Diurnal Cycle Of Rainfall Research Articles

Synoptic Influences on the Diurnal Cycle of Rainfall over Western Puerto Rico

Abstract The objective of this study is to understand rainfall processes over tropical islands by identifying synoptic conditions that influence the diurnal cycle of rainfall over western Puerto Rico. Summer rainfall over Puerto Rico is dominated by its afternoon peak, yet there is large variability in its behavior that remains challenging to predict. We use radiosonde and airborne data collected through the NASA Convective Processes Experiment—Aerosols and Winds (CPEX-AW) field campaign (August–September 2021) to achieve our objective, in addition to the network of surface station data over the island. We find that the background wind speed and humidity have strong influences on afternoon rainfall through different mechanisms. A stronger background wind inhibits afternoon rainfall likely by reducing land–sea thermal contrast and weakening sea-breeze convergence over the island. At the same time, an inversion layer often forms with a stronger background wind that further inhibits deep convection. When the background wind is weak and sea breezes are prominent, afternoon rainfall increases exclusively over the island, while limited rainfall appears over the surrounding ocean. However, enhanced rainfall still occurs over the island with weak sea breezes if humidity is high, accompanied by enhanced rainfall over the surrounding ocean due to the offshore movement and development of convective storms. The sources of variability in background wind and humidity are mostly independent, resulting in a wide range of synoptic conditions and associated effects on the island rainfall. This expanded understanding of the mechanisms causing variability of diurnal rainfall can lead to improved forecasts over Puerto Rico and other tropical islands.

Impacts of the new UM convection scheme, CoMorph-A, over the Indo-Pacific and Australian regions

A new convection scheme, ‘CoMorph-A’, has been introduced into the latest UK Met Office coupled (GC4) and atmosphere-only (GA8) models. In this study, the impact of CoMorph-A is assessed in atmosphere-only Atmospheric Model Intercomparison Project simulations, as well as in sets of initialised 28-day forecasts with both the coupled and uncoupled models. Initial results show improvements over the Indo-Pacific and northern Australian regions, as well as improvements in the rainfall bias, Madden–Julian Oscillation simulation and prediction, tropical cyclone forecasts and the diurnal cycle of rainfall over the Maritime Continent. The improvements are mostly consistent across the initialised forecasts and the climate simulations, indicating the effectiveness of the new scheme across applications. The use of this new convection scheme is promising for future model configurations, and for improving the simulation and prediction of Australian weather and climate. The UK Met Office is continuing to develop CoMorph and will soon release version B.

Topoclimate and diurnal cycle of summer rain over the Ethiopian highlands in a convection‐permitting simulation

AbstractTopoclimate, orographically enhanced rain on windward slopes and leeward rain shadows, control rainfall variability in tropical mountains. Such variability may cause a substantial societal impact in populated highlands such as in Ethiopia. This study aims at understanding the rainfall diurnal cycle and the orographic driving factors over the Ethiopian highlands using the ALARO‐0 regional climate model at convection‐permitting resolution, over a period of 21 years. While the evaluation against satellite‐based observations shows a too early onset of the model diurnal cycle and a too low nocturnal rainfall, several conclusions can be drawn from the model simulations presented here. Elevation is the most important determining factor for modelled rainfall with increased average rainfall and rainfall per rainfall event towards higher elevations. Ethiopia's simulated summer rain exhibits a pronounced diurnal cycle with the highest rainfall occurring during the early afternoon hours and the minimum values occurring in the late night. Average rainfall and rainfall per rainfall event are substantially larger on the windward sides than on the leeward sides of the mountains, except during the peak hours. The diurnal cycles of temperature and humidity start earlier in the morning and recede later than the cycles of wind speed and rainfall. Moreover, rainfall peaks occur earlier in the day at higher elevations, and at night in valleys and in Afar Triangle. Rain intensities around noon on the leeward side are slightly higher than those on the windward side of the highest mountains (>3000 m). This could be due to delayed onset of cloudiness and larger morning insolation on the leeward side of the mountain, but this needs further study. The prevalence of windward over leeward rainfall, the stark contrast in wind‐speed diurnal cycle between windward and leeward slopes, and the early peak hour of surface air and dew point temperature all point towards temperature‐induced rather than wind‐induced convection. These differences are likely to determine hydrology and vegetation distribution, and farmers economy at large. Hence, the need for a way out from the ‘one‐size‐fits‐all’ agro‐ecosystem management approach towards a site‐specific policy that takes into account climatic differences.

