1,720,970 research outputs found
Impact of Tropical Volcanic Eruptions on Hadley Circulation Using a High-Resolution AGCM
Get PDFThe direct radiative effects of volcanic eruptions resulting in solar dimming, stratospheric warming, global surface cooling and reduction in rainfall are well documented. However, eruptions also cause indirect climatic impacts that are not well understood. For example, solar dimming induced by volcanic aerosols could cause changes in tropical Hadley circulation that in turn largely affect evaporation and precipitation patterns. Therefore, understanding the sensitivity of HC to volcanism is essential, as this circulation is directly related to precipitation changes in the tropics and with other large-scale circulations. Hence, to better understand the post-eruption sensitivity of HC and associated changes in the hydrologic cycle, simulations for the El Chichón and Pinatubo tropical eruptions were conducted using a high-resolution atmospheric model (HIRAM), effectively at 25 and 50 km grid spacing. The model simulated results are then compared with observational and reanalysis products. Both the model and observational analysis show posteruption weakening, shrinking and equatorward displacement of the updraft branch of HC caused by the equatorward shift of midlatitude jets and hemispheric land-sea thermal gradient. The Intertropical Convergence Zone (ITCZ) is tightly coupled to the rising branch of HC, hence, post-eruption weakening and equatorward displacement of HC cause weakening of ITCZ that adversely affects rainfall distribution in the monsoon-fed regions, especially the South Asian and African tropical rain-belt regions. The modelproduced post-eruption distribution of cloud contents suggests a southward shift of ITCZ. The HIRAM results are largely in agreement with the reanalysis, observations and previous studies indicating that this model performs reasonably well in reproducing the global and regional-scale dynamic changes caused by volcanic radiative forcing.I thank Earth Science and Engineering Department, King Abdullah University of Science and Technology, Thuwal, Saudi Arabia for providing computational facilities that were used to conduct model simulations. The observational and simulation results are available from the author upon reques
The Sensitivity of DTR to the Increased CO2 over Mid-latitude Semi-dry Regions
No full textThe rationale for this study lies in the fact that the mid-latitude regions are largely affected by the global and regional scale circulation changes. Moreover, earlier studies emphasize that the variation in atmospheric concentration of heat-trapping gases, cloud amount and moisture contents produce substantial regional climatic changes. Therefore, it is of significant practical importance to analyze the sensitivity of midlatitude regions to anthropogenic forcing, especially, the CO2 radiative forcing. This study assesses the role of CO2 radiative forcing in causing asymmetric diurnal changes over the mid-latitude semi-dry region using an idealized experiment conducted by single column (1-D) RadiativeConvective Model (RCM) of the diurnal cycle. The model is capable enough in highlighting the main features responsible for the observed diurnal asymmetry in the ground temperature. A significant decrease in the Diurnal Temperature Range (DTR) is observed in this region under doubled CO2 forcing. The amount of thermal radiation trapped by CO2 forcing in the presence of water vapors plays a key role in surface temperature changes and resultant decreasing of the DTR. It is further found that CO2 induced climatic feedbacks are equally important in producing diurnal asymmetry. To better understand the complete picture of the DTR variability, one needs to explore all the possible forcing and feedbacks such as caused by aerosols, water vapors and cloud amount along with their distribution in the atmosphere.The author would like to thank Prof. Georgiy Stenchikov, Chairman, Earth Science and Engineering Department, King Abdullah University of Science and Technology for providing access to his single column RCM used in this study
Revisiting the strong and weak ENSO teleconnection impacts using a high-resolution atmospheric model
