Diurnal Variation Of Precipitation Research Articles

Northeastward propagation of nocturnal precipitation over the Sichuan Basin

AbstractThe Sichuan Basin (SCB) is located to the east of the Tibetan Plateau (TP) and features nocturnal precipitation. This study explores spatial variation of nocturnal precipitation during the warm season over the SCB using high spatiotemporal resolution merged precipitation products from 2008 to 2017. It is found that there is a prominent northeastward timing delay of precipitation peak over the SCB, that is, the diurnal peak of precipitation occurs in the midnight over the southwestern SCB whereas in the early morning over the northeastern SCB. This time delay is partly ascribed to a northeastward propagation of precipitation over the SCB, account for about 40% and 25% of the diurnal variation of precipitation over the central and northeastern SCB, respectively. Precipitation first occurs over the southwestern edge of the SCB at about 1900–2000 LST, and then propagates northeastward steered by the large‐scale mid‐tropospheric southwesterly airflow, which is consistent with the northeastward propagation of the large moisture convergence. The precipitation reaches the northeastern SCB in the early morning. The diurnal variation of 850‐hPa wind has strong easterly wind deviations in the early evening over the southwestern SCB, which favours for an initiation of precipitation by orographic lift of air. The diurnal variation of difference in equivalent potential temperature between 500 hPa and 850 hPa has a maximum negative deviation in the early evening over the southwestern SCB, which enhances the instability and therefore favours an initiation of precipitation. The Yunnan‐Guizhou Plateau (YGP) may play an important role in the initiation of precipitation over the southwestern SCB in the early evening.

Effects of Convection Representation and Model Resolution on Diurnal Precipitation Cycle Over the Indian Monsoon Region: Toward a Convection‐Permitting Regional Climate Simulation

AbstractThis study investigated the reproducibility of rainfall characteristics of the Indian summer monsoon using a regional climate model (RCM), focusing on the convection representation and model horizontal grid resolution. To understand the importance of convection representation and model horizontal grid resolution, the study employed the Weather Research and Forecasting model WRFv3.8.1 as the RCM. Two series of experiments, that is, cumulus parameterization on/off (CON/COFF), were performed for the monsoon with three different spatial resolutions. Three contrasting monsoon years were selected for the simulations. The simulated rainfalls were evaluated with the India Meteorological Department data set and Tropical Rainfall Measurement Mission 3B42 Version 7. The results revealed that COFF captured fundamental aspects of the rainfall characteristics, such as diurnal cycle, rainfall intensity, and rainfall frequency. Over central India, in COFF, the diurnal precipitation peaks were simulated in afternoon/evening in close agreement with the observations. However, the diurnal precipitation peak in CON appeared 3–6 hr earlier than the observations. The diurnal precipitation variation was more associated with the horizontal grid resolution of the numerical model than representation of convection. Additionally, COFF could simulate diurnally propagating rainfall systems over the Bay of Bengal. Over the Indian land area, COFF simulated less‐frequent intense precipitation systems, whereas CON simulated more‐frequent widespread weak precipitation. This study demonstrated that convection representation is very important for simulation of diurnal rainfall systems over the Indian monsoon region, although refinement of model horizontal grid resolution is required over mountainous regions, where precipitation is closely related to orography.

Ground‐Based Observations Reveal Unique Valley Precipitation Patterns in the Central Himalaya

AbstractWhile the Himalayas act as a natural barrier to water vapor transport to the Tibetan Plateau, many north‐south‐oriented valleys channel moisture onto the Plateau. However, owing to the lack of in situ data, the spatiotemporal characteristics of precipitation remain unclear along these valleys. In this study, a high‐altitude (2,800–4,500 m above mean sea level) rain‐gauge network was established in the Yadong Valley, one of the main valleys in the central Himalayan Region (CHR). New observations from this network are used to evaluate the Integrated Multi‐satellitE Retrieval for Global Precipitation Measurement (IMERG) precipitation product, with results demonstrating that the IMERG data can reproduce the seasonal and diurnal patterns of precipitation seen in the observational data. This combination of in situ and IMERG precipitation data reveals two unique characteristics in the CHR. First, precipitation during the premonsoon season (March‐May) contributes 20–40% of the annual total, from the high altitudes of the CHR to Southeast Tibetan Plateau, due to water vapor flux conveyed by southwesterlies from the Bay of Bengal, whereas this percentage is much lower in the northern Himalaya and South Asia. Second, diurnal variations in precipitation during the monsoon season (June‐September) vary between the low and high altitudes of the north‐south‐oriented valleys in the CHR: Precipitation at high altitudes has two peaks (one in the afternoon and the other at night), which is different from the single nighttime peak in low altitudes that is usually reported. These two notable spatiotemporal characteristics are indicative of the unique climate that exists at the high altitudes of the CHR.

