Hamza Varikoden, Bhupendra Bahadur Singh, K. P. Sooraj, Manish K. Joshi, Preethi Bhaskar, Milind Mujumdar, M. Rajeevan
During 2015, the southwest monsoon (SWM) rainfall over the country remained deficient with seasonal rainfall of about 86% of the long period average (Table 1.1). Last year, the seasonal rainfall deficiency over the country as a whole was 12% (www.imd.gov.in). Thus, this is a fourth episode of two consecutive years, with deficient monsoon, similar to 1904-05, 1965-66 and 1986-87 (www.imd.gov.in).
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Summer monsoon rainfall over India depends on synoptic-scale phenomena like lows and depressions. India's summer monsoon season 2020 saw above-average rainfall. North Indian Ocean had 12 LPAs in summer 2020 in JJAS season. This monsoon season has the highest all-India rainfall since 1976 in August 2020. 50% of seasonal LPAs emerged in August 2020, but none intensified into a monsoon depression (MDs). This study explores the potential factors behind LPAs not intensifying/concentrating as MDs. Warming over the Northern Parts of the Arabian Sea (NPAS) boosted convection in August 2020, resulting …
More extreme Indian monsoon daily rainfall in El Niño summers
本研究利用1901-2020年观测数据发现，厄尔尼诺虽使印度夏季平均降雨减少，却显著增加季风区极端日降雨概率，尤其在中东部和西南沿海，其机制与对流浮力相关，并预示季节预报潜力。
Intraseasonal Oscillation of Land Surface Moisture and its role in the maintenance of land ITCZ during the active phases of the Indian Summer Monsoon
本研究利用ERA5和CFS自由试验分析印度夏季风活跃期土壤湿度的季节内振荡及其对陆地ITCZ和降雨的预调节与MSE反馈，指出模式需真实表征土壤湿度预调节。
Intraseasonal synchronization of extreme rainfalls between North India and the Sahel
本研究用气候网络方法揭示印度夏季风与西非季风系统间极端降水的季节内同步规律，明确其关联滞后时长及驱动机制，增进了对两大季风系统相互作用的理解。
Measurements of the small-, intermediate-, and large-ion concentrations and the atmospheric electric conductivity of both polarities have been made over the Arabian Sea on four cruises of ORV Sagarkanya during the Arabian Sea Monsoon Experiment (ARMEX)during the monsoon and pre-monsoon seasons of 2002 and 2003. Seasonally averaged values of the total as well as polar conductivity are much higher during the monsoon than pre-monsoon season. Surprisingly, however, the concentration of small ions are less and those of large and intermediate ions are more during the monsoon than pre-monsoon season.…
Understanding the soil water dynamics during excess and deficit rainfall conditions over the Core monsoon zone of India
本研究利用2000-2021年季风过剩与不足年份的土壤水分观测，分析印度核心季风区土壤水动态，发现地下土壤水分记忆时间约为地表两倍，蒸散发变化受断裂事件影响，强调地表-地下耦合观测的重要性。
The initiation of the Indian summer monsoon circulation during late May / early June arises through large-scale land-sea thermal contrast and setting up of negative pressure gradient between the Monsoon Trough over the Indo-Gangetic plains and the Mascarene High over the subtropical Indian Ocean. The meridional pressure gradient together with the Earth's rotation (Coriolis force) creates the summer monsoon cross-equatorial flow, while feedbacks between moisture-laden winds and latent heat release from precipitating systems maintain the monsoon circulation during the June-September (JJAS) rainy…
A comprehensive study of satellite-derived suspended sediment concentration (SSC) during pre- and post-monsoon has been conducted with full-month cycles of tidal responses to study the suspended sediment dynamics in the Gulf of Kachchh. Tidal data were interpreted in conjunction with the OCEANSAT-1 ocean color monitor (OCM)-derived SSC for pre- and post-monsoon. The analysis of the data shows that the Gulf is predominantly affected by the tidal changes. The average SSC during pre-monsoon were 30.8 mg/l (high tide) and 24.1 mg/l (low tide); and during post-monsoon 19.7 mg/l (high tide) and 21.8…