Can Sub‐Daily Multivariate Bias Correction of Regional Climate Model Boundary Conditions Improve Simulation of the Diurnal Precipitation Cycle?

AbstractThe diurnal cycle is often poorly reproduced in global climate model (GCM) simulations, particularly in terms of rainfall frequency and amplitude. While improvements in the regional climate model (RCM) with bias‐corrected boundaries have been reported in previous studies, they assumed that diurnal patterns are simulated correctly by the GCM, potentially leading to inaccuracies in the maximum rainfall timing and magnitude within the RCM domain. Here we provide the first examination of improvements to the diurnal cycle, within a RCM domain, achieved through the use of sophisticated bias‐corrected lateral and lower boundary conditions. Results show that the RCMs with bias‐corrected boundaries generally present improvement in capturing both rainfall timing and magnitude, particularly in northern Australia, where a strong diurnal pattern in rainfall is prevalent. We show that correcting systematic sub‐daily multivariate bias in RCM boundaries improves the diurnal rainfall cycle, which is particularly important in regions where short‐term intense precipitation occurs.

The Diurnal Cycle of Rainfall and Deep Convective Clouds Around Sumatra and the Associated MJO‐Induced Variability During Austral Summer in Himawari‐8

AbstractThe effects of the diurnal cycle and large‐scale atmospheric disturbances dominate rainfall and cloud variability in the Maritime Continent. This study examines the modulation of the Austral Summer diurnal cycle by the Madden–Julian Oscillation (MJO) using cloud populations through precipitation and deep convective cloud derived from satellite measurements. Using Rainfall Potential Areas from Himawari‐8 Advanced Himawari Imager as a proxy for deep convection, our analysis shows that convective clouds are present ∼55% of the time over land in Sumatra during the afternoon and night. Cloud signatures reveal semi‐diurnal structures of deep convective clouds off the West Coast of Sumatra. In contrast, the East Coast exhibits explicit sea‐ward propagation patterns of deep convective controlled by the coastal effects around the Strait of Malacca and Java Sea, together with the influence of synchronized diurnal forcing between islands. We show that the MJO drives the enhanced convective phases, changing the cloud top type distribution, moisture convergence, and moisture transport over the equatorial Indian Ocean. The cold cloud area also increases during the MJO active phases, which is linked to frequent deep convective cloud development near the mountain ranges of Sumatra and the adjacent ocean. The analyses of cloud variations based on the rainfall potential areas and cloud top type provide evidence of the effects of convective processes on the diurnal cycle of ice and water vapor distribution in the troposphere.

Tropical Easterly Waves Over Costa Rica and Their Relationship to the Diurnal Cycle of Rainfall

AbstractUsing an index of tropical easterly wave (TEW) activity derived from spacetime‐filtered outgoing longwave radiation, we construct composites of long‐term hourly surface meteorological observations and morningtime sounding data collected near San José, Costa Rica to investigate how TEWs affect the diurnal cycle of rainfall over land. Our results indicate that TEWs enhance the frequency of occurrence of rain during convectively active conditions over the course of the diurnal cycle. By contrast, rainfall conditional intensity sensitivity to TEW phase appears more nuanced, with indications that active conditions induce a slight delay in the timing of the diurnal peak intensity but a longer duration of heavier rainfall. Analysis of associated hourly surface meteorology along with sounding profiles and derived thermodynamic parameters points to both initial vertical and time‐evolving surface conditions regulating diurnal behavior, such as greater instability and higher precipitable water in morningtime profiles under active phase conditions.

