Manukumar Balaraman ChE-494 Date : 5/4/2015A Study On the Role Of Aerosols On Indian summer Monsoon Rainfall Using Satellite data.

For the Partial fulfillment of ChE- 494 Course (Chemistry of Global Climate Change)

Submitted By

Manukumar Balaraman Arizona State University

Table of Content Page no Abstract 3

Introduction4

Synthesis5 Result and Discussion9 Conclusion and Recommendation 11

Appendix 13

A Study On the Role Of Aerosols On Indian summer Monsoon Rainfall Using Satellite data.

Abstract

It is very challenging and critical for understanding the role of aerosols on clouds life time and summer monsoon rainfall. Indian summer monsoon rainfall is the main source for the fresh water supply for the vast population in the Indian continent, and also it is the most important rainfall that influences the economic and agriculture production and other water related social sector in the Asian subcontinent2. There are a number of studies conducted on the role of aerosols on Indian summer monsoon rainfall. That is these studies indicate that aerosol can alter the monsoon rainfall. It results from a complex interaction of heating from radiation and its interactions with aerosols in a complex level. Atmospheric aerosols are solid or liquid particles that vary in their sizes, shapes, composition as well as optical properties. They can affect cloud properties, water cycle, radiation effect on the planet and so on. High winds acts as a source and conduit of natural and continental aerosol. Aerosols can affect the Summer Monsoon in multiple levels. There are multiple research studies that are done to understand these effects. Studies have shown that Monsoon rainfalls that occur the mid year are strongly correlated with aerosol levels over West Asia, North Africa and the Arabian Sea. In other words, the aerosol content in the atmosphere can play a major role in causing monsoon floods or draughts in India3.

IntroductionWhen combining India and China, 60% of the worlds population lives in the Monsoon region. Indian Summer Monsoon Rainfall starts from early week June to last week of September every year. Around 90% Indian Summer Monsoon Rainfall receives in central and western India. This rainfall is the backbone of Indian agriculture production2. It has a tremendous impact on Indian food production as well as water resource management and other sensitive industries in the Indian subcontinent5. Thus it is very important for the prediction of Indian summer Monsoon and has become a serious topic of scientific research more than ten years. Indian Summer Monsoon Rainfall is affected by different internal and external factors. Aerosols are one of the most influential components among them6. The two main environmental hazards in this area are, Monsoon related droughts and floods, and aerosols7.Atmospheric aerosols are solid or liquid particles suspended in air. They differ in their composition, size, shapes, and optical properties. There are two types of aerosols- man made and natural. The man made aerosols are mainly from pollution- vehicles, industries and so on. The natural aerosols form from forest fires, deserts and so on. Aerosols have direct and indirect effects on the climate. Some of these effects are still not clear to man; there are a number of research studies being conducted to understand the effect2. Researchers have been utilizing the help of satellites and sensors to understand more on this1. One of the major direct effects of aerosol is the absorption or scattering of solar radiation. This has a direct impact on global warming as well as green house effect. Some of the indirect effects are altered regional water cycle, warm rain suppression, and increased cloud life cooling. But most of these effects are not fully understood or even know to man3!!!Aerosol may also reduce the Indian summer monsoon rainfall by cooling the surface by shadowing the solar radiation that is it reduce the solar radiation by reaching the earth surface this effect is called Solar Dimming Effect (SDM). Due to this effect the reduction of theremal contract in the southern part of the India and resulting cut down the local monsoon4. In his study Dr . Lau called this effect a the Elevated Heat pump hypothesis. Which point that the accumulation of black carbon from Indo-Gangetic Plain may induced warming in the upper troposphere and this lead to increased rainfall over the north and central part of India in the early summer that is March last to April5. A secondary effect increased rainfall and also there will be an associated changes in the cloud and hydrological cycle this affect the reduction of monsoon rain in the late summer6. Effects of Aerosol on the Climate in Asian Region : Indian climate is not the only one that is affected; aerosol has made an impact on the Tibetan plateau, Bhutan, Nepal and China. Because of the heating effect of the aerosol, there has been increased warming to the Tibetan Plateau and accelerated melting of the snow from the western Tibetan Plateau and the Himalayas. Aerosols also cause the snow darkening effect- the black carbon and dust on the snow makes the snow darker4. Darker surface absorbs sunlight and get heated up, thus resulting in melting of the snow. This is occurring in the Himalayas as well as in the Tibetan plateau. This has resulted in spontaneous floods from the glaciers, shortage of fresh water as well as power, soil erosion, loss of bio diversity and a highly stressed and vulnerable ecosystem. Studies have also shown that there has been a significant reduction in the monsoon in Eastern China because of increased aerosol from air pollution3.