Get PDFTo evaluate the performance of a high-resolution atmospheric model (HiRAM) and to improve our understanding of the climatic impacts of ENSO forcing and associated teleconnections, we analyzed AMIP-style HiRAM simulations conducted effectively at 25 km grid spacing. To better assess HiRAM response to ENSO climate variability; we categorized it into strong and weak El Niño/La Niña episodes. The HiRAM model reproduced the impacts of strong ENSO over global scale very well, however, it underestimated ENSO teleconnection patterns and associated changes over regional scale (e.g., MENA and South Asia), especially following weak ENSO that could be attributed to model weak response to circulation changes such as Pacific North American (PNA) and North Atlantic Oscillation (NAO). Moreover, our results emphasize that ENSO impacts are relatively stronger over the Inter-Tropical Convergence Zone (ITCZ) compared to extra-tropics and high-latitude regions. The positive phase of ENSO causes weakening in rainfall over the African tropical rain-belt, parts of South and Southeast Asia. Both the reanalysis and HiRAM results reveal that ENSO-induced negative (positive) NAO-like response and associated changes over Southern Europe and North Africa vary significantly following the increased intensity of El Niño (La Niña). We further found that the ENSO magnitude significantly impacts Hadley and Walker circulations. The El Niño phase of ENSO overall strengthens the Hadley Cell, and the reverse is true for the La Niña phase. This ENSO-induced strengthening and weakening of Hadley Cell induce significant impact over South Asian and African convective regions through modification of the ITCZ circulation system
Analysis of Climate Trends and Leading Modes of Climate Variability for MENA Region
No full textThe Middle East and North Africa (MENA), primarily the Arabian Peninsula (AP) is a region where the rate of mean surface temperature rise per decade is among the highest globally known during the recent past. Moreover, MENA regional climate is very sensitive to internal and external climate drivers. Therefore, it is of significant practical importance to analyze MENA sensitivity to climate trends as well as leading variability modes such as El Nino Southern Oscillation (ENSO), North Atlantic Oscillation (NAO) and Indian summer monsoon (ISM). Using multiple regression technique on observations and the high-resolution atmospheric model (HiRAM) output, this study investigates the role of climate trends, and leading circulation modes such as NAO, ENSO, and ISM in inducing temperature and precipitation variability in MENA region for the period 1979-2008. Our results show substantial regional temperature and precipitation responses of ENSO, NAO, and ISM over MENA. Both the model and the observations indicate that positive phase of NAO and ENSO significantly cools central parts of MENA, in particular, the AP in winter. However, in boreal summer, the warm ENSO phase produces significant warming and drying over the tropical region. The strengthening (weakening) of ISM suggests cooling (warming) and wetting (drying) over MENA rain-belt region. Moreover, ISM induces a dipole precipitation structure over the tropics caused by ITCZ shift and associated cloud distribution. HiRAM slightly underestimates NAO and ENSO winter cooling over the AP, however; overall patterns are well reproduced. The conducted analysis sheds light on the internal mechanisms of MENA climate variability.The King Abdullah University of Science and Technology (KAUST), Thuwal, Saudi Arabia supported the research reported in this publication. The GFDL-HIRAM simulation data can be accessed from http://nomads.gfdl.noaa.gov:8080/DataPortal/cmip5.jsp. The UDEL observations dataset used in this study is provided by the NOAA/OAR/ESRL PSD, Boulder, Colorado, USA, through their web site at http://www.esrl.noaa.gov/psd
Regional Climate Response of Middle Eastern, African, and South Asian Monsoon Regions to Explosive Volcanism and ENSO Forcing
No full textDecadal Climate Variability and Predictability
No full textA report on the 'CLIVAR-ICTP Workshop on Decadal Climate Variability and Predictability (DCVP) 2015' held at the Abdus Salam International Centre for Theoretical Physics (ICTP) Trieste, Italy during 16–24 November 2015 and organized by ICTP in association with Climate Variability and Predictability (CLIVAR), NOAA (National Oceanic and Atmospheric Administration, US Department of Commerce) and PAGES (Past Global Changes) and both parts of this scientific event (lectures and lab sessions) were cosponsored by World Climate Research Programme (WCRP), The Chinese University of Hong-Kong, Institute of Environment Energy and Sustainability (IEES).S.A. thanks Prof. Sunil Bajpai (Director, Birbal Sahni Institute of Palaeobotany (BSIP), Lucknow) for permission
(BSIP/RDCC/Publication no. 71/2015-16) to publish this report; Dr Pawan Govil and Dr Md. Firoze Quamar (BSIP,
Lucknow) for their encouragement. S.A. also thanks to ICTP, Trieste, Italy for fund support. Whereas M.M.D. thanks KAUST, Saudi Arabia for providing financial assistance to
attend the workshop
Study of the global and regional climatic impacts of ENSO magnitude using SPEEDY AGCM
