scholarly journals Simulation of Daily Rainfall from Concurrent Meteorological Parameters over Core Monsoon Region of India: A Novel Approach

2018 ◽  
Vol 2018 ◽  
pp. 1-18
Author(s):  
Utpal Misra ◽  
Atri Deshamukhya ◽  
Sanjay Sharma ◽  
Srimanta Pal
Keyword(s):  
Meteorological Parameters ◽  
Good Accuracy ◽  
Daily Rainfall ◽  
Meridional Wind ◽  
Specific Humidity ◽  
Monsoon Region ◽  
Intraseasonal Variation ◽  
Coupled Models ◽  
Novel Approach ◽  
Mlp Model

In the present work, daily rainfall is simulated over the core monsoon region of India by using a feedforward multilayer perceptron (MLP) model. Daily rainfall is found to be optimally dependent on four concurrent meteorological parameters, namely, geopotential height, specific humidity, zonal, and meridional wind at 1000 mb, 925 mb, 850 mb, and 700 mb pressure levels during 00, 06, 12, and 18 Greenwich Mean Time (GMT). The architecture of the optimized feedforward MLP model consists of 64 nodes in the input layer, 10 nodes in the hidden layer, and 1 node in the output layer. The results from the model are compared with the 3B42 (version 7) rainfall product. In terms of root mean square error (rmse) and correlation coefficient (cc), the model is performing better compared to the satellite-derived 3B42 rainfall product, whereas in terms of bias, the performance of the 3B42 product is better compared to the model. The weight matrices of the feedforward MLP model are estimated at a particular location (22.5°N, 82.5°E). These weight matrices are able to simulate daily rainfall at neighbourhood locations also with reasonably good accuracy with cc in the range of 0.41 to 0.55. The performance of the model improves in case of an aerial average of daily rainfall with significantly enhanced cc (0.72). The model is able to capture monthly and intraseasonal variation of rainfall with reasonably good accuracy, with cc of 0.88 and 0.68, respectively. The simulation model has a limitation that it is not able to simulate extreme high rainfall events (>60 mm/day). Overall, the developed model is performing reasonably well. This approach has a potential to be used as a rain parameterization scheme in the dynamical atmospheric and coupled models to simulate daily rainfall. Nevertheless, the present approach can also be used for multistep prediction of rainfall.

scholarly journals Investigating the Causes of Increased Twentieth-Century Fall Precipitation over the Southeastern United States

2018 ◽  
Vol 32 (2) ◽  
pp. 575-590 ◽  
Author(s):  
Daniel A. Bishop ◽  
A. Park Williams ◽  
Richard Seager ◽  
Arlene M. Fiore ◽  
Benjamin I. Cook ◽  
...  
Keyword(s):  
United States ◽  
Twentieth Century ◽  
Gulf Of Mexico ◽  
Specific Humidity ◽  
Precipitation Trend ◽  
Eastern United States ◽  
Atmospheric Models ◽  
Coupled Models ◽  
Fully Coupled ◽  
Precipitation Trends

Abstract Much of the eastern United States experienced increased precipitation over the twentieth century. Characterizing these trends and their causes is critical for assessing future hydroclimate risks. Here, U.S. precipitation trends are analyzed for 1895–2016, revealing that fall precipitation in the southeastern region north of the Gulf of Mexico (SE-Gulf) increased by nearly 40%, primarily increasing after the mid-1900s. Because fall is the climatological dry season in the SE-Gulf and precipitation in other seasons changed insignificantly, the seasonal precipitation cycle diminished substantially. The increase in SE-Gulf fall precipitation was caused by increased southerly moisture transport from the Gulf of Mexico, which was almost entirely driven by stronger winds associated with enhanced anticyclonic circulation west of the North Atlantic subtropical high (NASH) and not by increases in specific humidity. Atmospheric models forced by observed SSTs and fully coupled models forced by historical anthropogenic forcing do not robustly simulate twentieth-century fall wetting in the SE-Gulf. SST-forced atmospheric models do simulate an intensified anticyclonic low-level circulation around the NASH, but the modeled intensification occurred farther west than observed. CMIP5 analyses suggest an increased likelihood of positive SE-Gulf fall precipitation trends given historical and future GHG forcing. Nevertheless, individual model simulations (both SST forced and fully coupled) only very rarely produce the observed magnitude of the SE-Gulf fall precipitation trend. Further research into model representation of the western ridge of the fall NASH is needed, which will help us to better predict whether twentieth-century increases in SE-Gulf fall precipitation will persist into the future.

