Emily Collier

Precipitation Seasonality and Variability over the Tibetan Plateau as Resolved by the High Asia Reanalysis

AbstractBecause of the scarcity of meteorological observations, the precipitation climate on the Tibetan Plateau and surrounding regions (TP) has been insufficiently documented so far. In this study, the characteristics and basic features of precipitation on the TP during an 11-yr period (2001–11) are described on monthly-to-annual time scales. For this purpose, a new high-resolution atmospheric dataset is analyzed, the High Asia Reanalysis (HAR), generated by dynamical downscaling of global analysis data using the Weather Research and Forecasting (WRF) model. The HAR precipitation data at 30- and 10-km resolutions are compared with both rain gauge observations and satellite-based precipitation estimates from the Tropical Rainfall Measurement Mission (TRMM). It is found that the HAR reproduces previously reported spatial patterns and seasonality of precipitation and that the high-resolution data add value regarding snowfall retrieval, precipitation frequency, and orographic precipitation. It is demonstrat...

High‐resolution modeling of atmospheric dynamics in the Nepalese Himalaya

High-altitude meteorological processes in the Himalaya are influenced by complex interactions between the topography and the monsoon and westerly circulation systems. In this study, we use the Weather Research and Forecasting model configured with high spatial resolution to understand seasonal patterns of near-surface meteorological fields and precipitation processes in the Langtang catchment in the central Himalaya. Using a unique high-altitude observational network, we evaluate a simulation from 17 June 2012 to 16 June 2013 and conclude that, at 1 km horizontal grid spacing, the model captures the main features of observed meteorological variability in the catchment. The finer representation of the complex terrain and explicit simulation of convection at this grid spacing give strong improvements in near-surface air temperature and small improvements in precipitation, in particular in the magnitudes of daytime convective precipitation and at higher elevations. The seasonal differences are noteworthy, including a reversal in the vertical and along-valley distributions of precipitation between the monsoon and winter seasons, with peak values simulated at lower altitudes (~3000 m above sea level (asl)) and in the upper regions (above 5000 m asl) in each season, respectively. We conclude that there is great potential for improving the local accuracy of climate change impact studies in the Himalaya by using high-resolution atmospheric models to generate the forcing for such studies.

Sensitivity of simulated summer monsoonal precipitation in Langtang Valley, Himalaya, to cloud microphysics schemes in WRF

A better understanding of regional-scale precipitation patterns in the Himalayan region is required to increase our knowledge of the impacts of climate change on downstream water availability. This study examines the impact of four cloud microphysical schemes (Thompson, Morrison, WRF Single-Moment 5-class, and WRF Double-Moment 6-class) on summer monsoon precipitation in the Langtang Valley in the central Nepalese Himalayas, as simulated by the Weather Research and Forecasting (WRF) model at 1-km grid spacing for a 10-day period in July 2012. The model results are evaluated through a comparison with surface precipitation and radiation measurements made at two observation sites. Additional understanding is gained from a detailed examination of the microphysical characteristics simulated by each scheme, which are compared with measurements using a spaceborne radar/lidar cloud product. Also examined are the roles of large and small-scale forcing. n nIn general the schemes are able to capture the timing of surface precipitation better than the actual amounts in the Langtang Valley, which are predominately underestimated, with the Morrison scheme showing the best agreement with the measured values. The schemes all show a large positive bias in incoming radiation. Analysis of the radar/lidar cloud product and hydrometeors from each of the schemes suggests that ‘cold-rain’ processes are a key precipitation formation mechanism, which is also well represented by the Morrison scheme. As well as microphysical structure, both large-scale and localised forcing is also important.

Recent atmospheric variability at Kibo Summit, Kilimanjaro, and its relation to climate mode activity

AbstractAccurate knowledge of the impact of internal atmospheric variability is required for the detection and attribution of climate change and for interpreting glacier records. However, current knowledge of such impacts in high-mountain regions is largely based on statistical methods, as the observational data required for process-based assessments are often spatially or temporally deficient. Using a case study of Kilimanjaro, 12 years of convection-permitting atmospheric modeling are combined with an 8-yr observational record to evaluate the impact of climate oscillations on recent high-altitude atmospheric variability during the short rains (the secondary rain season in the region). The focus is on two modes that have a well-established relationship with precipitation during this season, El Nino–Southern Oscillation and the Indian Ocean zonal mode, and demonstrate their strong association with local and mesoscale conditions at Kilimanjaro. Both oscillations correlate positively with humidity fluctuati...

Prominent Midlatitude Circulation Signature in High Asia's Surface Climate During Monsoon

Author(s): Molg, T; Maussion, F; Collier, E; Chiang, JCH; Scherer, D | Abstract: