Calibration and validation studies over the North Atlantic and UK for the Global Precipitation Mission

Lead Research Organisation: University of Leicester
Department Name: Physics and Astronomy


Understanding the changing global precipitation patterns that result from a changing climate represents one of the great research priorities of the next decades. In order to better define the future we need to understand the present and the inter-annual variability of the precipitation cycle, which mirrors, in short periods, the expected climate-change-induced long-term variability. However, while observational studies based on the past 30 year records suggest rises in precipitation and evaporation at a global rate of 6-7%/K, global and regional climate models predict a muted response of the hydrologic cycle (2-3%/K). Quantitative estimation and prediction of precipitation still remain grand challenges in the hydrological and atmospheric sciences, both carrying huge uncertainties and thus preventing us from solving the previous conundrum. Observation-wise surface precipitation varies on spatial scales ranging from tens of meters to hundreds of kilometers, thus inhibiting the determination of spatio-temporal structures of precipitation fields from pointwise measurements only (e.g. rain gauges). Active and passive space-borne microwave measurements (precipitation radars, multi-wavelength radiometers) are considered to be suitable for estimating day and night-time precipitation rates and distributions on a planetary scale. Thanks to a satellite constellation concept the NASA-JAXA Global Precipitation Mission, due to launch early in 2014, promises to produce a significant step forward in improving coverage and reducing uncertainties in global precipitation products at a level sufficient to critically challenge numerical models. The presence of a first-ever-in-space dual frequency radar in the core satellite, with coverage up to 65 degrees latitude, will allow not only to know how much rain falls at the surface but also the detailed three-dimensional knowledge of rain, snow, and other forms of precipitation within the atmosphere above the surface and, with it, the links and the transfer of latent heat energy between the Earth's surface and atmosphere. This is an unprecedented opportunity in the mid-latitudes.
In our effort, by specifically focusing on UK and on the North Atlantic region, we will address two scientific objectives:
1) To quantify, understand, and potentially mitigate regime dependent biases that are present in today's passive microwave rainfall retrieval over ocean; 2) to critically assess the potential of Global Precipitation Mission-era passive microwave rainfall over mid-latitude coastal and rural areas. The UKMO radar network will be used as ground-reference for the satellite products; as a result, improvements on radar-based rainfall estimates over UK are expected as well. In addition, through improved measurements of precipitation globally, the Global Precipitation Mission will help advancing our understanding of Earth's water and energy cycle, improving forecasting of extreme events that cause natural hazards and disasters, and extending current capabilities in using accurate and timely information of precipitation to directly benefit society. This project will foster and help UK scientists and UK society in taking full advantage of such a unique opportunity.

Planned Impact

Life depends upon water. It impacts our lives and the natural environment through the every-day weather and the hydrological extremes of floods and drought. On a scientific level, water is one of the main drivers of the climate system, transferring and regulating energy within it. Despite the importance of water to us and the Earth system, our current knowledge of the occurrence and distribution of water across the planet and the mechanisms that drive the water cycle is very limited. Furthermore, our ability to accurately predict precipitation and its inherent spatio-temporal variability have not reached a mature level, partly due to the currently poor capability to accurately represent clouds and precipitation systems in cloud-resolving, regional and global models. The same applies to climate models and climate prediction. The GPM mission has a large potential towards advancing our knowledge of the global water cycle and its variability in a changing climate. It will provide, particularly over mid-latitude regions, improved measurements and predictions of precipitation that will lead to a greater understanding of water balances and processes of interest for water resources management, to a deeper insight in microphysics control on severe rainfall processes and to obvious consequential benefits for the UK society (e.g. improved capabilities in predicting flood and flash-flood producing storms).
Beneficiaries from this research will be (i) ESA and EUMETSAT, (ii) weather forecasting and climate prediction institutions like the UKMO, ECMWF, (iii) water management companies (especially in developing countries) , (iv) the International Panel on Climate Change, (v) UK government organizations and (vi) the general public.
The proposed research is extremely relevant and timely for upcoming ESA/EUMETSAT MetOp follow missions that will have three operational microwave instruments and will be part of the GMP constellation.
Weather forecasting and climate prediction institutions will benefit from an improved understanding of precipitation processes on all scales. GPM radiometer constellation will produce global estimates of precipitation within storms and our methodology will avoid or at least mitigate biases in such retrievals over the mid-latitudes. Our results will contribute to the final quality of the GPM mission products and, in the medium to long term, to improved micro-physical parameterizations and precipitation processes in weather and climate prediction models. Similarly the cross-calibration study between the GPM radar and the Met Office radars will contribute to improve precipitation products over UK with obvious benefit for organizations like DECC and DEFRA. Improved over-land precipitation products will be beneficial to water management companies, especially in developing countries where the ground-based measuring network is almost totally absent.
Climate change will have profound impact on the water cycle, the precipitation being one of the most unpredictable variables in a climate change scenario. While there is a general agreement on the fact that a warmer climate will also be wetter, there is no consensus on the amplitude of such an increase in precipitation and in the spatial patterns associated with it. The distribution of precipitation is likely to change as well, with frequency of heavy precipitation, polar precipitation and tropical cyclone intensity likely to increase, and precipitation over subtropical arid land regions likely to decrease (IPPC 2007 Report). Our research will improve understanding of precipitation events and their frequency of occurrence over the mid-latitudes and over UK, with great impact for government organizations and the wider public. The PI will act as GPM 'ambassador' in the UK and will convey the relevance of this mission both to the UK scientists and to the UK public with an articulated outreach program.