The role of the Kuroshio Current on the diurnal cycle of Meiyu-Baiu rainband in mid-June

This study investigated the mechanism of the strong diurnal cycle of precipitation over the Kuroshio Current (KC) in mid-June when the climatological location of the Meiyu-Baiu (MB) front is aligned with the KC. The diurnal cycle of precipitation exhibits double peaks, with the primary peak in the morning (03–12 LST) and the secondary peak in the afternoon (12–15 LST). It was revealed that the morning peak is induced by convective instability associated with the large temperature difference between the sea surface and the surface air (TDiff), whereas the cross-frontal circulation is responsible for the afternoon peak. In the morning, heating from the KC intensifies as the TDiff maximizes. Intensified convective instability due to the enhanced heating from the KC increases the mean amount of convective precipitation (CP) as well as the probability of stronger CP. The surface wind convergence and the confluence sustaining the convection intensify the frontogenesis, which leads to the maximization of the frontal intensity in the afternoon. The afternoon peak of precipitation is in accordance with the intensified MB front and the associated cross-frontal circulation. However, direct contribution of diabatic heating to the frontogenesis is relatively weak. This study provides a physical understanding of the intensified diurnal cycle of MB rainfall in terms of the interaction between oceanic and atmospheric fronts, the KC and MB, respectively.

Principal Modes of Diurnal Cycle of Rainfall over South China during the Presummer Rainy Season

Abstract The principal modes of the diurnal cycle of rainfall (DCR) over South China during the presummer rainy season are examined using 23-yr satellite observations and reanalysis data. Three distinctly different DCR modes are identified via empirical orthogonal function analysis, that is, the early-afternoon precipitation (EAP) mode, the late-afternoon precipitation (LAP) mode, and the morning precipitation (MP) mode. Under the EAP mode, the rainfall starts to increase from midnight and reaches its peak in the early afternoon. The nocturnal to morning rainfall generally concentrates on the northeastern Pearl River delta (PRD) and along the coastline. The coastal rainfall is initiated from the convergence zone induced by the strong onshore wind and is further enhanced via the establishment of a land breeze in the early morning. The northeastern PRD center is mainly attributed to the windward mechanical lifting associated with the strong low-level wind. The afternoon rainfall is pronounced over inland areas and exhibits significantly regional diversity. The eastern inland rainfall develops from the early-morning rainfall over the northeastern PRD, whereas the eastward-propagating rain belts associated with frontal activities are responsible for the formation of western inland rainfall. The LAP mode features a late-afternoon peak, which is triggered and developed locally with favorable thermal–dynamic conditions over western inland South China. The MP mode exhibits a single early-morning peak. Nocturnal to morning rainfall is prominent on the northeastern PRD and near-offshore region. The near-offshore rainfall is basically induced by the convergence between the onshore wind and land breeze in the early morning, which further propagates far offshore in the morning due to effects of gravity waves.

Dynamic and thermodynamic processes related to precipitation diurnal cycle simulated by GRIST

Most state-of-the-art general circulation models cannot well simulate the diurnal cycle of precipitation, especially the nocturnal rainfall peak over land. This study assesses the diurnal cycle of precipitation simulated using the Global-to-Regional Integrated forecast SysTem (GRIST) in its numerical weather prediction (NWP) configuration at resolutions typical of current global climate models. In the refinement region, the variable-resolution model well distinguishes the distinct features of diurnal cycle. No apparent artificial features are observed in the transition zone of the variable-resolution mesh. The model also exhibits a similar diurnal cycle pattern to the observation in the coarse-resolution region. We further investigate the model behaviors of dynamics–physics interaction by analyzing hourly dynamical and thermodynamical diagnostics. Composite analysis based on rainfall peak time is applied to examine the model capability in distinguishing different precipitation processes of daytime and nighttime peaks. Over East Asia, the model well reproduces both the nocturnal-to-early-morning and the afternoon rainfall peaks. The model simulates the dominant contribution of large-scale upward moisture advection to the formation of stratiform-like rainfall peaks, and produces daytime surface-heating induced rainfall. Refinement of the resolution substantially increases the composited nighttime precipitation intensity but has little impact on the composite percentage. The model captures the realistic dynamical and thermodynamical conditions for the occurrence of nocturnal rainfall. These results demonstrate that the variable-resolution model is able to reproduce the diurnal cycle of climatological summer rainfall through realistic precipitation processes.

