Phases Of Indian Summer Monsoon Research Articles

Clustering of low-pressure systems during the active phase of Indian summer monsoon in climate models

Clustering of low-pressure systems during the active phase of Indian summer monsoon in climate models

A Mechanism for the Summer Monsoon Precipitation Variability Over Northwest India Driven by Moisture Deficit Transport

AbstractA large reservoir of saturation deficit air is known to exist over the northern Arabian Sea and the adjoining land regions during the peak of Indian summer monsoon (ISM). The strengthening of monsoon low‐level jet (LLJ) in the northern parts of the Arabian Sea during the break phase of ISM helps in transporting this dry air toward northwestern India. Here, we show that, a weakening (strengthening) of the zonal flow over the northern Arabian Sea can reduce (enhance) the influx of the unsaturated air to the Northwest India and thereby enhance (reduce) precipitation there. The variability in the zonal flow over the northern Arabian Sea is a direct geostrophic response to the variability in the meridional pressure gradient over the Northwest India. The interannual variability in the mean sea level pressure over the region explains the inter‐annual variability of ISM precipitation during July–August over northwestern India. The contribution of El Niño Southern Oscillation in the interannual variability of precipitation over this region is not significant.

Reconstructing the pattern of late Quaternary climate through sediment-landform assemblages in the Dhauli Ganga valley (upper Ganga catchment), India

The present study focuses on the reconstruction of the pattern of late Quaternary climate variability through sediment-landform assemblages in the monsoon-dominated Dhauli Ganga valley. The South Tibet Detachment System (STDS) is a major litho-tectonic boundary that divides the Dhauli Ganga valley into two broad geomorphic entities. Towards the north of STDS, the valley is wide and “U” shaped, and the rivers have a braid-meandering channel, implying that the valley was carved by glacial sculpturing in the past. Whereas in the south, deep gorges indicate the dominance of fluvial processes. Based on the stratigraphic position and optical chronologies, the lithified moraines were assigned to Marine Isotopic Stage-3 (MIS-3) they were followed by a major deglaciation event represented by moderately lithified outwash gravels. Following this, a second glacier advance of lesser magnitude is dated 21.3 ± 2.2 ka, corresponding to the Last Glacial Maximum (LGM). A gradual recession of the LGM moraines led to the formation of a proglacial lake which probably persisted until around the onset of a pulsating deglaciation stage represented by outwash gravels dated between 13.4 ± 1.6 and 9.4 ± 0.8 ka. This was also the period when the valleys were overwhelmed by a high sediment water ratio, as indicated by temporary impoundments dated between 15.0 ± 1 ka and 10.0 ± 1 ka. Alluvial fan and debris flow sedimentation overwhelm the valley after around 9 ka and continues till the present.Climatically, the older lithified moraines indicate that glaciers advanced during the cooler MIS-4 or MIS-3. The first major deglaciation event seems to represent the pluvial phase of MIS-3. The presence of LGM moraines indicate that the valley responded to the global cooling and associated enhanced westerlies. In contrast, the chronology of outwash gravels suggests that the valley witnessed insolation driven by the early Holocene strengthened Indian Summer Monsoon (ISM). The undated youngest alluvial fans/debris flows are assigned the mid to late Holocene age (<9.5 ka) and seem to have deposited during the declining phase of ISM (low solar insolation). The study suggests that the landform evolution responded to both the global and regional climate variability indicating the sensitivity of the paraglacial valleys in the monsoon-dominated region to the late Quaternary climate variability.