Temporal and spatial variations of convection, clouds and precipitation over the Tibetan Plateau from recent satellite observations. Part II: Precipitation climatology derived from global precipitation measurement mission

AbstractThis sequence of papers examines spatio‐temporal variations of precipitation over the Tibetan Plateau (TP) based on satellite observations. Here in Part 2, spatial patterns of seasonal and diurnal variations of precipitation have been examined based on the Global Precipitation Measurement Mission (GPM) and three additional satellite products. The results show a spatial dipole pattern of two distinct seasonalities: The central TP is marked by strong July peaks and exhibits rainfall contributions of the monsoon season (May–September) of more than 70%, whereas northwestern and southern regions of the plateau exhibit significantly smaller amplitudes in the annual cycle. In some southern regions which are characterized by very high summer mean precipitation and more extreme rain rates, winter months (October–April) contribute significantly to the total annual mean precipitation. In addition, there are larger differences in seasonal curves along a west‐to‐east axis, than along a north‐to‐south axis. The spatial patterns of diurnal precipitation over the TP are more complex compared to seasonality and point to multiple components, which construct the regional differences. These show also a seasonal dependence and are characterized by a stronger afternoon to early evening peak (17:00 LST time, 11:00 UTC) and weaker nighttime peak (23:00 LST, 17:00 UTC) during the monsoon season and over the plateau compared to its surroundings. Furthermore, it was shown that convective precipitation during the monsoon season contribute only up to 30% to the total precipitation, whereas more than 70% is produced by the 90th percentile of daily rain rates. An important characteristic of summer precipitation is hence that a significant part of the extreme precipitation is non‐convective. This paper reveals new features of spatial patterns in seasonal and diurnal precipitation and highlights the importance of non‐monsoonal components for seasonal precipitation variations.

Diurnal Variation of Meiyu Rainfall in the Yangtze Plain During Atypical Meiyu Years

AbstractThe diurnal variation of precipitation reflects the influence of atmospheric heat and dynamic processes on the water cycle. Using multiple data sets, we carried out case studies and statistical analysis of the diurnal variation in Meiyu rainfall in atypical Meiyu years. Our results show that the morning precipitation was induced by strong southwesterly moisture transport and was mainly composed of stratiform pixels, whereas the precipitation occurring in the afternoon was mainly composed of convective pixels affected by updrafts. The diurnal variation in precipitation in the atypical Meiyu years appeared as a bimodal structure with peaks in early morning (06:30 LST) and afternoon (16:00 LST), which was different from the single morning peak (09:30 LST) in the normal Meiyu years and reported previously. Further research indicated that the morning peak is related to the low‐level water vapor flux, whereas the afternoon peak is related to the local solar heating. In addition, the water vapor flux in the Yangtze Plain was characterized by strong morning and weak afternoon fluxes during both normal and atypical Meiyu periods. The diurnal variation in the low‐level water vapor flux is thought to be influenced by the intensity of, and distance from, the subtropical high.

