Mountain precipitation phase identification from multiple datasets

4 to 6 months, starting in spring 2022

Context : Identification of the precipitation phase (rain vs. snow) is a key parameter for forcing glacier surface mass balance models. The rain-snow temperature threshold has a large spatial variability, that is difficult to constrain due to a lack of measurements in some regions (Jennings et al., 2018). There is thus a need to better constrain the precipitation phase identification from high-altitude observations. Multiple direct precipitation instruments (OTT Parsivel2, Metek MRR2 ; see definition below) dedicated to the study of the precipitation phase are already running at three different locations (near Grenoble, near Zongo Glacier in Bolivia, in the Everest region in Nepal). Other instruments tipping bucket and weight gauge as well as albedometers will be used. The goal of this internship is to work on these different datasets in order to : 1- provide a climatology of the rain-snow temperature threshold for the Andean and the Himalayan sites ; 2- explore some methodological development for the validation of satellite radar data. We detail the two sub-sections of the internship below.

Part 1 : establish relationships between the proportion of hydrometeor types and the temperature
This work relies on the OTT Parsivel data collected over the past years in Bolivia and in Nepal. The candidate will first explore the hydrometeor classification provided by the instrument to validate its consistency (and potentially will explore the raw data spectra, depending on the success of this first analysis) and the link with the measured air temperature. Once this is done, the candidate will establish precipitation phase/temperature and analyze their annual cycle. This part is important to learn how to manipulate the data.

Part 2 : comparison of MRR (and OTT Parsivel) and GPM data around Grenoble
The goal of this second part is to evaluate the ability of GPM (Global Precipitation Measurements) satellite to detect the freezing level, and thus the elevation and thickness of the rain/snow transition in the atmosphere. The candidate will compare the MRR data acquired in winter 2019/2020 and winter 2020/2021 to the reflectivity profiles of GPM for selected precipitation events that are observed by GPM. The evaluation of GPM products will be conducted for selected events (approximately 20 per winter).

We seek for an enthusiastic candidate who is currently enrolled in a Master’s program in atmospheric sciences, earth sciences, or any other related topic. The internship is expected to last for 4 to 6 months. We encourage candidates with interest in quantitative data analysis and with curiosity to explore this rich dataset !

This internship if part of the ANR iFROG project. The candidate will thus benefit from a stimulating environment, and opportunities for his/her future plans.

OTT Parsivel2 (PARticle SIze and VELocity) : this instrument is a disdrometer. It is a laser system that measures the concentration, the fall velocity and the diameter of hydrometeors ; more details can be founds here : https://www.ott.com/fr-fr/produits/download/meteorological-technology-international-article/

Metek MRR2 (Micro Rain Radar) : this instrument is a vertically pointing Doppler K-band radar that measures vertical profiles of reflectivity and velocity ; https://www.biral.com/wp-content/uploads/2014/09/20110321_MRR.pdf

Jennings, K. S., Winchell, T. S., Livneh, B., and Molotch, N. P. : Spatial variation of the rain–snow temperature threshold across the Northern Hemisphere, Nat. Commun., 9, 1148, https://doi.org/10.1038/s41467-018-03629-7, 2018.