Observing the Diurnal Cycle of Coastal Rainfall over Western Puerto Rico in Collaboration with University of Puerto Rico Students

Abstract The diurnal cycle of coastal rainfall over western Puerto Rico was studied with high-frequency radiosondes launched by undergraduate students at the University of Puerto Rico at Mayagüez (UPRM). Thirty radiosondes were launched during a 3-week period as part of NASA’s Convective Processes Experiment—Aerosols and Winds (CPEX-AW) field project. The objective of the radiosonde launches over Puerto Rico was to understand the evolution of coastal convective systems that are often challenging to predict. Four different events were sampled: 1) a short-lived rainfall event during a Saharan air dust outbreak, 2) a 2-day period of limited rainfall activity under northeasterly wind conditions, 3) a 2-day period of heavy rainfall over land, and 4) a 2-day period of long-lived rainfall events that initiated over land and propagated offshore during the evening hours. The radiosondes captured the sea-breeze onset during the midmorning hours, an erosion of lower-tropospheric inversions, and substantial differences in column humidity between the four events. All radiosondes were launched by volunteer undergraduate students who were able to participate in person, while the coordination was done virtually with lead scientists located in Puerto Rico, Oklahoma, and Saint Croix. Overall, this initiative highlighted the importance of student–scientist collaboration in collecting critical observations to better understand complex atmospheric processes.

Sea Surface Temperature Impact on Diurnal Cycle and Seasonal Evolution of the Guinea Coast Rainfall in Boreal Spring and Summer

Abstract ERA5 reanalyses and observations of convective clouds and precipitation are used over the northern Gulf of Guinea between 7°W and 3°E to study the influence of ocean surface temperature and the land–sea temperature gradient on Guinea Coast rainfall (GCR) in boreal spring and summer. Seasonal composites are calculated around two dates indexing the onset (Tref) and demise (Tend) of the GCR. The Tref date corresponds to the emergence of the equatorial upwelling in boreal spring, which “pushes” the zonal precipitation belt northward against the Guinea coast. The Tend date characterizes the emergence of the coastal upwelling in July, which is known to coincide with the beginning of the “Little Dry Season” that lasts until September. Along the Guinea Coast, the diurnal cycle of the air–sea temperature gradient controls precipitation through the land–sea breeze, which explains why precipitation reaches its maximum around noon over the ocean, and in the late afternoon over the continent. The emergence of the Guinea Coast upwelling in July induces a weakening of southerlies on a seasonal scale, and a weaker land breeze on a diurnal scale. It induces a decrease in the convergence of humidity transport across the coast and in coastal oceanic precipitation. Therefore, the GCR is seasonally controlled by the latitude of the maximum tropospheric water vapor content and the annual cycle of the West African monsoon, but the ocean surface temperature is responsible for the abruptness of its onset via the intensification of the equatorial upwelling around the end of May, and possibly of its demise as well via the emergence of the coastal upwelling by early July.

Diurnal Variation of Precipitation over the High Mountain Asia: Spatial Distribution and Its Seasonality

Abstract Using abundant rainfall gauge measurements and Global Precipitation Mission (GPM) data, spatial patterns of rainfall diurnal cycles and their seasonality over high mountain Asia (HMA) were examined. Spatial distributions of rainfall diurnal cycles over the HMA have a prominent seasonality regulated by circulations at different spatiotemporal scales, within which large regional contrasts are embedded. Rainfall diurnal variability is relatively weak in the premonsoon season, with larger amplitude over the western HMA, the southeastern HMA, as well as southern periphery regions, characterized by a dominant late afternoon to morning rainfall preference. The pattern of rainfall spatial distributions is closely related to the midlatitude westerlies. Both the mean rainfall and amplitudes of diurnal cycles become more pronounced with the advance of monsoon season but weaken during postmonsoon. The widespread late afternoon to night pattern over HMA migrating with seasonal atmospheric circulation is consistent with the lifetime of convective systems, which become active from the afternoon due to radiative heating and decay during the night. Stationary terrain-dependent night-to-morning rainfall patterns are visible in those east–west-orientated valleys over HMA and the Qaidam basin throughout the seasons. This salient geographical dependence is associated with local circulation produced by the strong differential thermal conditions over mountains and valleys, which can lift the warm moist air at the mouth of the valley and trigger nocturnal convection. Significance Statement The main purpose of this study is to explore how spatial patterns of rainfall diurnal cycles over high mountain Asia vary with the seasons. Our results show that the widespread late afternoon to night rainfall over high mountain Asia migrating with seasonal atmospheric circulation is consistent with the lifetime of convective systems. Stationary terrain-dependent night-to-morning rainfall patterns are visible in those east–west-orientated valleys over high mountain Asia and the Qaidam basin throughout the seasons. These results highlight the importance of large-scale atmospheric circulation and local circulation on precipitation, which is critical for water resources over high mountain Asia.