Intercomparison of CRA-Interim Precipitation Products with ERA5 and JRA-55

Based on the hourly observational data during 2007-2016 from surface meteorological stations in China, this paper compares the influence of 3-hourly precipitation data, mainly from the Chinese Reanalysis-Interim (CRA-Interim), ECMWF Reanalysis 5 (ERA5) and Japanese Reanalysis-55 (JRA-55), on the simulation of the spatial and temporal distribution of regional precipitation in China and the bias distribution of the simulation. The results show that: (1) The three sets of reanalysis datasets can all reflect the basic spatial distribution characteristics of annual average precipitation in China. The simulation of topographic forced precipitation in complex terrain by using CRA-interim is more detailed, while CRA-interim has larger negative bias in central and East China, and larger positive bias in southwest China. (2) In terms of seasonal precipitation, the three sets of reanalysis datasets overestimate the precipitation in the heavy rainfall zone in spring and summer, especially in southwest China. According to CRA-interim, location of the rain belt in the First Rainy Season in South China is west by south, and the summer precipitation has positive bias in southwest and South China. (3) All of the reanalysis datasets can basically reflect the distribution difference of inter-annual variation of drought and flood, but overall the CRA-Interim generally shows negative bias, while the ERA5 and JRA-55 exhibit positive bias. (4) For the diurnal variation of precipitation in summer, all the reanalysis datasets perform better in simulating the daytime precipitation than in the night, and the bias of CRA-interim is less in the Southeast and Northeast than elsewhere. (5) The ERA5 generally performs the best on the evaluation of quantitative precipitation forecast, the JRA-55 is the next, followed by the CRA-Interim. The CRA-Interim has higher missing rate and lower threat score for heavy rains; however, at the level of downpour, the CRA-Interim performs slightly better.

Spatiotemporal Variations of Precipitation in Bangladesh Revealed by Nationwide Rain Gauge Data

Bangladesh is under the strong influence of the South Asian monsoon. Extensive damages caused by frequent severe flood events in this country call for a study of nationwide precipitation climatology. Here, we examine spatiotemporal variations of precipitation in Bangladesh using rain gauge data at 35 stations for the period 2003–2016. The annual precipitation amount in Bangladesh is 2263 mm, and it shows large spatial variations. The annual precipitation amount is large in the southeastern coastal region of the country and the region close to the Meghalaya Plateau, and it is small in the west central region. 17% and 73% of the annual precipitation amount are observed in the pre-monsoon season (March to May) and monsoon season (June to September), respectively. The pattern of the diurnal variation of precipitation differs depending on regions of Bangladesh. In the northern region of the country, the precipitation maximum occurs in the late night to early morning in both the pre-monsoon and monsoon seasons. The late night to early morning maximum of precipitation is associated with the large horizontal convergence of low-level water vapor flux. The Himalaya Mountains and the Meghalaya Plateau together with more nighttime moisture transport due to the strengthened nighttime low-level wind seem to play roles in enhancing nighttime precipitation. In the southwestern region of the country, the precipitation maximum is observed in the early evening in the pre-monsoon season, which is associated with the large convective instability in the afternoon, and it is observed in the early afternoon in the monsoon season. In the southeastern region of the country, the diurnal variability of precipitation is smallest in the pre-monsoon season compared with other regions of the country in the pre-monsoon and monsoon seasons and the precipitation maximum occurs in the late night to early morning in the monsoon season.

Seasonal changes of the diurnal variation of precipitation in the upper Río Chagres basin, Panamá.

This study elucidated the characteristics of climatological seasonal changes in the diurnal variations of precipitation at four ground stations in the upper Río Chagres basin in the Panama Canal watershed. The seasonal changes differed among the stations, although they are located within an area of only 414 km2. Precipitation peaks in the early afternoon at 1500 local standard time (LST) were observed at all the stations. At Chamon, monthly-mean hourly precipitation at every hour exceeded 0.3 mm h–1 throughout November and December. The occurrence of morning precipitation in January and March distinguished the seasonal precipitation pattern at Esperanza from the pattern at the other stations. Analyses of the seasonal changes in the diurnal variation with pattern correlations and rotational empirical orthogonal functions grouped the stations into two pairs: no morning peak at Chico and Río Piedras in the downstream basin and morning peak at Chamon and Esperanza in the upstream basin.