Tracing the convective sources of air at tropical tropopause during the active and break phases of Indian summer monsoon

Tracing the convective sources of air at tropical tropopause during the active and break phases of Indian summer monsoon

Review of speleothem records of the late Holocene: Indian summer monsoon variability & interplay between the solar and oceanic forcing

Indian summer monsoon (ISM) variability in the late Holocene (last 4000 years) is of great interest as the arid phase of ISM and cultivation of kharif (rainy season) crops started in this period. The present study aims to revisit the available speleothem records to study ISM rainfall variations and possible controlling factors in different Indian regions viz., core monsoon zone (CMZ), peninsular, the Himalaya, and the Bay of Bengal in the last 4000 years. The late Holocene encompasses notable global warm periods viz., Medieval Climate Anomaly, Roman Warm Period (RWP) & Minoan Warm Period, and cold periods viz., Dark Age cold period and Little Ice Age (LIA). ISM rainfall declines until the middle of RWP in all the regions. The decline is linked with the southward migration of the Intertropical convergence zone caused by the northern Hemisphere summer insolation. Though the Solar insolation follows the same trend, all the records show large variability with the disappearance of the declining trend around the middle of RWP. This change coincided with the reversal in the north Atlantic Sea surface temperature (SST) trend, northern hemisphere temperature, and abrupt changes in the southeastern Indian Ocean SST. This period also witnessed high El-Nino Southern Oscillation activities. This synergy of ISM variations in the characterized zones falls apart during the pre-LIA with a slight increasing (decreasing) trend in CMZ and Bay of Bengal (peninsular and Himalayan). The spatially variable response of ISM rainfall in recent centuries might be caused by the interaction between internal variability and external forcing and also by anthropogenic-induced warming and aerosol forcing.

Distinct atmosphere-ocean coupling processes on the onset phase of Indian summer monsoon during 2017 and 2018 as revealed through SCATSAT-1 and its comparison with CFSv2

ABSTRACT Distinct atmosphere-ocean coupled processes determine the inter-annual variability in the onset processes of Indian Summer Monsoon. In this work, we have analysed the distinct characteristics of onset process during 2017 (MOK17) and 2018 (MOK18) using SCATSAT-1 observations. Two years of dedicated SCATSAT-1 analysed winds and other flux datasets are used to understand distinct-coupled processes and further compared with coupled model forecasts from National Centres for Environmental Prediction (NCEP) Climate Forecast System version 2 (CFSv2). Air-sea coupled mechanism during 2017 and 2018 suggests that there is a delayed response (about one pentad) of atmosphere-ocean coupling over North Indian Ocean on the monsoon onset and its propagation during 2018. It is found that the influence of cyclone Mekunu formed over Western Arabian Sea disturbed the onset vortex formed over Eastern Arabian Sea during MOK18. The presence of cyclone Mekunu results in a sudden spike of East-west Sea Surface Temperature gradient, Latent Heat Flux and wind stress over Arabian Sea during one pentad before monsoon onset over Kerala. This created an onset like situation in the next pentad, and later the conditions are not favoured for the further progress of the monsoon. It leads to a weak onset followed by a sluggish and halted northward progression of monsoon during 2018. In the absence of a cyclonic system during the onset phase of MOK17, conventional onset and its further progress took place during 2017. Further comparison of SCATSAT-1 and other analysed data sets with the CFSv2 model show that the CFSv2 model is able to capture the atmosphere-ocean coupled processes during the onset phase up to four pentads in advance during MOK17. However, due to the presence of Mekunu cyclone before the monsoon onset limited the forecast skill of CFSv2 only up to two pentads in advance during MOK18. We found that the presence of strong convective instability due to strong synoptic-scale system can influence the skill of coupled model forecast in the extended range. The new SCATSAT-1 observations provide high-quality observations that can be used to quantify the errors and identify common biases in the coupled models.