Four case studies of cyclonic vortices over the Indian peninsular region during northeast monsoon season are presented. It was observed that the propagation of vortices over the peninsular orography was controlled by the vortex Froude number, Frv = Vmax/(NH), where, Vmax is the maximum tangential velocity of winds in the vortex, H is the height of the orography, and N is the Brunt-Vaisala frequency of atmosphere along the orography. Strong vortices with Frv > 1 overcame the orographic barrier and crossed the peninsula. While, those with Frv < 1 were blocked by the orography. The blocked vortic…
The sub-seasonal and synoptic-scale variability of the Indian summer monsoon rainfall are controlled primarily by monsoon intra-seasonal oscillations (MISO) and low pressure systems (LPS), respectively. The positive and negative phases of MISO lead to alternate epochs of above-normal (active) and below-normal (break) spells of rainfall. LPSs are embedded within the different phases of MISO and are known to produce heavy precipitation events over central India. Whether the interaction with the MISO phases modulates the precipitation response of LPSs, and thereby the characteristics of extreme r…
The Indian summer monsoon rainfall (ISMR) has a decisive influence on India's agricultural output and economy. Extreme deviations from the normal seasonal amount of rainfall can cause severe droughts or floods, affecting Indian food production and security. Despite the development of sophisticated statistical and dynamical climate models, a long-term and reliable prediction of the ISMR has remained a challenging problem. Towards achieving this goal, here we construct a series of dynamical and physical climate networks based on the global near surface air temperature field. We uncover that some…
The Bay of Bengal (BoB) is a high recipient of freshwater flux from rivers and precipitation, making the region strongly stratified. The strong stratification results in a thick barrier layer formation, which inhibits vertical mixing making this region a low-productive zone. In the present study, we attempt to model the pH of the BoB region and understand the role of different governing factors such as sea-surface temperature (SST), sea-surface salinity (SSS), dissolved inorganic carbon (DIC), and total alkalinity (TALK) on the seasonality of sea-surface pH. We run a set of sensitivity experim…
Evaluation of High-Resolution Gridded Precipitation Datasets Against a Dense Rain Gauge Network During the Indian Summer Monsoon
该研究针对印度夏季风期间，基于卡纳塔克邦密集雨量计网络评估六种高分辨率网格化降水数据集，运用复杂网络理论工具，分析各数据集表现，发现GSMaP ISRO最佳，为改进降雨估计提供依据。
The correlation between increased Sahel rainfall and reduced Saharan surface pressure is well established in observations and global climate models, and has been used to imply that increased Sahel rainfall is caused by a stronger shallow meridional circulation (SMC) over the Sahara. This study uses two atmospheric reanalyses to examine interannual variability of Sahel rainfall and the Saharan SMC, which consists of northward near-surface flow across the Sahel into the Sahara and southward flow near 700 hPa out of the Sahara. During wet Sahel years, the Saharan SMC shifts poleward, producing a …
We study the role of galactic cosmic ray (GCR) variability in influencing the rainfall variability in Indian Summer Monsoon Rainfall (ISMR) season. We find that on an average during 'drought' (low ISMR) periods in India, GCR flux is decreasing, and during 'flood' (high ISMR) periods, GCR flux is increasing. The results of our analysis suggest for a possibility that the decreasing GCR flux during the summer monsoon season in India may suppress the rainfall. On the other hand, increasing GCR flux may enhance the rainfall. We suspect that in addition to real environmental conditions, significant …
MAUSAM: An Observations-focused assessment of Global AI Weather Prediction Models During the South Asian Monsoon
本文提出MAUSAM评估框架，利用地面站、雨量计和卫星观测检验七个AI天气模型在南亚季风期的表现，发现其技巧显著但精细尺度误差仍存，且再分析基准会高估性能。
Sub-seasonal Modulation and Predictability of Indian monsoon hourly Rainfall Extremes