Land–Sea Contrast in the Diurnal Variation of Precipitation from Landfalling Tropical Cyclones

AbstractRecent composite analysis of landfalling tropical cyclones (TCs) suggests a rain rate peak in the early morning, which contradicts the typically observed peak in convective precipitation over land seen in the late afternoon to early evening. We conducted a set of idealized simulations of TCs and analyzed observational data from TC Bebinca (2018), which stalled near the shoreline of southern China. We show a distinct land–sea contrast in the diurnal variation of TC precipitation and an 8–12 hr offset between the peak precipitation time over land compared with that over the sea in a TC that stalls at the shoreline. The highest land surface temperature and maximum low‐level buoyancy during the afternoon led to peak precipitation over land at this time. However, the peak precipitation over the sea in the early morning was generated by the increase in relative humidity caused by nighttime radiative cooling and enhanced instability.

Influences of Lake Malawi on the spatial and diurnal variability of local precipitation

Abstract. We investigate how the intensity and spatial distribution of precipitation vary around Lake Malawi on a diurnal timescale, which can be valuable information for water resource management in tropical south-eastern African nations. Using a state-of-the-art satellite product and regional atmospheric model, the well-defined diurnal cycle is detected around Lake Malawi with harmonic and principle component analyses: the precipitation is intense during midnight to morning over Lake Malawi and the precipitation peaks in the daytime over the surrounding area. This diurnal cycle in the precipitation around the lake is associated with the lake–land breeze circulation. Comparisons between the benchmark simulation and an idealized simulation in which Lake Malawi is removed reveal that the diurnal variations in precipitation are substantially amplified by the presence of Lake Malawi. This is most evident over the lake and surrounding coastal regions. Lake Malawi also enhances the lake–land breeze circulation; the nocturnal lakeward land breeze generates surface convergence effectively and precipitation intensifies over the lake. Conversely, the daytime landward lake breeze generates the intense divergence over the lake and precipitation is strongly depressed over the lake. The lake–land breeze and the background vapour enriched by Lake Malawi drive primarily a diurnal variation in the surface moisture flux divergence/convergence over the lake and surrounding area which contributes to the diurnal cycle of precipitation in this region.

Diurnal Variations of Precipitation over North China Regulated by the Mountain-plains Solenoid and Boundary-layer Inertial Oscillation

The mountain-plains solenoid (MPS) and boundary-layer inertial oscillation (BLO) are two typical regional forcings at the diurnal time scale. Their relative role in regulating the diurnal variations of summer rainfall over North China and their change under different monsoon conditions are studied using a 19-yr archive of satellite rainfall and reanalysis data. It is shown that both a strong MPS and BLO can increase nocturnal rainfall in the North China plains but exhibit evident regional differences. The MPS-induced nocturnal rainfall is relatively confined to the plains adjacent to mountains from late night to morning, due to the upward branch of the nighttime MPS. In contrast, the BLO-induced nocturnal rainfall strengthens from early evening and is more extensive in early morning over the open plains further east. The contrasting effect in the evening is related to the convergent (divergent) easterly anomaly in the plains under the BLO (MPS). The BLO also induces the relatively strong enhancement of moisture convergence and high humidity by the southerly anomaly at late night. On strong monsoon days, the nocturnal rainfall amount associated with the MPS and BLO increases considerably in the plains. Both regional forcings become effective in regulating the rainfall diurnal cycle with enhanced moisture convergence under monsoon conditions. Their induced diurnal amplitudes of moisture convergence can be comparable to the daily mean by monsoon flow. The regional forcings thus couple with monsoon flow to strengthen rainfall in the plains, particularly from late night to morning. The results highlight that a combination of regional and large-scale forcings can strongly regulate the warm-season climate.

Diurnal Variations of Different Cloud Types and the Relationship between the Diurnal Variations of Clouds and Precipitation in Central and East China