scholarly journals A novel approach for the extraction of cloud motion vectors using airglow imager measurements

2015 ◽  
Vol 8 (9) ◽  
pp. 3893-3901 ◽  
Author(s):  
S. Satheesh Kumar ◽  
T. Narayana Rao ◽  
A. Taori
Keyword(s):  
Meridional Wind ◽  
Noise Removal ◽  
Search Window ◽  
Motion Vectors ◽  
Good Correspondence ◽  
Cloud Motion ◽  
Cloud Height ◽  
Novel Approach ◽  
Wind Velocities ◽  
Cloud Tracking

Abstract. The paper explores the possibility of implementing an advanced photogrammetric technique, generally employed for satellite measurements, on airglow imager, a ground-based remote sensing instrument primarily used for upper atmospheric studies, measurements of clouds for the extraction of cloud motion vectors (CMVs). The major steps involved in the algorithm remain the same, including image processing for better visualization of target elements and noise removal, identification of target cloud, setting a proper search window for target cloud tracking, estimation of cloud height, and employing 2-D cross-correlation to estimate the CMVs. Nevertheless, the implementation strategy at each step differs from that of satellite, mainly to suit airglow imager measurements. For instance, climatology of horizontal winds at the measured site has been used to fix the search window for target cloud tracking. The cloud height is estimated very accurately, as required by the algorithm, using simultaneous collocated lidar measurements. High-resolution, both in space and time (4 min), cloud imageries are employed to minimize the errors in retrieved CMVs. The derived winds are evaluated against MST radar-derived winds by considering it as a reference. A very good correspondence is seen between these two wind measurements, both showing similar wind variation. The agreement is also found to be good in both the zonal and meridional wind velocities with RMSEs < 2.4 m s−1. Finally, the strengths and limitations of the algorithm are discussed, with possible solutions, wherever required.

scholarly journals Associations between seasonal influenza and meteorological parameters in Costa Rica, Honduras and Nicaragua

2015 ◽  
Vol 10 (2) ◽  
Author(s):  
Radina P. Soebiyanto ◽  
Wilfrido A. Clara ◽  
Jorge Jara ◽  
Angel Balmaseda ◽  
Jenny Lara ◽  
...  
Keyword(s):  
Costa Rica ◽  
Central America ◽  
Seasonal Influenza ◽  
Meteorological Parameters ◽  
Correlation Coefficients ◽  
Tropical Rainfall Measuring Mission ◽  
Specific Humidity ◽  
Considerable Proportion ◽  
Influenza Activity ◽  
Land Data Assimilation System

Seasonal influenza affects a considerable proportion of the global population each year. We assessed the association between subnational influenza activity and temperature, specific humidity and rainfall in three Central America countries, <em>i.e.</em> Costa Rica, Honduras and Nicaragua. Using virologic data from each country’s national influenza centre, rainfall from the Tropical Rainfall Measuring Mission and air temperature and specific humidity data from the Global Land Data Assimilation System, we applied logistic regression methods for each of the five sub-national locations studied. Influenza activity was represented by the weekly proportion of respiratory specimens that tested positive for influenza. The models were adjusted for the potentially confounding co-circulating respiratory viruses, seasonality and previous weeks’ influenza activity. We found that influenza activity was proportionally associated (P&lt;0.05) with specific humidity in all locations [odds ratio (OR) 1.21-1.56 per g/kg], while associations with temperature (OR 0.69-0.81 per °C) and rainfall (OR 1.01-1.06 per mm/day) were location-dependent. Among the meteorological parameters, specific humidity had the highest contribution (~3-15%) to the model in all but one location. As model validation, we estimated influenza activity for periods, in which the data was not used in training the models. The correlation coefficients between the estimates and the observed were ≤0.1 in 2 locations and between 0.6-0.86 in three others. In conclusion, our study revealed a proportional association between influenza activity and specific humidity in selected areas from the three Central America countries.

