds are characterized using 30 days of ship-based observations obtained during the 2008 Variability of American Monsoon Systems (VAMOS) Ocean–Cloud–Atmosphere–Land Study Regional Experiment (VOCALS-REx) in the southeast Pacific. An air density increase criterion applied to the Improved Meteorological (IMET) sensor data identified 71 density current front, core (peak density), and tail (dissipating) zones. The similarity in speeds of the mean density current propagation speed (1.8 m s−1) and the mean cloud-level advection relative to the surface layer wind (1.9 m s−1) allowed drizzle cells to deposit elongated density currents in their wakes. Scanning Doppler lidar captured prefrontal updrafts with a mean intensity of 0.91 m s−1 and an average vertical extent of 800 m. Updrafts were often surmounted by low-lying shelf clouds not connected to the overlying stratocumulus cloud. The observed density currents were 5–10 times thinner and weaker than typical continental thunderstorm cold pools. Nearly 90% of density currents were identified when C-band radar estimated areal average rain rates exceeded 1 mm day−1 over a 30-km diameter. Rather than peaking when rain rates were highest overnight, density current occurrence peaks between 0600 and 0800 local solar time when enhanced local drizzle co-occurred with shallow subcloud dry and stable layers. The dry layers may have contributed to density current formation by enhancing subcloud evaporation of drizzle. Density currents preferentially occurred in a large region of predominantly open cells but also occurred in regions of closed cells.

Evaluation of precipitation estimates over CONUS derived from satellite, radar, and rain gauge data sets at daily to annual scales (2002–2012)

Abstract. We use a suite of quantitative precipitation estimates (QPEs) derived from satellite, radar, and surface observations to derive precipitation characteristics over the contiguous United States (CONUS) for the period 2002–2012. This comparison effort includes satellite multi-sensor data sets (bias-adjusted TMPA 3B42, near-real-time 3B42RT), radar estimates (NCEP Stage IV), and rain gauge observations. Remotely sensed precipitation data sets are compared with surface observations from the Global Historical Climatology Network-Daily (GHCN-D) and from the PRISM (Parameter-elevation Regressions on Independent Slopes Model). The comparisons are performed at the annual, seasonal, and daily scales over the River Forecast Centers (RFCs) for CONUS. Annual average rain rates present a satisfying agreement with GHCN-D for all products over CONUS (±6%). However, differences at the RFC are more important in particular for near-real-time 3B42RT precipitation estimates (−33 to +49%). At annual and seasonal scales, the bias-adjusted 3B42 presented important improvement when compared to its near-real-time counterpart 3B42RT. However, large biases remained for 3B42 over the western USA for higher average accumulation (≥ 5 mm day−1) with respect to GHCN-D surface observations. At the daily scale, 3B42RT performed poorly in capturing extreme daily precipitation (> 4 in. day−1) over the Pacific Northwest. Furthermore, the conditional analysis and a contingency analysis conducted illustrated the challenge in retrieving extreme precipitation from remote sensing estimates.

Research on the method and experiment of path rainfall intensity inversion using a microwave link

Accurate measurement of rainfall with high spatial and temporal resolution have important significance in meteorology, hydrology, agriculture, environment, flood warning and weather forecasting, etc. Based on the rain-induced power-law attenuation, an inversion method of the path rainfall intensity is proposed by using a microwave link. Starting from the atmospheric gas absorption attenuation model, a correction model of rainfall effective attenuation and a rainfall inversion model for line-of-sight microwave links are proposed, based on the microwave rain attenuation characteristics and raindrop size distribution statistics. A line-of-sight microwave link is designed and used to measure the rainfall, and the path average rain rate is inversed by means of rainfall inversion model, which is compared with a disdrometer. Results show that the correlation coefficient of rain rate inversed by microwave link with that of disdrometer is higher than 0.6 mostly, and the maximum value is 0.9647; the error of the accumulated rain amount is less than 0.5 mm, and the minimum value is 0.0827 mm; the relative error of the accumulated rain amount is less than 15%, the minimum value is 3.3415%. Experiments confirm the feasibility and accuracy of rainfall inversion obtained using a microwave link.

A diagnostic study of spectral multiscaling on spatio-temporal accumulations of rainfall fields based on radar measurements over Iowa

Spectral multiscaling postulates a power-law type of scaling of spectral distribution functions of stationary processes of spatial averages or their temporal accumulations, over nested and geometrically similar sub-regions of the spatial parameter space of a given spatio-temporal random field. Presently, the validity of this property is investigated using time series of spatio-temporal accumulations of rain rate fields measured by a network of Doppler radars covering the region of Iowa. Statistical evidence of spectral multiscaling is gathered and discussed through a systematic study of appropriate regression diagnostics, using two records of data. One is a 120-month record of hourly (60-min) accumulations of spatially averaged rain rate on square pixels of side length 4km, comprising a rectangular grid of dimension 80×160 covering almost the entire State of Iowa. The other is a 74-month record of quarterly (15-min) accumulations of spatially averaged rain rate on square pixels of side length 1km, comprising a rectangular grid of dimension 68×106 over the Cedar River basin in eastern Iowa. The diagnostic results indicate frequency-dependent scaling relationships interpreted as evidence of spectral multiscaling across a range of spatial scales.