SynthesisThere are multiple research studies available that are done on the effect of aerosol on the climate especially on the Summer monsoon2. NASA conducted one of the major studies in 2010. In this study, Dr. William Lau states that the soot in the aerosol and dust result in mid- tropospheric radiative heating along the Himalayas causing rise in temperature in Northern India, which in turn results in increase in middle and upper tropospheric temperature over Tibetan Plateau causing early snow melt4. He also state that the aerosol impact on summer monsoon rainfall are strongly depend on emission source and also on the transport and deposition by large-scale circulation10.

The data set used for this study is include GPCP (Global Precipitation Climatology Project) rainfall data, it is a satellite measurement data combined with a rain gauge data from the land. And this study also includes the aerosol index data from both Total Ozone Mapping Spectrometer (TOMS) and OMI for absorbing aerosol8. The aerosol index is used to observed the presence of UV absorbing aerosol such as soot and dust. The positive value of Aerosol index indicate that it is absorbing aerosol while the aerosol index is small or a negative number then it is a non-absorbing aerosol, this study also used the data from Micro sounding unit this is a tropospheric temperature data, and used the wind data for studying the circular wind pattern10. These data are strongly indicate that aerosol impact on Indian monsoon environment. For the positive rainfall trend in the central India in the month of May June is due to the increasing trend in the absorbing aerosol in the Indo-Gangetic Plain and there is a anticyclone wind pattern in the northwest India. And also there is a strong vertical shear across the Indian subcontinent, the early monsoon season may indicate the increase in cloud pattern will amplify the effect7. In the concluding part of this study Dr. William Lau state that the aerosol impact on monsoon rainfall strongly depend not only the emission source but also on the transport and deposition of large scale circulation9.

Another study conducted by R.L Bhawar and P.C Devare in 2006. In their study show the role of aerosol optical and micro-physical properties and their effect on the hydrological cycle of Indian summer monsoon rainfall7. This study help to have a clear picture of the important of aerosols in hydrological cycle on the regional scale this study mainly observe the central India. With the help of data received from the MICROTOPS-II solar radiometer and TOMS (Total Ozone Mapping Spectrometer). These space spectrometer provides a good temporal and spatial coverage from 1978. Total ozone Mapping Spectrometer is retrieving both incoming solar radiation and back-scattered UV radiance measurement, UV absorbing aerosol like dust smoke and soot produce small contract and negative residues and the non absorbing aerosol ike sea-salt and sulfate produce greater contrast and negative residue so TOMS data is particularly used for the modulating the aerosol index9. The solar radiometer is used to observed the aerosol optical depth data and with the help of Total ozone Mapping Spectrometer (TOMS) aerosol index data with this data they recorded two concurrent metrological parameter for two successive monsoon seasons from 2004 and 2005 over the central India and they found that the vertical and horizontal temperature variation can affect the seasonal rainfall. The cloud formation will mostly depend on the concentration of aerosol but the activation process is not monotonic10. The initial cloud formation is helping by the surface metrological features. And another feature they found is that the surface temperature were high during the pre-monsoon season that leading to increase the optical depth of aerosol due to the effect of high speed surface wind. And they conclude that the aerosol influence on Indian summer monsoon rainfall mainly depend on the dynamics or microphysics or both. In their study aerosol impact on the hydrological cycle is due to their properties like scattering and absorbing and mixing and transport properties it also affect their composition and location of the aerosol loading. And they conclude that it is very difficult to generalize the impact of aerosol on the summer hydrological cycle, this type of studies need dense network of observation9. And in their study they also views that there are large variation in the hydrological circle when the aerosol index vale is weak this phenomena is observed during the 2004 summer monsoon rainfall the aerosol index received from the TOMS satellite is weak and the total percentage of the rainfall on that year is less compared to the previous year, so it is clear that the aerosol index have some impact on the cloud formation and this cloud formation is one of the reason for the hydrological cycle which cause the precipitation during the summer times8.