研究通过识别小时降雨极值与地表温度、季风内季节振荡相位及可降水汽的三元聚类，建立中短期可预测性基础，开发算法追踪风暴系统，为深度学习模型提供物理指导以提前预测降雨极值集群。
GraphCast Skill and Systematic Biases in Indian Summer Monsoon Forecasts: Evaluation Against ERA5 and IMERG
该研究评估GraphCast对印度夏季风预测的保真度，将其与ERA5再分析和IMERG观测对比，分析不同提前期性能，发现GraphCast在短提前期能再现季风降雨模式，但存在湿偏差、降雨方差抑制等问题，为下一代AI天气模型提供关键诊断。
Towards better representation of Indian summer monsoon rainfall in CMIP6 models: Evaluation of MISO and MJO simulation
本研究评估了CMIP6模式对印度夏季风MISO和MJO的模拟能力，发现TaiESM1和IITM-ESM因更好地刻画对流和总云量而表现更优，为改进ISM气候预测提供了方向。
Prediction and Predictability of the Wet-Season Rainfall over Southeast India
研究发现印度东南部泰米尔邦湿季降雨受南海气温异常影响，长期预测能力源于热带印度洋与赤道大西洋的 SST 与降雨相互作用，为应对降雨变化提供了数据驱动的预测方法。
In this paper, the complexities in the relationship between rainfall and sea surface temperature (SST) anomalies during the winter monsoon (November-January) over India were evaluated statistically using scatter plot matrices and autocorrelation functions.Linear as well as polynomial trend equations were obtained and it was observed that the coefficient of determination for the linear trend was very low and it remained low even when polynomial trend of degree six was used. An exponential regression equation and an artificial neural network with extensive variable selection were generated to fo…
Emerging trend in the east-west Dipole Pattern in Indian Summer Monsoon Rainfall and the associated impact on Regional Dynamics
研究发现印度夏季降雨出现东-西偶极子模式变化，西北部降雨增加与阿拉伯海海表温度升高及风场变化有关，对区域气候动态产生影响。
Wavelet analysis of possible association between sunspot number and rainfall over Kerala, India: A case study
本文利用交叉小波变换分析了印度喀拉拉邦122年的太阳黑子数与降雨数据，发现不同太阳活动阶段及奇偶周期对极端季节性降水具有显著影响，揭示了两者间的物理联系。
Default values for many model parameters in Numerical Weather Prediction models are typically adopted based on theoretical or experimental investigations by scheme designers. Short-range forecasts are substantially affected by the specification of parameters in the Weather Research and Forecasting (WRF) model. The presence of a multitude of parameters and several output variables in the WRF model renders appropriate parameter value identification quite challenging. The objective of the current study is to reduce the uncertainty in the model outcomes through the recognition of parameters that s…
Using the Morlet continuous wavelet transform on data over the period 1871-1990, it is found that the global wavelet cross spectra between two solar activity indices and seven major Indian monsoon rainfall time series show significant power around the period of the 11 year solar cycle, passing the $χ^2$ test of significance proposed by Torrence and Compo (1998) at levels exceeding 95% in 10 out of the 14 cases studied. Furthermore two distinct epochs are found in the computed cross-spectrum, the transition between them occurring around the decade 1915-1925, beyond which solar activity paramete…
Spatio-temporal relationships between rainfall and convective clouds during Indian Monsoon through a discrete lens
本研究基于马尔可夫随机场模型的离散时空表示方法，分析2004-2010年印度季风期降雨与OLR的时空关系，发现少量模式可覆盖超90%日期的情况，揭示了二者的关联及逐日变化规律，为季风过程的简化描述提供工具。
We analyse Indian summer monsoon (ISM) seasonal reforecasts by CFSv2 model, initiated from January (4-month lead time, L4) through May (0-month lead time, L0) initial conditions (ICs), to examine the cause for highest all-India ISM rainfall (ISMR) forecast skill with February (L3) ICs. The reported highest L3 skill is based on correlation between observed and predicted interannual variation (IAV) of ISMR. Other scores such as mean error, bias, RMSE, mean, standard deviation and coefficient of variation, indicate higher or comparable skill for April(L1)/May(L0) ICs. Though theory suggests that …
