17 research outputs found
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Extreme daily rainfall in Pakistan and north India: scale-interactions, mechanisms, and precursors
While much of India is used to heavy precipitation and frequent low-pressure systems during the summer
monsoon, towards the northwest and into Pakistan, such events are uncommon. Here, as much as a third of
the annual rainfall is delivered sporadically during the winter monsoon by western disturbances. Such events
of sparse but heavy precipitation in this region of typically mountainous valleys in the north and desert in
the south can be catastrophic, as in the case of the Pakistan floods of July 2010. In this study, we identify
extreme precipitation events (EPEs) in a box approximately covering this region (65â—¦
-78â—¦W, 25â—¦
-38â—¦N) using
the APHRODITE gauge-based precipitation product. The role of the large-scale circulation in causing EPEs
is investigated: it is found that, during winter, they often coexist with an upper-tropospheric Rossby wave
train that has prominent anomalous southerlies over the region of interest. These winter EPEs are also found
to be strongly colocated with incident western disturbances whereas those occurring during the summer are
found to have a less direct relationship. Conversely, summer EPEs are found to have a strong relationship
with tropical lows. A detailed Lagrangian method is used to explore possible sources of moisture for such
events, and suggests that in winter, the moisture is mostly drawn from the Arabian Sea, whereas during the
summer, it comes from along the African coast and the Indian monsoon trough region
Anthropogenic Space Weather
Anthropogenic effects on the space environment started in the late 19th
century and reached their peak in the 1960s when high-altitude nuclear
explosions were carried out by the USA and the Soviet Union. These explosions
created artificial radiation belts near Earth that resulted in major damages to
several satellites. Another, unexpected impact of the high-altitude nuclear
tests was the electromagnetic pulse (EMP) that can have devastating effects
over a large geographic area (as large as the continental United States). Other
anthropogenic impacts on the space environment include chemical release ex-
periments, high-frequency wave heating of the ionosphere and the interaction of
VLF waves with the radiation belts. This paper reviews the fundamental physical
process behind these phenomena and discusses the observations of their impacts.Comment: 71 pages, 35 figure
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The impacts of climate change on the winter water cycle of the western Himalaya
Some 180 million people depend on the Indus River as a key water resource, fed largely by precipitation falling over the western Himalaya. However, the projected response of western Himalayan precipitation to climate change is currently not well constrained: CMIP5 GCMs project a reduced frequency and vorticity of synoptic-scale systems impacting the area, but such systems would exist in a considerably moister atmosphere.
In this study, a convection-permitting (4 km horizontal resolution) setup of the Weather Research and Forecasting (WRF) model is used to examine 40 cases of these synoptic-scale systems, known as western disturbances (WDs), as they interact with the western Himalaya. In addition to a present-day control run, three experiments are performed by perturbing the boundary and initial conditions to reflect pre-industrial, RCP4.5 and RCP8.5 background climates respectively.
It is found that in spite of the weakening intensity of WDs, net precipitation associated with them in future climate scenarios increases significantly; conversely there is no net change in precipitation between the pre-industrial and control experiments despite a significant conversion of snowfall in the pre-industrial experiment to rainfall in the control experiment, consistent with the changes seen in historical observations.
This shift from snowfall to rainfall has profound consequences on water resource management in the Indus Valley, where irrigation is dependent on spring meltwater. Flux decomposition shows that the increase in future precipitation follows directly from the projected moistening of the tropical atmosphere (which increases the moisture flux incident on the western Himalaya by 28%) overpowering the weakened dynamics (which decreases it by 20%).
Changes to extreme rainfall events are also examined: it is found that such events may increase significantly in frequency in both future scenarios examined.
Two-hour maxima rainfall events that currently occur in 1-in-8 WDs are projected to increase tenfold in frequency in the RCP8.5 scenario; more prolonged (one-week maxima) events are projected to increase fiftyfold