Impact of electrified and non-electrified clouds on the inter-seasonal characteristics of surface-based precipitation

A multi-sensor analysis of the characteristics of electrified and non-electrified clouds along with their impact on the surface-based raindrop size distribution (DSD) during the inter-seasonal phases of Indian summer monsoon over a heavy precipitation region of Western Ghat (WG) has been highlighted in the present paper. The analysis reveals that during the pre-monsoon (monsoon) months, raindrops of larger diameter dominate the rainfall evolving from the non-electrified (electrified) clouds compared to the rainfall evolving from the electrified (non-electrified) ones. The complex relationship of the convective rainfall with highly charged electrified clouds forces the smaller drops aloft and thereby allowing the larger drops to precipitate locally during the pre-monsoon season. While for the monsoon months, as most of the rainfall originates from the deep clouds, the chances of drops to break-up/evaporate is comparatively less for the precipitation evolving from electrified clouds with charged droplets with respect to the non-electrified ones. Hence, drops of larger diameter dominate the monsoon rainfall associated with lightning. Correspondingly, the paper also highlighted a case study of the changing morphology of the vertical structure of clouds and surface precipitation with the evolution of lightning during various stages of a typical rainfall event over the orographic region of WG.

Indian summer monsoon variability during the last millennium as recorded in stalagmite from Baratang Mahadev cave, Andaman Islands

This study presents a stable oxygen isotope record of Indian summer monsoon (ISM) variability using cave speleothem carbonate from Baratang Island (Andaman Islands) encompassing the last millennium (from 10th to 19th century CE). The studied interval encompasses two major climatic events; the Medieval Climate Anomaly (MCA) and the Little Ice Age (LIA) as well as the Current Warm Period (CWP). Our data suggest generally higher precipitation during the warm MCA when the ISM was relatively strong, and low precipitation during the cold LIA with a few exceptions when wet conditions prevailed. The Baratang cave record shows greater similarity with the records from the Sahiya and Klang caves, and opposite trends relative to those from the northeastern Himalaya owing to the dipolar nature of ISM precipitation. High-frequency sub-decadal to centennial scale pulses of weakened summer monsoons are observed during 16th to 19th century CE. These phases of weak ISM are correlated with severe droughts and famines in the Indian subcontinent owing to deficient monsoon rainfall, which had pronounced effect on South Asian societies. Spectral analysis suggests a strong periodicity of 190 yr (de Vries cycle) indicating strong influence of solar insolation.

Changes in the relationship between Indian Ocean dipole and Indian summer monsoon rainfall in early and recent multidecadal epochs during different phases of monsoon

AbstractIn this study, we explored the changes in the Indian Ocean Dipole‐Indian summer monsoon rainfall (IOD‐ISMR) relationship from early (1951–1980) to recent (1986–2015) multidecades during onset (June), peak (July–August) and withdrawal (September) phases of Indian summer monsoon. The analyses indicate that the IOD‐ISMR relationship is strengthening (weakening) during withdrawal (onset) phases over most of the Indian regions in the recent decades. During the peak phase, the relationship changes from out‐of‐phase (negative correlation) to in‐phase (positive correlation) in most of the Indian subcontinent. During positive IOD (pIOD) events, an increase in rainfall during all the phases is observed over the Indian region in the recent decades. Conversely, a general decrease in rainfall is observed over the Indian subcontinent during negative IOD (nIOD) events, except for the onset phase. The changes in sea surface temperature (SST), low level circulation and moisture transport over the equatorial Indian Ocean are linked to the changes in rainfall during both the positive and negative IOD events in the recent decades. However, most noticeable changes are observed during the peak and withdrawal phases. In the recent decades, during all the phases, a relatively strengthened low level jet (LLJ) with respect to the early decades is observed over the equatorial Indian Ocean and Arabian Sea associated with pIOD events. It causes a zone of moisture convergence over the northeast regions of India, which is conducive for above normal rainfall conditions in the monsoon trough zone and central Indian regions. In the case of nIOD events, the relatively weakened (strengthened) LLJ with respect to the early decades suppresses (enhances) the transport of moisture to the Indian region during the peak and withdrawal (onset) phases and cause reduced (enhanced) rainfall conditions. The observed results are more robust during the peak and withdrawal phases than that during the onset phase.