Analysis of Diurnal Evolution of Cloud Properties and Convection Tracking over the South China Coastal Area

Different diurnal rainfall cycles occur over the offshore and inland regions of the South China coastal area (SCCA). Inspired by these findings, in this study, we investigated the diurnal evolution features of cloud systems and cloud properties inside such systems for both the SCCA offshore and inland regions, using cloud data retrieved from a recently developed deep neural network model. Rainy day data for June 2017 revealed that the ice cloud optical thickness and top height reached their peak intensities at noon (~12 local standard time (LST)) over the offshore region, approximately 2 h later than the rainfall peak. Over the inland region, cloud and rainfall peaks simultaneously appeared from ~18 to 20 LST. When further examining the cloud-amount variation of different ice-cloud types, we found a clear diurnal oscillation in the medium-thick cloud amount over the offshore region, while for the inland region, this cloud type had no obvious diurnal peak, showing a low cloud amount throughout the day. This phenomenon suggests different inner structures and intensities between offshore and inland convections. To better elucidate the convection features over different regions, a tracking algorithm was applied to obtain various parameters, such as size, number, and duration of mesoscale convective systems. The strongest convections, which lasted over 12 h, tended to be abundant over the offshore region from ~03 to 12 LST, and an inland to offshore migration at ~03 LST was facilitated by the beneficial meteorological conditions observed at 113–116˚E, 20.5–22.5˚N.

Froude‐number‐based rainfall regimes over the Western Ghats mountains of India

AbstractVariations in the character of monsoonal rainfall over the Western Ghats region on the west coast of India are studied using radiosondes, satellite observations, and reanalysis products. Summer monsoon rainfall over this region occurs in alternate offshore and onshore phases. It is shown that these phases are controlled primarily by the strength of the low‐level westerly jet. Thus, a classification based on the Froude number, , of the onshore flow is proposed, where, is the mountain height, is the mean wind speed, and is the mean Brunt–Väisäla frequency over depth . At low (< 0.5), onshore winds are weak and the diurnal thermal fluctuation over the orography is strong; the land–sea and mountain–valley circulations are enhanced, leading to a stronger diurnal control over the rainfall. A nocturnal offshore propagation of rainfall from the west coast is seen during this phase. Rainfall over the rainshadow region to the east of the Western Ghats also increases, due to a weaker lee effect, while it decreases over the Western Ghats, due to a greater blocking effect. At high (> 1), orographic blocking of the low‐level winds is weak. Thus, rainfall is enhanced over the Western Ghats and reduced over the rainshadow region due to a stronger lee effect. In this phase, the diurnal thermal fluctuation over the orography is weak. The bulk Richardson number is less than 1, suggesting a dominance of vertical wind shear over the buoyancy forces. The level of free convection and convective inhibition over the west coast are also very low. Hence, at high , rainfall over the west coast results mainly from mechanical uplifting of the westerly winds by the Western Ghats, with no preference for a particular time of day. These findings will help in improving the representation of orographic effects and the diurnal cycle of rainfall in numerical models.