In this paper, the diurnal variations of various clouds are analyzed using hourly cloud observations at weather stations in China from 1985 to 2011. In combination with merged hourly precipitation data, the relationship between the diurnal variations of clouds and precipitation in the summers from 2008 to 2011 are studied. The results show that the occurrence frequencies of total cloud and various cloud types exhibit significant diurnal variations. The diurnal variations of the occurrence frequencies of altocumulus and stratocumulus show a bimodal pattern, with peaks appearing in the early morning and late afternoon. The early morning peaks of altocumulus and stratocumulus appear earlier in the summer than in the other seasons, while the late afternoon maxima show an opposite trend. The occurrence frequency of nimbostratus peaks in the morning between 07 and 12 LST (local solar time), and the peak value lags 2 to 3 h from west to east along the Yangtze River valley; meanwhile, the diurnal variation shows no clear differences caused by changes in the latitude or seasons. Cumulus shows an afternoon (14 LST) maximum, while cumulonimbus peaks in the late afternoon during 16–20 LST, and both of them present a great diurnal range. Cirrus usually reaches its peak at 17–18 LST, and it differs by 1 to 2 h with a change in the latitude. The results of the study first show that the diurnal variations of precipitation among different regions are dominated by different clouds. The upper reaches of the Yangtze River valley present a midnight precipitation maximum that is mainly dominated by cumulonimbus. For the middle reaches of the Yangtze River valley impacted by nimbostratus, the precipitation peaks in the early morning. In South and Northeast China, the precipitation peaks in the afternoon and is determined by the diurnal variations of convective clouds. In the region between the Yangtze River valley and Yellow River valley, the precipitation peaks in the early morning and afternoon; the early morning peak is mainly determined by stratiform clouds, while the afternoon peak is closely related to convective clouds.

Effects of the Convective Triggering Process in a Cumulus Parameterization Scheme on the Diurnal Variation of Precipitation over East Asia

Effects of the convective triggering process in a cumulus parameterization scheme on the diurnal variation of precipitation over East Asia are examined using a regional climate model. Based on a cloud-resolving simulation showing the irrelevance of convective inhibition once convection is initiated and the sensitivity experiments to trigger conditions, the triggering process in the simplified Arakawa-Schubert (SAS) convection scheme is modified to use different convective initiation and termination conditions. The diurnal variation of precipitation frequency with the modified triggering process becomes in phase with the observed one, leading to a delayed afternoon peak in precipitation rate that is in better agreement with the observation. However, the bias in the phase of precipitation intensity is not resolved and the bias of excessive precipitation increases, indicating that adequate representation of not only the triggering process but also other moist convective processes that determine the strength of convection is required for further improvement in the simulation of the diurnal variation of precipitation.

Insights into the Summer Diurnal Cycle over Eastern South Africa

Abstract Adopting a state-of-the-art numerical model system, we investigate how the diurnal variations in precipitation and local breeze systems are characterized by lower-boundary conditions related to the Drakensberg highland and warm SST associated with the Agulhas Current. A control simulation can simulate the hydrometeorological climates in the region realistically, but the terrestrial rainfall is overestimated. During daytime, the precipitation is confined to the Drakensberg highland, and there is an onshore local breeze, while during midnight to morning, the rainfall is confined to the Agulhas Current, and the breeze is offshore. These variations are captured by the numerical simulation, although the timing of maximum rainfall is early over the land and delayed over the ocean. The sensitivity experiment in which the Drakensberg is absent shows a drastic modification in the diurnal variations over land and ocean. The terrestrial precipitation is largely decreased around the Drakensberg and is largest along the coast during daytime. The nocturnal marine precipitation along the Agulhas Current is also reduced. Although the daily residual breeze is still pronounced even without the Drakensberg, wind speed is weakened. We attribute this to the reduction of precipitation. In another sensitivity experiment with smoothened warm SST due to the Agulhas Current, the amplitudes of diurnal variations are not modified remarkably, but the coastal rainfall is diminished to some extent due to less evaporation along the Agulhas Current. This study concludes that the Drakensberg plays a crucial role for the diurnal cycle, and the impact of the Agulhas Current is limited on the diurnal cycle of the coastal precipitation in this region.