Changes in ENSO-monsoon relations from early to recent decades during onset, peak and withdrawal phases of Indian summer monsoon

The El Nino Southern Oscillation (ENSO) is an important coupled ocean–atmosphere phenomenon in the tropical Pacific and an important modulator of the spatio-temporal variability of Indian summer monsoon rainfall (ISMR). Here, we explore the impact of ENSO during onset (June), peak (July–August) and withdrawal (September) phases of ISMR for the period 1951–2015, by studying the changes in the ENSO-monsoon relationship from early decades (1951–1980) to recent decades (1986–2015). We observe noticeable changes in the ENSO-monsoon relationship from the early to recent decades during all the three phases. During El Nino events, rainfall over most of the Indian regions is significantly increased in recent decades during onset phase, but a significant decrease in rainfall is observed during peak and withdrawal phases. On the other hand, the rainfall during La Nina events is significantly decreased over the monsoon core zone of India during all the three phases. A significant increase (decrease) in sea surface temperature (SST) is observed over the central equatorial Pacific and Indian Ocean during El Nino (La Nina) events in recent decades. These changes differ from one phase to another and related to the observed rainfall patterns over the Indian region. Apart from these, the changes in the anomalies of low level circulation and Walker circulation over the Indo-Pacific domain are also linked to the changes in rainfall during the ENSO events, with most significant relationship during the onset phase.

How changing cloud water to rain conversion profile impacts on radiation and its linkage to a better Indian summer monsoon rainfall simulation

Effect of modifying cloud water to rain conversion factor above freezing level on radiation flux is studied. The linkage of cloud-radiation interaction with a better Indian summer monsoon (ISM) rainfall simulation has also been investigated. Two simulations were performed with Climate Forecast System version 2 (CFSv2), one with default revised simplified Arakawa-Schubert (RSAS) convection scheme and another with modified RSAS (RSAS-mod) in which the cloud water to precipitation conversion factor is revised. It is observed that both top of the atmosphere (TOA) and surface energy imbalances are improved in the RSAS-mod simulation. The major contribution seems to come from the enhanced reflected shortwave radiation at the TOA. In RSAS-mod, more shortwave radiation is getting reflected at the TOA and thus less shortwave is available to reach at the surface. It has happened as a consequence of enhanced planetary albedo in RSAS-mod. It is also observed that high cloud cover has increased in RSAS-mod and there is a decrease in low cloud cover. As a result of increased high cloud cover, outgoing longwave radiation has decreased significantly in RSAS-mod. It is also found from the multivariate empirical orthogonal function (MV-EOF) analysis that the composite of longwave cloud radiative forcing corresponding to phases 4 and 5 of boreal summer intraseasonal oscillation (BSISO), which signifies the active phase of ISM, is better simulated in RSAS-mod. This has helped to simulate a better seasonal rainfall.

Role of Intra-Seasonal Variability in the Indian Summer Monsoon on the Hydration and Dehydration of the Upper Troposphere

Seven years of high-resolution measurements of upper tropospheric humidity (UTH) from the Indian Geostationary satellite, Kalpana-1, are used to understand the hydration and dehydration processes during the active and break phases of the Indian summer monsoon (ISM). The active and break phases are identified using the TRMM-3B42 daily rainfall data over the Central Indian region. The most significant and new observation is that the upper troposphere is dry during the active and wet during the break phases of the ISM. Satellite measurements of humidity from Megha-Tropiques SAPHIR and water vapor mixing ratio from Aura microwave limb sounder also show dryness in the upper troposphere during the active and wetness during the break phases of ISM. The analysis illustrates that dehydration dominates during the active and hydration during the break phases. Cloud-aerosol lidar with orthogonal polarization data shows that cirrus (sub-categorized as sub-visible, thin, and thick) occurrence is more during the active phase as compared with the break phase. The dehydration mechanism during the active phase of ISM is attributed to the presence of cirrus. This study provides evidence that the upper troposphere shows dehydration during the active and hydration during the break phase of the ISM, thereby exhibiting intra-seasonal variability in the UTH.

