The Indian Summer Monsoon [ISM] provides approximately 80% of South Asia’s annual average precipitation. Nepal represents a particularly important sector of the ISM because of its location at the base of the Himalayas, Asia’s water tower, and in the zone of influence of the mid-latitude westerlies. Late Holocene ISM variability has previously been examined using high resolution resolved stable isotope records of stalagmites from northern, northeastern, and central India, but as of yet, no such records have been published from Nepal. We present high resolution stable isotopic time series from two precisely-dated and partially overlapping stalagmites spanning the last 2400 years from Siddha Baba Cave, central Nepal, as well as a year of isotopic data from rainwater collected near the cave. It has been suggested that the amount effect has only a minor effect on the oxygen isotope variability in precipitation in this area. As a result, we couple oxygen and carbon isotopes from these stalagmites to examine both regional and local-scale ISM dynamics. The Siddha Baba record reveals two periods suggestive of changes in the ISM: an apparent increase in rainfall during approximately CE 1350-1550 and a reduction in rainfall characterizing the last two centuries. We investigate these intervals using the Last Millennium Ensemble, a state-of-the-art suite of climate model simulations conducted by the National Center for Atmospheric Research with the Community Earth System Model. A primary focus is on links between Indo-Pacific ocean-atmosphere interactions and subsequent changes in the monsoon circulation over the Indian subcontinent, as well as regional moisture transport into Nepal between these periods.
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Constraining Emissions of Volatile Organic Compounds Over the Indian Subcontinent Using Space‐Based Formaldehyde Measurements
India is an air pollution mortality hot spot, but regional emissions are poorly understood. We present a high‐resolution nested chemical transport model (GEOS‐Chem) simulation for the Indian subcontinent and use it to interpret formaldehyde (HCHO) observations from two satellite sensors (OMI and GOME‐2A) in terms of constraints on regional volatile organic compound (VOC) emissions. We find modeled biogenic VOC emissions to be overestimated by ~30–60% for most locations and seasons, and derive a best estimate biogenic flux of 16 Tg C/year subcontinent‐wide for year 2009. Terrestrial vegetation provides approximately half the total VOC flux in our base‐case inversions (full uncertainty range: 44–65%). This differs from prior understanding, in which biogenic emissions represent >70% of the total. Our derived anthropogenic VOC emissions increase slightly (13–16% in the base case, for a subcontinent total of 15 Tg C/year in 2009) over RETRO year 2000 values, with some larger regional discrepancies. The optimized anthropogenic emissions agree well with the more recent CEDS inventory, both subcontinent‐wide (within 2%) and regionally. An exception is the Indo‐Gangetic Plain, where we find an underestimate for both RETRO and CEDS. Anthropogenic emissions thus constitute 37–50% of the annual regional VOC source in our base‐case inversions and exceed biogenic emissions over the Indo‐Gangetic Plain, West India, and South India, and over the entire subcontinent during winter and post‐monsoon. Fires are a minor fraction (<7%) of the total regional VOC source in the prior and optimized model. However, evidence suggests that VOC emissions in the fire inventory used here (GFEDv4) are too low over the Indian subcontinent.
more » « less- NSF-PAR ID:
- 10375640
- Publisher / Repository:
- DOI PREFIX: 10.1029
- Date Published:
- Journal Name:
- Journal of Geophysical Research: Atmospheres
- Volume:
- 124
- Issue:
- 19
- ISSN:
- 2169-897X
- Page Range / eLocation ID:
- p. 10525-10545
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
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The Indian Summer Monsoon [ISM] provides approximately 80% of South Asia’s annual average precipitation. Nepal represents a particularly important sector of the ISM because of its location at the base of the Himalayas, Asia’s water tower, and in the zone of influence of the mid-latitude westerlies. Late Holocene ISM variability has previously been examined using high resolution resolved stable isotope records of stalagmites from northern, northeastern, and central India, but as of yet, no such records have been published from Nepal. We present high resolution stable isotopic time series from two precisely-dated and partially overlapping stalagmites spanning the last 2400 years from Siddha Baba Cave, central Nepal, as well as a year of isotopic data from rainwater collected near the cave. It has been suggested that the amount effect has only a minor effect on the oxygen isotope variability in precipitation in this area. As a result, we couple oxygen and carbon isotopes from these stalagmites to examine both regional and local-scale ISM dynamics. The Siddha Baba record reveals two periods suggestive of changes in the ISM: an apparent increase in rainfall during approximately CE 1350-1550 and a reduction in rainfall characterizing the last two centuries. We investigate these intervals using the Last Millennium Ensemble, a state-of-the-art suite of climate model simulations conducted by the National Center for Atmospheric Research with the Community Earth System Model. A primary focus is on links between Indo-Pacific ocean-atmosphere interactions and subsequent changes in the monsoon circulation over the Indian subcontinent, as well as regional moisture transport into Nepal between these periods.more » « less
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