This study examines the response of the tropical atmospheric and oceanic circulation to increasing greenhouse gases using a coordinated set of twenty-first-century climate model experiments performed for the Intergovernmental Panel on Climate Change (IPCC) Fourth Assessment Report (AR4). The strength of the atmospheric overturning circulation decreases as the climate warms in all IPCC AR4 models, in a manner consistent with the thermodynamic scaling arguments of Held and Soden. The weakening occurs preferentially in the zonally asymmetric (i.e., Walker) rather than zonal-mean (i.e., Hadley) component of the tropical circulation and is shown to induce substantial changes to the thermal structure and circulation of the tropical oceans. Evidence suggests that the overall circulation weakens by decreasing the frequency of strong updrafts and increasing the frequency of weak updrafts, although the robustness of this behavior across all models cannot be confirmed because of the lack of data. As the cli...

Global Warming and the Weakening of the Tropical Circulation

Using machine learning models, remote sensing, and GIS to investigate the effects of changing climates and land uses on flood probability

Commercial success of big data has led to speculation that big-data-like reasoning could partly replace theory-based approaches in science. Big data typically has been applied to ‘small problems’, which are well-structured cases characterized by repeated evaluation of predictions. Here, we show that in climate research, intermediate categories exist between classical domain science and big data, and that big-data elements have also been applied without the possibility of repeated evaluation. Big-data elements can be useful for climate research beyond small problems if combined with more traditional approaches based on domain-specific knowledge. The biggest potential for big-data elements, we argue, lies in socioeconomic climate research. Big data is increasingly popular in many research domains. This Perspective discusses where elements of big data approaches have been employed in climate research and where combining big data with theory-driven research can be most fruitful.

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Applying big data beyond small problems in climate research

Grasslands are an important component of terrestrial ecosystems that play a crucial role in the carbon cycle and climate change. In this study, we collected aboveground biomass (AGB) data from 223 grassland quadrats distributed across the Loess Plateau from 2011 to 2013 and predicted the spatial distribution of the grassland AGB at a 100-m resolution from both meteorological station and remote sensing data (TM and MODIS) using a Random Forest (RF) algorithm. The results showed that the predicted grassland AGB on the Loess Plateau decreased from east to west. Vegetation indexes were positively correlated with grassland AGB, and the normalized difference vegetation index (NDVI) acquired from TM data was the most important predictive factor. Tussock and shrub tussock had the highest AGB, and desert steppe had the lowest. Rainfall higher than 400 m might have benefitted the grassland AGB. Compared with those obtained for the bagging, mboost and the support vector machine (SVM) models, higher values for the mean Pearson coefficient (R) and the symmetric index of agreement (λ) were obtained for the RF model, indicating that this RF model could reasonably estimate the grassland AGB (65.01%) on the Loess Plateau.

/pdf/prediction-of-aboveground-grassland-biomass-on-the-loess-4r4ekquuhs.pdf

Prediction of aboveground grassland biomass on the Loess Plateau, China, using a random forest algorithm

Detection of changes and trends in climatic variables in Bangladesh during 1988-2017.

Can Nor'wester events initiate stratospheric moistening?

In this study, it has been attempted to understand the role of various factors such as orography, moisture availability, aerosol nucleation, and atmospheric instability behind the spatio-temporal distribution of lightning properties over the Equatorial Central African region which experiences the most frequent lightning activity globally. Detailed statistical analysis using high-resolution satellite observations reveals very high lightning frequencies along the Virunga Mountain ranges during the summer season owing to its orographic advantage while the maximum flash radiances are observed over the relatively low-lying Congo River Basin during the month of June because of high moisture, instability, and aerosol availability in that region.

Climatology of lightning activities across the Equatorial African region

Rain attenuation is an important aspect of signal propagation mainly above 10 GHz frequency. It has also been found that the rain rate and attenuation profiles along the vertical and slant propagation path, especially at a higher rain rates and at tropical location. In this study, a simple approach is taken to study rain attenuation at various frequencies from propagation data and ground based radar measurements at Kolkata, INDIA. The ITU-R Model and the SAM Model has been utilized to provide an estimate of the slant rain rate and total attenuation from the vertical rain rate profiles.

Rain attenuation over earth space path from radar and propagation measurements at tropical location

/pdf/lightning-prediction-using-electric-field-measurements-3r9glhgk.pdf

Lightning Prediction Using Electric Field Measurements Associated with Convective Events at a Tropical Location

Nowcasting of rain amount is extremely essential in various fields of life. In this paper, we have shown that monitoring of brightness temperature at 31.4 GHz, the frequency having strong absorption due to liquid water, can give an estimate of rain accumulation with a prediction efficiency of ∼ 80 % and a lead time of 75 minutes. It has also been observed that atmospheric electric field also shows definite changes before rain the magnitude of which can be related with the rainfall amount.

http://ieeexplore.ieee.org/iel7/7589831/7601069/07601354.pdf

Rohit Chakraborty

Papers

Can Nor'wester events initiate stratospheric moistening?

Climatology of lightning activities across the Equatorial African region

Rain attenuation over earth space path from radar and propagation measurements at tropical location

Lightning Prediction Using Electric Field Measurements Associated with Convective Events at a Tropical Location

Prediction of convective rainfall using multi-technique observations