Minimum Inter-Event Times for Rainfall in the Eastern Monsoon Region of China

2019 ◽  
Vol 62 (1) ◽  
pp. 9-18
Author(s):  
Wenting Wang ◽  
Wenting Wang ◽  
Shuiqing Yin ◽  
Yun Xie ◽  
Mark A. Nearing ◽  
...  
Keyword(s):  
Daily Rainfall ◽  
Precipitation Data ◽  
Monsoon Region ◽  
Average Value ◽  
Event Time ◽  
Hourly Data ◽  
Average Precipitation ◽  
Average Rainfall ◽  
Exponential Method ◽  
Event Times

Abstract.Minimum inter-event time (MIT) is an index used to delineate independent storms from sub-daily rainfall records. An individual storm is defined as a period of rainfall with preceding and succeeding dry periods less than MIT. The exponential method was used to determine an appropriate MITexp for the eastern monsoon region of China based on observed 1-min resolution rainfall data from 18 stations. Results showed that dry periods between storms greater than MITexp followed an exponential distribution. MITexp values varied from 7.6 h to 16.6 h using 1-min precipitation data, which were statistically not different from values using hourly data at p = 0.05. At least ten years of records were necessary to obtain a stable MIT. Values of storm properties are sensitive to the change in MIT values, especially when MIT values are small. Average precipitation depths across all stations were 45% greater, durations were 84% longer, maximum 30-min intensities were 27% greater, and average rainfall intensities were 20% less when using an MIT of 10 h, the average value of MITexp over 18 stations, compared to 2 h. This indicates that more attention should be paid to the use of the MIT index as it relates to storm properties. Keywords: China, Exponential method, Minimum inter-event time, Storm, Storm property.

scholarly journals Observational Evidence of the Transition from Shallow to Deep Convection in the Western Caribbean Trade Winds

Atmosphere ◽  
2019 ◽  
Vol 10 (11) ◽  
pp. 700 ◽  
Author(s):  
Yanet Díaz-Esteban ◽  
Graciela B. Raga
Keyword(s):  
Deep Convection ◽  
Meridional Wind ◽  
Specific Humidity ◽  
Wind Component ◽  
Regime Transition ◽  
Shallow Convection ◽  
Trade Winds ◽  
Convection Regime ◽  
Shallow Cumulus ◽  
Short Period

The present study aims to determine the factors influencing the transition from shallow to deep convection in the trade winds region using an observational approach, with emphasis in the Yucatan Peninsula in eastern Mexico. The methodology is based on a discrimination of two regimes of convection: a shallow cumulus regime, usually with little or no precipitation associated, and an afternoon deep convection regime, with large amounts of precipitation, preceded by a short period of shallow convection. Then, composites of meteorological fields at surface and several vertical levels, for each of the two convection regimes, are compared to infer which meteorological factors are involved in the development of deep convection in this region. Also, the relationship between meteorological variables and selected regime-transition parameters is evaluated only for deep convection regime days. Results indicate the importance of dynamic factors, such as the meridional wind component, in the transition from shallow to deep convection. As expected, thermodynamic variables, such as the low-level specific humidity in the shallow cumulus layer, also contribute to the regime transition. The presence of a southerly component of wind at low- to mid-levels during the early morning in deep convection days provides the shallow cumulus with a more favorable environment so that transition can occur, since abundant moisture from the Caribbean is supplied through this prevailing southern wind. The results can be relevant for reducing uncertainties regarding some important parameters in global and regional models, which could lead to improved simulations of the transition from shallow to deep convection and precipitation.

scholarly journals A novel approach for the extraction of cloud motion vectors using airglow imager measurements

2015 ◽  
Vol 8 (3) ◽  
pp. 2657-2682
Author(s):  
S. Satheesh Kumar ◽  
T. Narayana Rao ◽  
A. Taori
Keyword(s):  
Meridional Wind ◽  
Noise Removal ◽  
Search Window ◽  
Motion Vectors ◽  
Good Correspondence ◽  
Cloud Motion ◽  
Cloud Height ◽  
Novel Approach ◽  
Wind Velocities ◽  
Cloud Tracking