Third and final study describe here is conducted by Ravi Kiran in 2010 using MODIS data (moderate- resolution imaging spectra radio meter) this study used past 10 year aerosol index data for the modulation of the Indian summer monsoon rainfall, for this study he used past ten year data that is from 2000 to 2009, in this study the variations of cloud and aerosol properties over the Indian region in associated with the intraseasonal variations of Indian Summer Monsoon Rainfall9. His main observation is that during the break spells, aerosol loading from the north Arabian Sea is transported to Central India and the increase in aerosol content decreases the indirect effect of aerosols on cloud properties. As per this studies the circulation during break spells followed by the active cases helps in the accumulation of absorbing aerosols over Central India, results in the increase of Aerosol index and the meridional gradient of temperature at low level between aerosol - rich Central India and pristine equatorial Indian Ocean is large which can sustains for long time during this leading to significant moisture convergence to Central India. Using the pentad-resolution observational datasets, analyzed the interannual variations of absorbing aerosols and related hydrometeorology over South Asia in the pre-monsoon period and noticed the complex interplay among aerosols, dynamics and precipitation also shows the challenge of extracting the aerosol impact from an observational analysis6.Location of the Indian Summer Monsoon Rainfall Study Region : Table -1 in Appendix C shows the exact place location that is it include the Longitude and latitude of the place where the all three above study conducted. All the above study considered the variation of aerosol characteristic like aerosol optical depth, aerosol index and cloud parameter etc, and these study used past ten year data that is from the year 2002 to 2012 for the aerosol-cloud parameter. Among the above three place extensive studies are conducted in the central India because in central India is loaded with substantial amount of aerosol concentration due to the increased air pollution these area received more rainfall in the Indian Summer Monsoon Rainfall season compared to other part of the Indian sub content, there for these region has been selected for the intraseasonal variation in aerosols and Indian Summer Monsoon Rainfall8.Result and Discussion: All the recent study model develop for the Indian summer monsoon rainfall are imperfect, and they have the difficulty in simulating all aspects of these correlations. But these studies can provide significant insight into the working of the complex climate system8. These model develop different configurations of the Community Atmosphere Model and have been used to expose, the physical mechanism behind the observed and modeled relationships4. These model includes treatments of the different aerosols species and their precursors for affecting the summer monsoon rainfall like dust, black organic carbon, sea-salt, and sulfate3. Aerosols affect both ice and liquid microphysics of clouds in the model and the radiative transfer calculation. As with most global climate models, aerosols do not directly affect the Community Atmosphere Model convective cloud parameterizations microphysics, but convection does respond to aerosol radiative forcing as it affects stability and the surface buoyancy fluxes8. The correlation between central and northern Indian summer monsoon precipitation and Aerosol Optical Depth have positive correlation extends over a much larger area, covering the whole of Arabian Sea, Bay of Bengal and northern of India. Modest changes to meteorology can have a large impact on the aerosol spatial distribution, but the model physical parameterizations do reproduce the general correlation pattern, positive over Arabian Sea and negative over Northeast India3. Additional simulations have also been made removing sea-salt, dust and anthropogenic aerosol sources individually, and in combination. Exclusion of these combinations of sources helps to determine the cause for the observed correlation patterns. A statistically significant relationship exists over the Arabian Sea with anthropogenic aerosol sources when sea-salt and dust emissions are individually excluded. However, when both dust and sea-salt are removed, the amplitude of the correlation decreases and statistical significance disappears, indicating that both sea-salt and dust aerosols together contribute to the observed pattern. This also implies that anthropogenic aerosols alone are not responsible for the correlations5. Both artificial aerosol like dust and the natural aerosol like sea salt influence clouds life time and hydrological cycle and radiative heating. If we try to remove one species from this may have an impact on the others. In the model if we try to remove one species that is the dust source then this leads to a complete disappearance of the correlation or there will be some change in the observed correlations. When we try to remove the sea-salt sources, the simulations will disappears permanently so from this hypothesis it is clear that the observed correlations can be reproduced only when dust is present along with either sea-salt or anthropogenic aerosols. In the model there are different species of aerosol are affecting the summer rainfall in the southern part of India there are lot of natural sea-salt aerosol presentation in the cloud this may be the one reason for the rainfall in the southern part, these natural aerosol are from the Arabian sea6. But the opposite of this behavior is found on central India2. So there is an increased precipitation over central India is correlated with increased dust aerosols over Arabian Sea or West Asia. When the dust concentration of the west Asian region decrease the central Indian precipitation drops drastically2. When we used independent satellite retrievals to aerosol index data and found that there is a strong correlation between Arabian Sea Aerosol Optical Depth and Indian monsoon precipitation occurring on short timescales. Conclusion and Recommendation: Aerosols are a major source of uncertainty in both attributions of past and future climate changes. This because of their short lifespan and the numerous ways they interact with other elements in the climate system. In the above-mentioned studies, it is proven that there is a direct connection between the aerosol and rainfall variability7. It proves that there is significant links between cloud-aerosol-precipitation relations that directly and indirectly affects the Monsoon rainfalls. Satellite observations are a useful tool to assess aerosol impacts on the Asian Summer Monsoon. The quantification and localization of aerosol occurrence above and around the Tibetan Plateau and their use as input data for a radiative transfer model help to evaluate the different theories2.