Classification and Diurnal Variations of Precipitation Echoes Observed by a C-band Vertically-Pointing Radar in Central Tibetan Plateau during TIPEX-III 2014-IOP

This study investigates classification and diurnal variations of the precipitation echoes over the central Tibetan Plateau based on the observations collected from a C-band vertically-pointing frequency-modulated continuous-wave (C-FMCW) radar during the Third Tibetan Plateau Atmospheric Scientific Experiment (TIPEX-III) 2014-Intensive Observation Period (2014-IOP). The results show that 51.32% of the vertical profiles have valid echoes with reflectivity > –10 dBZ, and 35.06% of the valid echo profiles produce precipitation at the ground (precipitation profiles); stratiform precipitation with an evident bright-band signature, weak convective precipitation, and strong convective precipitation account for 52.03%, 42.98%, and 4.99% of the precipitation profiles, respectively. About 59.84% of the precipitation occurs in the afternoon to midnight, while 40.16% of the precipitation with weaker intensity is observed in the nocturnal hours and in the morning. Diurnal variation of occurrence frequency of precipitation shows a major peak during 2100–2200 LST (local solar time) with 59.02% being the stratiform precipitation; the secondary peak appears during 1300–1400 LST with 59.71% being the weak convective precipitation; the strong convective precipitation occurs mostly (81.83%) in the afternoon and evening with two peaks over 1200–1300 and 1700–1800 LST, respectively. Starting from approximately 1100 LST, precipitation echoes develop with enhanced vertical air motion, elevated echo top, and increasing radar reflectivity. Intense upward air motion occurs most frequently in 1700–1800 LST with a secondary peak in 1100–1400 LST, while the tops of precipitation echoes and intense upward air motion reach their highest levels during 1600–1800 LST. The atmospheric conditions in the early morning are disadvantageous for convective initiation and development. Around noon, the convective available potential energy (CAPE) increases markedly, convective inhibition (CIN) is generally small, and a super-dry-adiabatic layer is present near the surface (0–400 m). In the early evening, some larger values of CAPE, level of neutral buoyancy, and total precipitable water are present, suggesting more favorable thermodynamic and water vapor conditions.

Role of the Nocturnal Low-level Jet in the Formation of the Morning Precipitation Peak over the Dabie Mountains

The diurnal variation of precipitation over the Dabie Mountains (DBM) in eastern China during the 2013 mei-yu season is investigated with forecasts of a regional convection-permitting model. Simulated precipitation is verified against surface rain-gauge observations. The observed morning precipitation peak on the windward (relative to the prevailing synoptic-scale wind) side of the DBM is reproduced with good spatial and temporal accuracy. The interaction between the DBM and a nocturnal boundary layer low-level jet (BLJ) due to the inertial oscillation mechanism is shown to be responsible for this precipitation peak. The BLJ is aligned with the lower-level southwesterly synoptic-scale flow that carries abundant moisture. The BLJ core is established at around 0200 LST upwind of the mountains. It moves towards the DBM and reaches maximum intensity at about 70 km ahead of the mountains. When the BLJ impinges upon the windward side of the DBM in the early morning, mechanical lifting of moist air leads to condensation and subsequent precipitation.

Effects of Long- and Short-Term Atmospheric Water Cycles on the Water Balance over the Maritime Continent

Abstract This study investigated atmospheric water cycles over several time scales to understand the maintenance processes that control heavy precipitation over the islands of the Maritime Continent. Large island regions can be divided into land, coastal, and ocean areas based on the characteristics of both the hydrologic cycle and the diurnal variation in precipitation. Within the Maritime Continent, the major islands of Borneo and New Guinea exhibit different hydrologic cycles. Large-scale circulation variations, such as the seasonal cycle and the Madden–Julian oscillation, have a lesser effect on the hydrologic cycle over Borneo than over New Guinea because the effects depend on their shapes and locations. The impact of diurnal variations on both regional-scale circulation and water exchange between land and coastal regions is pronounced over both islands. The recycling ratio of precipitation, which can be related to stronger diurnal variation in the atmospheric water cycle that results from enhanced evapotranspiration over tropical rain forests, is higher over Borneo than over New Guinea.