10 25 50
Description We have discovered that the interpretation of the GPM radar signals in deep convection and therefore in correspondence of extreme weather events become quite complicated because of a phenomenon called multiple scattering. This implies that we need to account for such an effect; otherwise, we can produce estimates of heavy rain that are heavily biased. This is utterly important because space-borne radars are the cornerstone of the global precipitation observing system and are used as 'calibrator' for other instruments (e.g. passive microwave radiometers). We have now validated the GPM DPR radar and radar/radiometer products over UK and adjacent coastal regions by using the Met Office Radarnet. The results show that the Combined and DPR products underestimate rain rates with respect to Radarnet by 21% and 31% respectively, when considering 25 km resolution data taken within a 75 km vicinity of a ground-based radar. Underestimation appear to be a consequence of issues with the clutter free bin bottom determination in the DPR and combined algorithms. We are currently investigating the possibility of improving the clutter detection algorithm.
Exploitation Route Precipitation is expected to increase with global warming but we still do not know what is the precipitation sensitivity and how the distribution of precipitation will change (e.g. will there be more intense precipitation?). Our findings will help improve the precipitation record derived from global observing systems (specifically the products derived from the GPM core satellite), particularly in relation to extreme weather events.
Sectors Aerospace, Defence and Marine,Agriculture, Food and Drink,Environment

Description The project is contributing to improve the Level2 NASA GPM DPR product via introducing a flagging for profiles likely contaminated by multiple scattering and non uniform beam filling and by using an ad-hoc retrieval for such profiles. Also the project has validated GPM products over UK via the UK MetOffcie radars
First Year Of Impact 2017
Sector Environment
Impact Types Cultural