Hydroclimatology and Hydrometeorology of Flooding Over the Eastern Tibetan Plateau

AbstractThe hydroclimatology and hydrometeorology of flooding over the Third Pole region is poorly understood, despite its societal and environmental significance. Here we examine extreme rainfall and flooding over the eastern Tibetan Plateau (TP) based on empirical analyses of long‐term, in‐situ rainfall and stream gaging observations as well as the ECMWF Reanalysis fields. We develop a flood catalog that consists of 168 extreme rainfall‐runoff floods over the eastern TP, and characterize the synoptic conditions for flood‐producing storms based on the principal component analysis. We show the transitional pattern form Asian summer monsoons to midlatitude systems as the most frequent synoptic conditions for flooding over the eastern TP. The interplay between complex terrains and moisture transport determines the contrasting flood characteristics (in terms of intensity and spatial pattern) under different synoptic environments. We carry out high‐resolution Weather Research and Forecasting modeling analysis for four flood‐producing storms over the eastern TP. We highlight the interaction of complex terrains and nocturnal low level jets as the key mesoscale ingredients in dictating a pronounced diurnal cycle of extreme rainfall over the southeastern portion of TP. Our results establish the link between large‐scale synoptic environment, mesoscale process, and regional flood hydrology over the eastern TP, and therefore contribute to improved flood risk management practices over the Third Pole region under a changing climate.

Intraseasonal Change in Diurnal Cycle of Precipitation over Sumatra from IMERG Observation

This study investigates the intraseasonal change in the diurnal cycle of rainfall over Sumatra in terms of Madden Julian oscillation (MJO) phases. Change in the peak time of mean accumulation (PA), frequency (PF), and intensity (PI) of precipitation from Integrated Multi-Satellite Retrievals of GPM (IMERG) final run product version 06 data during 2016-2019 was investigated. Data were classified into active (2,3,4, and 5) and inactive (1,6,7 and 8) MJO. Rainfall in the Sumatra region is generally dominated by short rainfall duration, as found by a previous study. During the active MJO, the increase the number of rain events over the mainland Sumatra is dominated by rain lasting less than 6 h. In the Indian Ocean region, the increase in rain events is dominated by short and long-duration rain. The means of PA and PF during the active MJO showed a significant increase (0.4 mm/h and 10%), especially in the western part of Sumatra. On the other hand, the average PI during the active MJO tends to decrease (~ 1.5 mm/h), especially in the southern mainland of Sumatra. Finally, we found no significant change in the peak time of PA, PF, and PI during the active MJO and inactive MJO.

Meteorological Observation in the Central Kathmandu Valley using the First Automated Meteorological Observatory of Tri-Chandra Multiple Campus

The main meteorological features of the central Kathmandu valley, Nepal were investigated by means of the dataset recorded by the automated meteorological observatory of Tri-Chandra Multiple Campus (1295m a.s.l. and 27.708217oN, and 85.315369oE) from May 2018 to April 2021. Initially, this observatory was installed for laboratory work with promoting clean energy resources by phasing out mercury instruments, since the onset of the coronavirus pandemic the growing importance of having resilience in the meteorological observation system has been more clearly demonstrated. Now, this automated real-time meteorological observatory becomes a backbone of our academic system, whereby students and teachers can have direct access to the data source and can self-analyze the prevailing atmospheric condition. As the detailed picture of the seasonal and diurnal cycle of meteorological parameters over the central Kathmandu valley, Ranipokhari premises, has been unavailable, this study tries to outline the prevailing surface air condition more precisely. The analysis was made on the basis of seasonal and diurnal variations of the weekly and monthly mean of meteorological parameters. The results confirmed that the surface heating by solar radiation mainly drives the variation in surface meteorological parameters. It was observed that the daily minimum temperature is recorded just before dawn and a maximum by mid-day with lagging to the daily solar maxima. In the time, the relative humidity was derived in a reverse cyclic pattern. During the summer monsoon and winter monsoon season, when the diurnal range of solar intensity became lower, also the temperature, relative humidity, and wind strength possessed a smaller diurnal range. The seasonal rainfall distribution in central Kathmandu valley also agreed with the climatic normal, about 80% of the total annual rainfall is solely contributed by the summer monsoon season. Summer monsoon possesses some incoherent phase pattern of the diurnal cycle of mean rainfall with two comparable peaks, one as mid-night/nocturnal maxima and the other as of late afternoon maxima. While, the early morning rainfall intensity tends to decrease and attains its minima around late morning, whereby, the frequency of drizzle type of rainfall was most dominant.

Diurnal Rainfall Response to the Physiological and Radiative Effects of CO2 in Tropical Forests in the Energy Exascale Earth System Model v1

AbstractUnderstanding how the connection between rainfall and tropical forests will respond to increasing CO2 concentrations is a key element in understanding how the tropical water cycle will respond to increasing CO2. The plant physiological and radiative impacts of CO2 on rainfall patterns over tropical forest regions are examined in the Energy Exascale Earth System Model version 1.1 (E3SMv1.1‐BGC) biogeochemistry experiments. Composite analysis reveals a dampening of the diurnal cycle of rainfall over the Amazon, Congo, and Maritime Continent in response to rising CO2 levels, regardless of the sign of total rainfall change. A full factorial model experiment confirms that the CO2 radiative and CO2 plant physiological effects can individually or jointly reduce the magnitude of the rainfall diurnal cycle, though the physical pathway giving rise to the reduction differs between the two effects. For the physiological response, stomatal closure reduces evapotranspiration, which dries the boundary layer and raises the lifting condensation level. These effects combine to reduce deep convective rainfall during its peak occurrence in the late daytime to early nighttime period. For the radiative response, a relative reduction in daytime Convective Available Potential Energy (consistent with a reduction in the diurnal temperature range) leads to less frequent triggering of deep convection and a reduction of rainfall diurnal amplitude. These diurnal rainfall changes are structurally similar across seasons, and show little sensitivity to representation of nutrient coupling for the land biogeochemistry. In agreement with previous findings, the physiological response has only minor impact on extreme rainfall relative to the radiative response.

Diurnal variability of rain and rain-induced propagation impacts at a tropical location: A seasonal comparison

The knowledge of diurnal cycle of rainfall (DCR), is crucial for meticulous understanding of the rain climatology, and thus quite imperative for devising precise rainfall forecasting models which is important for future satellite communication channel modelling. The location of Kolkata is characterized by stratiform, convective as well as mixed type of rainfall during different seasons of the year. The rain diversity prevailing over Kolkata, located at the verge of the tropics, prompts critical investigation of rain and rain-induced impairments. The present study utilizes 4 years data of ground-based observations over Kolkata. The present study not only highlights significant features of DCR during the pre-monsoon and the monsoon days but also indicates the distinct variability of rain-induced propagation impairments associated with the rain drop size distribution pattern.

Diurnal rainfall cycle on small tropical island as seen by the 20 years half-hourly GPM-IMERG Satellite precipitation product

The diurnal rainfall cycle is one of the dominant factors causing the high variability of convection activity in the Indonesian Maritime Continent (IMC) and vulnerable to climate change. Research on diurnal rainfall cycles in small tropical islands (areas less than 6150 km2), such as in the IMC is important because of the lack of understanding of its characteristics. The aims of current study are to investigate spatial characteristics of the diurnal rainfall cycle over Bali and their surrounding islands using half-hourly rainfall that estimated from the Integrated Multi-satellitE Retrievals for GPM (IMERG) for the period 2001-2020. Statistical scores employed to analyse the diurnal rainfall cycle characteristics is means analysis that done during year observation on long-term half-hourly and annually. The result of half-hourly IMERG rainfall estimation confirms for the first time that the rainfall in Bali contributes to the diurnal rainfall variability over the eastern part of Java Island. In Bali, rainfall start to initiate during 1200 local time (LT, +8 UTC) mostly began in high elevation located in the central part of the island, on the southern slopes of the mountain range. Rainfall over land continues to increase and slightly spread to the west until reaches its peak in 1400 LT. Rainfall began to depletion in the central of the island and at 1530 LT spread toward the western and merged with the existing rainfall in the east of Java Island. In the night (2200 LT), rainfall leaves Bali island towards the Bali strait and Bali sea.