During the active spells of rainfalls, the aerosols are mostly seen over the northeastern Arabian Sea, and there is a significant reduction in the Central India. During the break spells of the rain, the aerosols are confined over the Himalayan foothills5. This proves that the aerosol characteristics also need to be taken into consideration when analyzing the impact on Monsoon. Atmospheric heating by absorbing aerosol causes an advance and intensification of Indian summer monsoon8.The heating in the upper troposphere over the Tibetan plateau during April- May results in the advancement of monsoon. Absorbing the aerosol, which is dense in black carbon and dust, causes this8. This results in the troposphere acting as an elevated heat pump, which in turn causes an enhanced convection of warm air thus causing increased summer monsoon rainfalls over north India. This effect indicates the importance of radiative and sensible heat flux over the Tibetan plateau in the evolution of the Asian summer monsoon9.Analyzing the aerosol impact on Indian summer monsoon rainfall itself is a very challenging research as the composition of aerosol varies constantly7. More data collection and research need to be conducted regarding cloud parameters, inter annual variations in aerosol and rainfall as well as other meteorological factors. Detailed analysis of inter connection between rain, aerosol and cloud parameters another area that needs to be researched on10. Also studies need to be conducted to understand and find explanation for the underlying mechanism of aerosol- cloud-rain interlink.Indirect effects of aerosols are still a subject of intense research. More information is required to understand aerosol-monsoon-water cycle interaction. New avenues of monsoon variability and predictability need to be researched10.

Reference[1]Ajith Kumar, 2013. Variability of aerosol optical depth and cloud parameters over Central Indian regions retrieved from MODIS satellite data. Journal of Atmospheric and Solar-Terrestrial Physics 150201(2013)2439. doi.org/10.2016/j.jastp.2013.03.025. [2]SDey, S., Manider Singh, R.P., 2002. Retrieval of aerosol parameters using IRS P4 OCM data over the Arabian Sea and the Bay of Bengal. Current Science vol. 93, NO. 120. [3]Akonwar, M., CParekh, A., Swami, B. N.,2012. Dynamics of South-West Indian summer monsoon rainfall trends in recent decades. Geophysical Research Letters 39, L10708. http://dx.doi:10.1029/2012GL052018. [4]K.Murthy, V., Smerhukla, J., 2007.Intra seasonal and Inter Seasonally Patterns of Indian Monsoon Rainfall .Journel of Climate 20, 320. [5]Manoj Kumar, M.G M., Devara, B.C.S., Joseph, S.K, Sahai, D.K., 2013. Aerosol indirect effect on Indian Summer Monsoon 60, 153e163. [6]Rama nathan, V., Wu, G.-X., Li, Z., Tsay, Chen, Y., Huang, J., Taniguchi, K., Zhang, R., 2008. The new challenge for monsoon climate research. pp 369-383.doi: 10.1175/bams-89-3-369.[7] Cautam, R., Dasu, N.C., Lau, K.M., Kcafatos, M., 2009b. Aerosol and rainfall variability over the Indian monsoon region:. 29: 36913703. [8]Goswami, B.N., Ajaya Mohan, R.S., 2001.Intraseasonal oscillations and interannual variability of the Indian summer monsoon. Journal of Climate 14, 1180e1198. [9]Mrandey, B. S., Dtier, P., Wagner, T. M .,2013.Investigating relationships between Aerosol Optical Depth and Indian summer monsoon rainfall using satellite data, 13, 31773184, 2013.doi:10.5194/acp-13- 3177-2013. [10]S., Hansen, J., Cazarenko, L. & Luo, Y. F. Climate effects of carbon aerosols in Central India and Southern Asia. Science 497, 2210-2353 (2002).

Appendex-A : Aerosol affects the climate system mainly through direct radiative effects, the following figure explain the Different processes involved in the aerosol and rainfall interactions1.

Figure -1 : Different processes involved in the aerosol and rainfall interactions1

Appendix B : Impact of aerosol on rainfall. The figure below shows that the different types of aerosol interact the Indian summer monsoon rainfall and also explain the cloud albedo and life time of the cloud7.

Figure 2 : Impact of aerosol on rainfall7

Appendix C: Table : 1 Location of the Indian Summer Monsoon Rainfall Study Region5 Study Region Latitude Longitude

Arabian Sea 150-180N 600 -680 E

Bay of Bengal 150-180 N 830-900 E

Central India 130-260 N 700-790 E

Figure 3 : Satellite data for the correlation coefficient between precipitation and aerosol optical depth over the Indian region4.

3May 5, 2015