Specific response of earlywood and latewood δ18O from the east and west of Mt. Qomolangma to the Indian summer monsoon

This study reports the earlywood and latewood δ18O time series from two hemlock sites located to the east (EQ) and west (WQ) of Mt. Qomolangma (Everest) in the Himalaya. The latewood δ18O series from both sites were highly consistent, whereas the earlywood δ18O values for the two sites show variations over the investigation period. Climate response analysis revealed that the dominant control on latewood δ18O values at both sites was the precipitation amounts of the middle/peak periods of upstream Indian Summer Monsoon (ISM). However, for EQ- and WQ-Earlywood, the main controls were precipitation amounts during the early and middle phases of the upstream ISM, respectively. The upstream amount effect could have accounted for earlywood and latewood δ18O variance. Combined with moisture transport models, we found that source water incorporated into latewood at both sites was derived mainly from the Bay of Bengal and Arabian Sea during middle/peak ISM precipitation. However, during the early ISM, the high ridges of Mt. Qomolangma may block most of the moisture that originates from the Bay of Bengal, which results in a stronger signal of early ISM being recorded in EQ-Earlywood δ18O. The influence of the ISM on WQ-Earlywood is delayed until the middle ISM.

Indian summer monsoon onset signatures on the tropical tropopause layer

Over the Indian region, changes in the tropopause parameters during pre‐monsoon to monsoon seasons have been reported. However, no study exists to date dealing with the Indian summer monsoon (ISM) onset signatures on the tropopause parameters. In the present study, the climatological structure of the tropical tropopause layer during the onset phase of ISM is delineated by using long‐term (2006–2017) radiosonde observations over Gadanki (13.5°N, 79.2°E). A prominent transition in the tropopause parameters from pre‐monsoon to monsoon is noticed and the transition is initiated from the day of ISM onset. Continuous decrease (increase) of tropopause altitude (temperature) is perceived after the ISM onset. The ozonesonde observations clearly show the strong enhancement in the ozone mixing ratio in the lower stratosphere (~16–20 km) after the ISM onset. This clearly demonstrates the instantaneous warming of the tropopause region after the ISM onset in addition to the latent heat release due to the precipitation. Transitions from pre‐monsoon to monsoon in the tropopause parameters are influenced strongly by onset of ISM which was attributed as seasonal changes earlier. These results provide strong evidence on the ISM onset signatures on the tropical tropopause parameters.

Added value of CORDEX‐SA experiments in simulating summer monsoon precipitation over India

Regional climate models (RCMs) serve as an important tool to perform high resolution climate simulations for a limited area. However, there remains a crucial issue regarding the efficacy of RCMs that whether they are able to produce added value (AV) in representing the regional climatic features compared to their coarse scale driving Global climate models (GCMs). The present study aims at assessing the AV of a set of RCM simulations performed under the Coordinated Regional Climate Downscaling Experiments‐South Asia (CORDEX‐SA) compared with their respective driving GCMs in representing the Indian summer monsoon (ISM) precipitation and its dynamical features. For this purpose, the performance of RCMs and GCMs is compared for the present day climate (1970–2005) against observations and reanalysis datasets in terms of various ISM features, that is, the spatial distribution of precipitation, the evolution of vertical shear of zonal wind and the onset phase of ISM in terms of delayed or early arrival of monsoon. The RCMs show a clear improvement upon their corresponding driving GCMs in simulating spatial features of precipitation distribution that are characteristically associated with ISM. Regionally, the RCMs also show skill in capturing the precipitation amount as a reduction in bias is found compared with their driving GCMs. There is a significant improvement in the simulation of onset dates of ISM by only some of the experiments particularly, RegCM4 driven with IPSL‐CM5A‐LR. The study concludes that the present set of CORDEX‐SA RCM simulations do indeed add value to their driving GCMs for a number of features associated with the ISM precipitation but this value varies with region, driving GCM and the particular feature of ISM under focus.