Abstract. The paper explores the possibility of implementing an advanced photogrammetric technique, generally employed for satellite measurements, on airglow imager, a ground-based remote sensing instrument primarily used for upper atmospheric studies, measurements of clouds for the extraction of cloud motion vectors (CMVs). The major steps involved in the algorithm remain the same, including image processing for better visualization of target elements and noise removal, identification of target cloud, setting a proper search window for target cloud tracking, estimation of cloud height, and employing 2-D cross-correlation to estimate the CMVs. Nevertheless, the implementation strategy at each step differs from that of satellite, mainly to suit airglow imager measurements. For instance, climatology of horizontal winds at the measured site has been used to fix the search window for target cloud tracking. The cloud height is estimated very accurately, as required by the algorithm, using simultaneous collocated Lidar measurements. High-resolution, both in space and time (4 min), cloud imageries are employed to minimize the errors in retrieved CMVs. The derived winds are evaluated against MST radar-derived winds by considering it as a reference. A very good correspondence is seen between these two wind measurements, both showing similar wind variation. The agreement is also found to be good in the both zonal and meridional wind velocities with RMSEs < 2.4 m s−1. At the end, the strengths and limitations of the algorithm are discussed, with possible solutions, wherever required.

scholarly journals The Capability of ENSEMBLES Models in Predicting the Principal Modes of Pan-Asian Monsoon Precipitation

2015 ◽  
Vol 28 (21) ◽  
pp. 8486-8510 ◽  
Author(s):  
Ya Gao ◽  
Huijun Wang ◽  
Dong Chen
Keyword(s):  
Asian Monsoon ◽  
Southern Oscillation ◽  
Summer Precipitation ◽  
Tropical Indian Ocean ◽  
Spatiotemporal Distribution ◽  
Monsoon Region ◽  
Coupled Models ◽  
Asian Monsoon Region ◽  
Second Mode ◽  
Ensembles Project

Abstract The predictability of the dominant modes of summer (June–September) precipitation in the pan-Asian monsoon region is evaluated based on 1-month-lead retrospective forecasts in five state-of-the-art coupled models from the ENSEMBLES project for the period 1979–2005. The results show that the models and their multimodel ensemble mean (MME) perform well in reproducing the interannual variability of the climatology and the spatiotemporal distribution of the first mode of summer precipitation in the pan-Asian monsoon region. The associated oceanic and atmospheric circulation indicators are also well captured, such as the spatiotemporal structures of the simultaneous El Niño–Southern Oscillation (ENSO) and Antarctic Oscillation in the Pacific Ocean (AAOSP). Moreover, the interannual variation of the preceding AAOSP can also be captured by some of the coupled models. For individual models, the ECMWF, Météo-France, and Met Office models exhibit better skill with respect to the first mode of summer precipitation in the pan-Asian monsoon region, which displays a tripole pattern from north to south over 80°–140°E. In addition, these models can successfully predict the intensity and location of the associated ENSO, as well as the simultaneous summer AAOSP distributions. By contrast, the prediction capabilities of the Leibniz Institute of Marine Sciences (IFM-GEOMAR) and Euro-Mediterranean Center for Climate Change (CMCC-INGV) models are relatively weaker. Furthermore, the predictions of the second mode of the summer precipitation in the pan-Asian monsoon region are investigated. Some of the ENSEMBLES models show good capability in predicting the spatiotemporal distribution of the second mode, owing to the successful prediction of the atmospheric convection activities over the tropical Indian Ocean.

scholarly journals A critical humidity threshold for monsoon transitions

2011 ◽  
Vol 7 (3) ◽  
pp. 1737-1765 ◽  
Author(s):  
J. Schewe ◽  
A. Levermann ◽  
H. Cheng
Keyword(s):  
Conceptual Model ◽  
Monsoon Rainfall ◽  
Reanalysis Data ◽  
Sea Surface ◽  
Specific Humidity ◽  
Critical Threshold ◽  
Monsoon Region ◽  
Proxy Records ◽  
Moisture Advection ◽  
Monsoon Strength

Abstract. Monsoon systems around the world are governed by the so-called moisture-advection feedback. Here we show that, in a minimal conceptual model, this feedback implies a critical threshold with respect to the atmospheric specific humidity qo over the ocean adjacent to the monsoon region. If qo falls short of this critical value qoc, monsoon rainfall over land cannot be sustained. Such a case could occur if evaporation from the ocean was reduced, e.g. due to low sea surface temperatures. Within the restrictions of the conceptual model, we estimate qoc from present-day reanalysis data for four major monsoon systems, and demonstrate how this concept can help understand abrupt variations in monsoon strength on orbital timescales as found in proxy records.

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