JWG C.5: Understanding the monsoon phenomenon from a geodetic perspective

Chair: Balaji Devaraju (India)
Vice-Chair: Matthias Weigelt (Germany)
(Affiliation: Commissions 2, 3 & 4, GGOS)

Introduction

The monsoon phenomenon is one of the large-scale atmospheric circulation processes that drives the water cycle affecting nearly one-third of the global population. It is predominantly acting in the Inter-Tropical Convergence Zone and it controls the agricultural productivity of the countries that fall within this region. Researchers from multiple disciplines have tried to understand and model the monsoon. A century of research efforts has led to a greater understanding of the monsoon phenomenon, but research gaps and open questions remain. Improved understanding will lead to better modelling of the monsoon as well as better forecasting, which will help mitigate some of the potential hazards and risks. Currently, meteorological forecasts on timing and duration of the monsoon, its strength, and its regional distribution are imited. Furthermore, it has been observed that ongoing climate change is linked to and alters the monsoon phenomenon. Many studies point to a weakening of the monsoon, which would mean reduced rainfall to the regions that it feeds. The consequences of such weakening could be disastrous and will threaten food and water security for the region. Therefore, it becomes imperative to observe, monitor and understand the monsoon with every possible means.

The bulk of research on monsoon has been mainly conducted by meteorologists, oceanographers, atmospheric and climate scientists with oceanographic, hydrological and hydrometeorological datasets and modelling. In the recent years, geodetic sensors have been recognized as a very insightful tool for studying climate processes and their spatio-temporal changes. This has been made possible by the increased accuracy and spatial coverage of geodetic sensors, which has enabled detecting the response of the Earth's shape and gravity field to climate-related processes. At the same time  geodetic sensors and their data have become integral to Earth system science, and represent critical monitoring tools. Of all geodetic methods satellite altimetry, satellite gravimetry and GNSS positioning have contributed significantly towards understanding sea level change, sea ice change, ice sheet and glacier mass balance, and the hydrological cycle, to name a few. Further, they have opened new pathways in Earth system science including the demand for improved ground networks for calibration. With the advent of satellite-based GNSS reflectometry, geodetic sensors are providing observations of soil moisture and wind speed at unprecedented horizontal scale and temporal resolution.

There is currently a deluge of geodetic sensor data spanning periods of 20 to 100 years, and therefore, perfectly suitable for climate change analysis. It presents a great opportunity to explore the signatures of various environmental and geophysical phenomena. The monsoon is one such phenomenon whose signatures in geodetic sensor data have largely remained underexplored. Some attempts have been made in the past to use geodetic sensor data in monsoon research. For example, satellite altimetry has been used to estimate the geostrophic contribution of monsoon currents. Similarly, precipitable water vapour estimates from continuously observing GNSS stations have been used to study the variations in monsoon precipitation. Nevertheless, the full integration of geodetic sensors data into monsoon modelling has not be achieved yet.

In this context we like to propose a working group to analyse geodetic sensor data in order to identify geodetic variables that are sensitive to the monsoon process, and the signatures that the monsoon leaves in geodetic data. Furthermore, we would like to explore the possibilities of complementing/supplementing monsoon forecast models, and thereby, improve their efficacy. The geodetic sensors to be used include, but are not limited to, satellite altimetry, continuously operating GNSS stations, tide gauges, gravimetric satellites (for example, GRACE, GRACE-FO and SLR), interferometric/polarimetric SAR, and terrestrial gravimeters. We will complement the geodetic sensors with meteorological data, remote sensing data and reanalysis products in global and regional climate models (such as PRECIP, BCC-CSM1.1, ECMWF-SYS4, NCEP-CFS2) to achieve our objectives.

Objectives

• Identify geodetic sensors, and in turn their observables, that are most sensitive to the monsoon phenomenon
• Identify the signatures (amplitudes, scales) of the monsoon phenomenon in geodetic sensor data
• Study the evolution of the monsoon phenomenon in time and space through geodetic sensor data
• Identify limitations and/or the necessity for additional and/or more accurate measurements including in situ networks
• Quantify the sensitivity to error sources, for example, tidal or non-gravitational force modelling
• Compare geodetic sensor data with reanalysis products in global and regional climate models
• Identify the possibility of assimilating geodetic sensor data into monsoon prediction models
• Understand relationships between extreme events and the monsoon phenomenon

Program of Activities

• Participate actively in IAG, AGU, AOGS and EGU conferences and organize sessions
• Organize working group meetings, splinter group meetings at the said symposia
• Collate geodetic sensor data along with their quality information and enable public accessibility via web services
• Conduct dedicated workshops and seminars on monsoon research with focus on geodetic sensor data
• Organize a special issue in a journal or an edited book

Members

• Alexander Braun (Canada)
• Karim Douch (Germany)
• Vagner G. Ferreira (China)
• Qiang Chen (Luxembourg)
• Subimal Ghosh (India)
• Zhizhou Liu (Hong Kong)
• Chandrakanta Ojha (USA)
• Mohammad Sharifi (Iran)
• Alka Singh (USA)
• Nico Sneeuw (Germany)
• Shivam Tripathi (India)
• Bramha Dutt Vishwakarma (UK)
• Susanna Werth (USA)
• Peng Yuan (Germany)