Genesis and track prediction of pre-monsoon cyclonic storms over North Indian Ocean in a multi-model ensemble framework

An attempt has been made in this study to evaluate the performance of a multi-model ensemble prediction system (MMEPS) in the extended range prediction of genesis and track of cyclonic storms (CS) over North Indian Ocean (NIO) during the onset phase of Indian summer monsoon. The MMEPS comprises of National Centres for Environmental Prediction Climate Forecast System version 2 and its atmospheric component, Global Forecast System version 2, at two different resolutions. In this study, we analyse the performance of this MMEPS in the prediction of six CS cases formed around the onset phase of the Indian summer monsoon over NIO. Along with this, we evaluate the usefulness of the genesis potential parameter used by India Meteorological Department (IMD) for the real-time cyclogenesis prediction. ERA-Interim re-analysis data sets are used to compare MME predictions from two initial conditions (IC) close to the genesis date of each storm. Results show that genesis forecasts from nearest available IC is capturing the vorticity and associated features of the storm better than far-IC. A modified version of vortex tracking scheme developed by Geophysical Fluid Dynamics Laboratory is used to obtain the mean track positions from MME outputs and compare with IMD-best tracks. Track verification is done by calculating average direct position error, cross-track error and along-track error against corresponding IMD-best tracks. It is found that track predictions from both near and far ICs have lower average errors initially with near-IC having lesser errors as compared to far-IC. Along-track error for pre-genesis track prediction from far-IC implies that the predicted tracks remarkably lag behind observed tracks for most of the cases. These errors could be contributed from the inability of the models in realistically capturing the region of evolution and intensification of both thermodynamic and dynamic parameters with increasing lead time.

Indian summer monsoon variability and vegetation changes in the core monsoon zone, India, during the Holocene: A multiproxy study

We present the results of sediment texture, δ13C values, TOC, TN, TOC/TN, and magnetic susceptibility (χlf) of a 1.54-m deep sediment trench recovered from the core monsoon zone (CMZ) of central India, to understand the paleovegetational history and Indian summer monsoon (ISM) variability during the Holocene. The lower δ13C values, TOC/TN ratio, and magnetic susceptibility (χlf) from ~11.4 to 9.5 ka BP suggest enhanced ISM intensity, which is well correlated with other available ISM records from both terrestrial as well as marine archives. A gradual stepwise expansion of C4 plants during ~8.1 and 6.3 ka BP, ~6.3 to 4.7 ka BP, and ~3.0 to 2.0 ka BP suggests a gradual weakening of ISM. The highest δ13C values (–18.7‰) recorded at ~2.0 ka BP indicate the dominance of C4 plants suggesting the weakest phase of ISM in the study area. The expansion of C3 plants from ~2.0 to 1.6 ka BP indicates a sudden increase in ISM intensity. Subsequently, three stages of enhanced ISM have been recorded between ~1.6 and 0.93 ka BP, ~0.76 and 0.42 ka BP, and ~0.28 ka BP to present.

Performance of Regional Climate Model in Simulating Monsoon Onset Over Indian Subcontinent

The performance of various Convective Parameterization Schemes (CPSs) of Regional Climate Model version 4.3 (RegCM-4.3) for simulation of onset phase of Indian summer monsoon (ISM) over Kerala was studied for the period of 2001–2010. The onset date and its associated spatial variation were simulated using RegCM-4.3 four core CPS, namely Kuo, Tiedtke, Emanuel and Grell; and with two mixed convection schemes Mix98 (Emanuel over land and Grell over ocean) and Mix99 (Grell over land and Emanuel over ocean) on the basis of criteria given by the India Meteorological Department (IMD) (Pai and Rajeevan in Indian summer monsoon onset: variability and prediction. National Climate Centre, India Meteorological Department, 2007). It has been found that out of six CPS, two schemes, namely Tiedtke and Mix99 simulated the onset date properly. The onset phase is characterized with several transition phases of atmosphere. Therefore, to study the thermal response or the effect of different sea surface temperature (SST), namely ERA interim (ERSST) and weekly optimal interpolation (OI_WK SST) on Indian summer monsoon, the role of two different types of SST has been used to investigate the simulated onset date. In addition, spatial atmospheric circulation pattern during onset phase were analyzed using reanalyze dataset of ERA Interim (EIN15) and National Oceanic and Atmospheric Administration (NOAA), respectively, for wind and outgoing long-wave radiation (OLR) pattern. Among the six convective schemes of RegCM-4.3 model, Tiedtke is in good agreement with actual onset dates and OI_WK SST forcing is better for simulating onset of ISM over Kerala.