An Observational Study of the Diurnal Variation of Precipitation over Hong Kong and the Underlying Processes

AbstractHourly rainfall from automatic weather stations and reanalysis data from MERRA-2 are used to investigate the diurnal variation of precipitation in Hong Kong, a site along the southeast China coast with strong interactions between the monsoonal circulation and the land–sea breeze. The precipitation in Hong Kong is characterized by a spatially uniform diurnal cycle with the peak at about 0800 local time (LT), with rather weak dependence on local terrain. Precipitation unrelated to tropical cyclones (TCs) dominates the diurnal variation of precipitation, especially in the summer. The diurnal cycle exhibits a notable seasonal dependence, with the strongest signal in the summer. The morning peak of precipitation over Hong Kong is coincident with deep rising motion, linking to near-surface convergence and overlying weak divergence. The convergence may be attributed to the prevalence of the southerly monsoonal flow over the South China Sea (SCS) and to the northerly land breeze induced by the land–sea thermal contrast in the morning. The overlying weak divergence could be ascribed to the nocturnal–early morning acceleration of southerly flow over southeast China. Linked to the inverse relationship between monsoon intensity and the land–sea thermal contrast, the diurnal cycle of precipitation is strengthened when the SCS monsoon is active and weakened when the land–sea thermal contrast is high. Both the cloud-top radiative cooling effect and the enhanced radiative cooling over inland cloud-free areas also play roles in the development of the morning rainfall peak over Hong Kong.

Evaluation of diurnal variation of GPM IMERG‐derived summer precipitation over the contiguous US using MRMS data

This paper investigates the accuracy of the Integrated Multi‐satellitE Retrievals for Global Precipitation Measurement (GPM), which provides merged microwave and infrared satellite precipitation estimates, over the contiguous US. The study focuses on diurnal variations in precipitation during a two‐year summer period (June–August, 2014–2015). The normalized amplitude and phase of the diurnal cycle of IMERG are evaluated against those of ground reference from the Multi‐Radar/Multi‐Sensor system in terms of precipitation amount, frequency and intensity on a 1°/1 hr scale. IMERG well captures large‐scale regional features of the diurnal cycle of precipitation and overall agrees well with the reference for both diurnal and semidiurnal variations. The comparison results indicate that the IMERG precipitation estimates can be a reliable alternative to ground‐based measurements even at the subdaily scale; however, region‐specific data discrepancies are still observed. For instance, we reveal that IMERG substantially overestimates normalized amplitude of diurnal precipitation in the central US, while IMERG tends to underestimate diurnal variations over the mountain regions in the western and eastern US. In terms of phase, we find a significant difference in the timing of peak precipitation between convective and stratiform regions of mesoscale convective systems (MCSs) over the Great Plains. This time shift is more apparent during the mature and dissipation stages of MCSs, which lead to relatively early peaks in the diurnal cycle of precipitation from IMERG. This phase bias implies a higher sensitivity of IMERG towards the convective regions of MCSs, supposedly because of the brightness temperature depression coming from ice particles aloft sampled by spaceborne passive microwave sensors. Such discrepancy between the actual and satellite‐estimated precipitation timing can be challenging, e.g. when the satellite data are used to study subdaily precipitation processes or to validate numerical simulations. Consequently, our assessment of the IMERG performances highlights the need for improvements in the IMERG system.

Evaluation of Real‐Time Convection‐Permitting Precipitation Forecasts in China During the 2013–2014 Summer Season

AbstractForecasts at a 4 km convection‐permitting resolution over China during the summer season have been produced with the Weather Research and Forecasting model at Nanjing University since 2013. Precipitation forecasts from 2013 to 2014 are evaluated with dense rain gauge observations and compared with operational global model forecasts. Overall, the 4 km forecasts show very good agreement with observations over most parts of China, outperforming global forecasts in terms of spatial distribution, intensity, and diurnal variation. Quantitative evaluations with the Gilbert skill score further confirm the better performance of the 4 km forecasts over global forecasts for heavy precipitation, especially for the thresholds of 100 and 150 mm d−1. Besides bulk characteristics, the representations of some unique features of summer precipitation in China under the influence of the East Asian summer monsoon are further evaluated. These include the northward progression and southward retreat of the main rainband through the summer season, the diurnal variations of precipitation, and the meridional and zonal propagation of precipitation episodes associated with background synoptic flow and the embedded mesoscale convective systems. The 4 km forecast is able to faithfully reproduce most of the features while overprediction of afternoon convection near the southern China coast is found to be a main deficiency that requires further investigations.