Skilful prediction of the seasonal Indian summer monsoon (ISM) rainfall (ISMR) at least one season in advance has great socio-economic value. It represents a lifeline for about a sixth of the world's population. The ISMR prediction remained a challenging problem with the sub-critical skills of the dynamical models attributable to limited understanding of the interaction among clouds, convection, and circulation. The variability of cloud hydrometeors (cloud ice and cloud water) in different time scales (3-7 days, 10-20 days and 30-60 days bands) are examined from re-analysis data during Indian …
Solar activity and extreme rainfall over Kerala, India
本文研究了太阳活动指数与印度喀拉拉邦极端降雨的关系，发现两者在冬季相关性更强，且降雨盈亏年份多出现在太阳极大或极小期附近，为极端降雨的可预测性提供了物理假设。
The identification of regions of similar climatological behavior can be utilized for the discovery of spatial relationships over long-range scales, including teleconnections. In this regard, the global picture of the interdependence patterns of extreme rainfall events (EREs) still needs to be further explored. To this end, we propose a top-down complex-network-based clustering workflow, with the combination of consensus clustering and mutual correspondences. Consensus clustering provides a reliable community structure under each dataset, while mutual correspondences build a matching relationsh…
The role of Solar Activity in shaping Precipitation Extremes: A Regional Exploration in Kerala, India
本研究探讨了印度喀拉拉邦极端降水对太阳活动的响应，分析了1965-2021年三个太阳指数与降雨量的关系，发现太阳活动高发期冬季和季风期降水相关性显著，为预测极端降雨提供了物理依据。
Downscaling is necessary to generate high-resolution observation data to validate the climate model forecast or monitor rainfall at the micro-regional level operationally. Dynamical and statistical downscaling models are often used to get information at high-resolution gridded data over larger domains. As rainfall variability is dependent on the complex Spatio-temporal process leading to non-linear or chaotic Spatio-temporal variations, no single downscaling method can be considered efficient enough. In data with complex topographies, quasi-periodicities, and non-linearities, deep Learning (DL…
This study presents the first systematic comparison of the (thermo-)dynamics associated with all major tropical wave types causing rainfall modulation over northern tropical Africa: Madden Julian Oscillation (MJO), Equatorial Rossby waves (ERs), mixed Rossby-gravity waves (MRGs), Kelvin waves, tropical disturbances (TDs, including African Easterly Waves), and eastward inertio-gravity waves (EIGs). Reanalysis and radiosonde data were analyzed for the period 1981--2013 based on space-time filtering of outgoing longwave radiation. The identified circulation patterns are largely consistent with th…
Oceanic influence on Large-Scale Atmospheric Convection during co-occurring La Nina and IOD events
本研究针对2022年拉尼娜与负IOD共存时的ISMR异常格局，揭示了海洋次表层动力学通过开尔文波、罗斯贝波调控风辐合与海温，进而影响热带大尺度大气对流的机制，为季风变率预测提供了新视角。
In this paper we assess the snow cover and its dynamics for the western river basins of the Indus River system and their subbasins located in Afghanistan, China, India and Pakistan for the period 2001-2012. First, we validate the Moderate Resolution Imaging Spectroradiometer (MODIS) daily snow products from Terra and Aqua against the Landsat Thematic Mapper/Enhanced Thematic Mapper plus data set, and then improve them for clouds by applying a validated non spectral cloud removal technique. The improved snow product has been analysed on a seasonal and annual basis against different topographic …
Low-latitude rainfall variability on the daily to intraseasonal timescale is often related to tropical waves, including convectively coupled equatorial waves, the Madden-Julian Oscillation (MJO), and tropical disturbances. Despite the importance of rainfall variability for vulnerable societies in tropical Africa, the relative influence of tropical waves for this region is largely unknown. This article presents the first systematic comparison of the impact of six wave types on precipitation over northern tropical Africa during the transition and full monsoon seasons, using two satellite product…
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