Impact of intra-seasonal oscillations of Indian summer monsoon on biogeochemical constituents of North Indian Ocean

The intra-seasonal perturbations in the atmospheric weather are closely related to the variability in the ocean circulation. NASA Ocean Biogeochemical Model (NOBM) couples the oceanic general circulation and the radiative forcing. The NOBM model products of nitrate, total chlorophyll, and mixed layer depth (MLD) collected during the period from 1998 to 2007 as well as the sea surface temperature (SST), precipitation, outgoing long wave radiation (OLR), and wind are considered in this study to identify the influence of intra-seasonal oscillation (ISO) of Indian summer monsoon (ISM) on the biogeochemical constituents of Bay of Bengal (BOB) (6°–22° N; 80°–100° E) and Arabian Sea (AS) (3°–17° N; 55°–73.5° E) of North Indian Ocean (NIO). The active and break phases are the most significant components of ISO during ISM. The result of the study reveals that the upper ocean biology and chemistry significantly vary during the said phases of ISM. The nitrate, total chlorophyll, and MLD are observed to be strongly correlated with the ISO of ISM. The result shows that, during ISO of ISM, the concentration of nitrate and chlorophyll is strongly and positively correlated both in BOB and AS. However, the correlation is more in AS, endorsing that the Arabian Sea is more nutrient reach than Bay of Bengal. Nitrate and MLD, on the other hand, are strongly but negatively correlated in the said basins of North Indian Ocean (NIO). The forcing behind the variability of the biogeochemical constituents of BOB and AS during active and break phases of ISM is identified through the analyses of SST, precipitation, OLR, and wind.

Regional Climate Model Performance in Simulating Intra-seasonal and Interannual Variability of Indian Summer Monsoon

Establishment of Indian summer monsoon (ISM) rainfall passes through the different phases and is not uniformly distributed over the Indian subcontinent. This enhancement and reduction in daily rainfall anomaly over the Indian core monsoon region during peak monsoon season (i.e., July and August) are commonly termed as ‘active’ and ‘break’ phases of monsoon. The purpose of this study is to analyze REGional Climate Model (RegCM) results obtained using the most suitable convective parameterization scheme (CPS) to determine active/break phases of ISM. The model-simulated daily outgoing longwave radiation (OLR), mean sea level pressure (MSLP), and the wind at 850 hPa of spatial resolution of 0.5°× 0.5° are compared with NOAA, NCEP, and EIN15 data, respectively over the South-Asia Co-Ordinated Regional Climate Downscaling EXperiment (CORDEX) region. 25 years (1986–2010) composites of OLR, MSLP, and the wind at 850 hPa are considered from start to the dates of active/break phase and up to the end dates of active/break spell of monsoon. A negative/positive anomaly of OLR with active/break phase is found in simulations with CPSs Emanuel and Mix99 (Grell over land; Emanuel over ocean) over the core monsoon region as well as over Monsoon Convergence Zone (MCZ) of India. The appearance of monsoon trough during active phase over the core monsoon zone and its shifting towards the Himalayan foothills during break phase are also depicted well. Because of multi-cloud function over oceanic region and single cloud function over the land mass, the Mix99 CPSs perform well in simulating the synoptic features during the phases of monsoon.