Description CENTA DTP Studentship
Amount £60,000 (GBP)
Organisation Natural Environment Research Council 
Sector Public
Country United Kingdom
Start 10/2017 
End 02/2021
Description ESA ITT Multifrequency radar instrument study
Amount € 300,000 (EUR)
Organisation ESA - ESTEC 
Sector Public
Country Netherlands
Start 04/2017 
End 10/2018
Description Multi-frequency radar instrument study
Amount € 300,000 (EUR)
Organisation ESA - ESTEC 
Sector Public
Country Netherlands
Start 05/2017 
End 12/2018
Title Best proxies for hail detection with remote sensing from space 
Description By comparison with ground-based observation, the best GPM proxy for hail detection is the mean radar reflectivity above the freezing level (with slightly better performances when using dual-frequency) 
Type Of Material Improvements to research infrastructure 
Provided To Others? No  
Impact This research tool will allow to produce a database of world hail occurence 
Title Optimal Estimation retrieval for multi-wavelength radar/radiometer 
Description This is an optimal estimation methodology to retrieve profile of hydrometeors from radar reflectivity profiles derived from space-borne and airborne radars 
Type Of Material Improvements to research infrastructure 
Year Produced 2014 
Provided To Others? Yes  
Impact This retrieval method should be integrated for deriving Level2 NASA-GPM product and it is currently applied to measurements acquired by the NASA-DC8 aircraft 
Title Spatio-temporal variability of drop size distribution 
Description This database provides the temporal variability of drop size distributions profiles over ARM sites equipped with dual frequency Doppler radars 
Type Of Material Database/Collection of data 
Year Produced 2016 
Provided To Others? Yes  
Impact The characterization of the spatio-temporal variability of the drop size distribution will help in refining satellite rainfall retrievals. This database has already been used to validate an assimilation method for the study of drop size distribution (Mercier, F., Chazottes, A., Barthès, L., and Mallet, C.: 4-D-VAR assimilation of disdrometer data and radar spectral reflectivities for raindrop size distribution and vertical wind retrievals, Atmos. Meas. Tech., 9, 3145-3163, doi:10.5194/amt-9-3145-2016, 2016) 
Title World map of hail occurence 
Description Global map of hail frequency from GPM spaceborne dual-frequency radar 
Type Of Material Database/Collection of data 
Provided To Others? No  
Impact Such database can help insurance companies to assess the risks related to hail damage. 
Description Clermont University (France) 
Organisation Blaise Pascal University
Department Laboratory of Physical Meteorology
Country France 
Sector Academic/University 
PI Contribution We provided retrievals of the vertical variability of rain microphysical parameters for a squall line observed over Oklahoma.
Collaborator Contribution They ran WRF simulations of the case study and performed sensitivity studies on the parametrization of rain microphysics in order to explain discrepancies with observations.
Impact The intercomparison of rain properties shows that the most used microphysical schemes of the WRF model can not reproduce observations. A paper is in preparation.
Start Year 2016
Description NASA Goddard 
Organisation National Aeronautics and Space Administration (NASA)
Country United States 
Sector Public 
PI Contribution We are currently analysing the multi-frequency airborne Doppler radar data for two deep convective systems occurred during the HYPHEx campaign in 2014. A paper is almost ready for submission
Collaborator Contribution Dr. Gerry Heymsfield is providing airborne Doppler radar data for different GPM GV campaigns
Impact Paper currently under submission How deep and what can a multi-wavelength suite of microwave instruments see in deep convective cores? by A. Battaglia, F. Tridon, K. Mroz, S. Tanelli, Tim Lang, Gerry Heymsfield Lin Tian
Start Year 2014
Description NASA JPL 
Organisation National Aeronautics and Space Administration (NASA)
Department Jet Propulsion Laboratory
Country United States 
Sector Public 
PI Contribution Dr Battaglia is international collaborator in the 'Advanced datasets to diagnose higher-order features embedded in expected GPM measurements and their impact on retrieval algorithms' project part of the NASA ROSES Precipitation Science Research Program and led by Dr S. Tanelli, NASA-JPL. Our research team is developing retrieval algorithm for rain and snow and it is applying them to the airborne datasets provided by JPL.
Collaborator Contribution Dr Tanelli, PI of the APR-3 radar, is providing datastes collected during GPM field campaigns and collaborating with us on the development of retrieval algorithms.
Impact Several papers with co-authorships of S. Tanelli K. Mroz, Battaglia, A., T. Lang, D. Cecil, S. Tanelli and F.Tridon, Hail detection algorithm for the GPM core satellite sensors, 2017, conditionally accepted in JAMC. Burns, D., P. Kollias, A. Tatarevic, A. Battaglia, S. Tanelli, The Performance of the EarthCARE Cloud Profiling Radar in Marine Stratiform Clouds, 2016, Journal of Geophysical Research: Atmospheres, 10.1002/2016JD025090. Battaglia, A., K. Mroz, T. Lang, F. Tridon, S. Tanelli, L. Tian and G. Heymsfield, Using a multi-wavelength suite of microwave instruments to investigate the microphysical structure of deep convective cores, Journal of Geophysical Research: Atmospheres, 2016, 10.1002/2016JD025269. Battaglia, A., K., S. Tanelli, F. Tridon, P.E. Kirstetter, Multiple-scattering-induced "ghost echoes" in GPM-DPR observations of a tornadic supercell, DOI:
Start Year 2014
Description NASA Marshall 
Organisation National Aeronautics and Space Administration (NASA)
Department Marshall Space Flight Center
Country United States 
Sector Public 
PI Contribution We have used data from AMPR radiometer and used to retrieve the microphysics in deep convective cores
Collaborator Contribution They have helped in the interpretation of brightness temperatures and they have provided data of collocated ground-based polarimetric radars
Impact K. Mroz, Battaglia, A., T. Lang, D. Cecil, S. Tanelli and F.Tridon, Hail detection algorithm for the GPM core satellite sensors, 2017, conditionally accepted in JAMC. Battaglia, A., K. Mroz, T. Lang, F. Tridon, S. Tanelli, L. Tian and G. Heymsfield, Using a multi-wavelength suite of microwave instruments to investigate the microphysical structure of deep convective cores, Journal of Geophysical Research: Atmospheres, 2016, 10.1002/2016JD025269
Start Year 2015
Description StonyBrook and ARM collaborators 
Organisation Stony Brook University
Department School of Marine and Atmospheric Sciences
Country United States 
Sector Academic/University 
PI Contribution We have been involved in analysing ARM datasets of multifrequency Doppler observations
Collaborator Contribution They have provided expertise in the quality control and calibration of radar data and their own retrieval
Impact Tridon F. and Battaglia, A., P. Kollias and E. Luke, Rain retrieval from dual-frequency radar Doppler spectra: validation and potential for a midlatitude precipitating case study, 2017, QJRMS, doi:10.1002/qj.3010 Kneifel, S., Kollias, P., Battaglia, A., Leinonen, J., Maahn, M., Kalesse, H., Tridon, F., First observations of triple-frequency radar Doppler spectra in snowfall: Interpretation and applications, Geophys. Res. Lett., 2016, 43, doi: 10.1002/2015GL067618. 49. F Tridon, A Battaglia, Dual-frequency radar Doppler spectral retrieval of rain drop size distributions and entangled dynamics variables, Journal of Geophysical Research: Atmospheres, 10.1002/2014JD023023
Start Year 2014
Description collaboration with NASA GISS 
Organisation National Aeronautics and Space Administration (NASA)
Department NASA Goddard Institute for Space Studies
Country United States 
Sector Public 
PI Contribution We have been working on retrievals of stratiform rain during the OLYMPEX field campaign. We are providing ice microphysical properties as derived from multi frequency radar observations, which are useful for 2-moment microphysics scheme.
Collaborator Contribution The group led by Ann Fridlind is providing GCM and LES model outputs to be compared with our measurements and tries to improve cloud parameterizations.
Impact Successful proposal to US-DoE on Antarctic clouds
Start Year 2017