No full textENSO is considered as a strong atmospheric teleconnection that has pronounced global and regional circulation effects. It modifies global monsoon system, especially, Asian and African monsoons. Previous studies suggest that both the frequency and magnitude of ENSO events have increased over the last few decades resulting in a need to study climatic impacts of ENSO magnitude both at global and regional scales. Hence, to better understand the impact of ENSO amplitude over the tropical and extratropical regions focussing on the Asian and African domains, ENSO sensitivity experiments are conducted using ICTPAGCM (‘SPEEDY’). It is anticipated that the tropical Pacific SST forcing will be enough to produce ENSO-induced teleconnection patterns; therefore, the model is forced using NINO3.4 regressed SST anomalies over the tropical Pacific only. SPEEDY reproduces the impact of ENSO over the Pacific, North and South America and African regions very well. However, it underestimates ENSO teleconnection patterns and associated changes over South Asia, particularly in the Indian region, which suggests that the tropical Pacific SST forcing is not sufficient to represent ENSO-induced teleconnection patterns over South Asia. Therefore, SST forcing over the tropical Indian Ocean together with air–sea coupling is also required for better representation of ENSO-induced changes in these regions. Moreover, results obtained by this pacemaker experiment show that ENSO impacts are relatively stronger over the Inter-Tropical Convergence Zone (ITCZ) compared to extratropics and high latitude regions. The positive phase of ENSO causes weakening in rainfall activity over African tropical rain belt, parts of South and Southeast Asia, whereas, the La Niña phase produces more rain over these regions during the summer season. Model results further reveal that ENSO magnitude has a stronger impact over African Sahel and South Asia, especially over the Indian region because of its significant impact over the tropical Atlantic and the Indian Ocean through Walker circulation. ENSO-induced negative (positive) NAO-like response and associated changes over Southern Europe and North Africa get significantly strong following increased intensity of El Niño (La Niña) in the northern (southern) hemisphere in the boreal winter (summer) season. We further find that ENSO magnitude significantly impacts Hadley and Walker circulations. The positive phase of ENSO (El Niño) overall strengthens Hadley cell and a reverse is true for the La Niña phase. ENSO-induced strengthening and weakening of Hadley cell induces significant impact over South Asian and African ITCZ convective regions through modification of ITCZ/monsoon circulation system.We would like to thank the editor and two anonymous reviewers whose constructive suggestions and comments significantly improved the manuscript. We are also thankful to the Abdus Salam International Centre for Theoretical Physics (ICTP), Trieste, Italy, for providing computational facilities and technical support to perform the experiments at ICTP computer lab. The first author is supported by King Abdullah University of Science and Technology (KAUST), Thuwal, Saudi Arabia. The simulation results and figures are available from the authors on request
Regional Climate Response to Volcanic Radiative Forcing in Middle East and North Africa
No full textWe have tested the regional climate sensitivity in the Middle East and North Africa (MENA) to radiation perturbations caused by the large explosive equatorial volcanic eruptions of the second part of 20th century, El Chichon and Pinatubo occurred, respectively, in 1982 and 1991. The observations and reanalysis data show that the surface volcanic cooling in the MENA region is two-three times larger than the global mean response to volcanic forcing. The Red Sea surface temperature appears to be also very sensitive to the external radiative impact. E.g., the sea surface cooling, associated with the 1991 Pinatubo eruption, caused deep water mixing and coral bleaching for a few years. To better quantify these effects we use the Geophysical Fluid Dynamics Laboratory global High Resolution Atmospheric Model (HIRAM) to conduct simulations of both the El Chichon and Pinatubo impacts with the effectively 25-km grid spacing. We find that the circulation changes associated with the positive phase of the arctic oscillation amplified the winter temperature anomalies in 1982-1984 and 1991-1993. The dynamic response to volcanic cooling also is characterized by the southward shift of the inter-tropical convergence zone in summer and associated impact on the precipitation patterns. Thus, these results suggest that the climate regime in the MENA region is highly sensitive to external forcing. This is important for better understanding of the climate variability and change in this region
- …
