Atmospheric polarimetric effects on GNSS radio occultations:  the ROHP-PAZ field campaign

Padullés, Ramon; Cardellach, Estel; Juárez, Manuel de la Torre; Tomás, S.; Turk, F. Joseph; Oliveras, S.; Ao, C. O.; Rius, A.

doi:10.5194/acp-16-635-2016

Cited by 16 publications

(25 citation statements)

References 28 publications

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“…The main payload of PAZ is an X-band synthetic aperture radar (SAR), decoupled from and not used by the ROHP-PAZ experiment. The GNSS PRO technique was confirmed further in an experimental field campaign from a mountain top (Padullés et al, 2016a). A preliminary data-processing technique to resolve precipitation structures from GNSS PRO was introduced by Padullés et al (2016b), but they showed that it would work only under certain limited conditions.…”

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confidence: 97%

“…Since precipitation-sized hydrometeors are typically aspherically shaped, the differential phase of the received signal is modified during tangential propagation through clouds associated with heavy precipitation. In the case of PRO, propagation through liquid precipitation or large crystalline ice (Vivekanandan et al, 1994) will induce a cross-polarized component (Padullés et al, 2016a). The measurement of differential propagation phase shifts has been studied in detail by the ground-based weather radar community (Bringi et al, 1990) and is now an integral part of the USA nationwide Next-Generation Radar (NEXRAD) radar system (e.g.…”

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confidence: 99%

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Probability of intense precipitation from polarimetric GNSS radio occultation observations

Cardellach

Padullés

Tomás

et al. 2017

Quart J Royal Meteoro Soc

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There is currently a gap in satellite observations of the moisture structure during heavy precipitation conditions, since infrared and microwave sounders cannot sense water-vapour structure near the surface in the presence of intense precipitation. Conversely, Global Navigation Satellite System (GNSS) radio occultations (RO) can profile the moisture structure with high precision and vertical resolution, but cannot indicate the presence of precipitation directly. Polarimetric RO (PRO) measurements have been proposed as a method to characterize heavy rain in GNSS RO, by measuring the polarimetric differential phase delay induced by large size hydrometeors. Previous studies have shown that the PRO polarimetric phase shift is sensitive to the path-integrated rain rate under intense precipitation scenarios, but there is no current method to invert PRO measurements into quantitative estimates of the path-averaged rain rate. In this manuscript, a probabilistic inversion approach to the GNSS PRO observables is proposed, where the GPM precipitation products are used for the construction of an a priori look-up table (LUT) database. The performance of the LUTs is assessed for use in the inversion of satellite-based GNSS PRO observations, based on synthetically generated PRO data of actual events, which correspond to co-locations between GNSS RO profiles and the TRMM observations. The synthetic data include end-to-end propagation effects of the polarimetric observables and a simple separation algorithm to isolate the hydrometeor component of the observation. The assessment results in agreement better than ±1 mm h −1 between the reference LUT and the actual rain statistics of the synthetic data, proving the suitability of the GPMbased probabilistic inversion tool. These findings indicate that the GNSS PRO products are capable of extending the current GNSS RO ones by associating indications of rainrate probabilities at different altitudes, at ∼250 m vertical resolution and under intense precipitation scenarios with the standard vertical thermodynamic profiles.

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confidence: 97%

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confidence: 99%

Probability of intense precipitation from polarimetric GNSS radio occultation observations

Cardellach

Padullés

Tomás

et al. 2017

Quart J Royal Meteoro Soc

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“…The vertical information in RO additionally detects the vertical changes in stability to convection and discriminates what atmospheric layers control rain. RO profiles can thus improve our understanding of global processes internal to precipitating clouds when they are collocated with precipitation information, as done here with TRMM, or in the future with Polarimetric RO (Cardellach et al, ; Padullés et al, ) as planned with the PAZ satellite, or with cloud information as given by CloudSat.…”

Section: Discussionmentioning

confidence: 99%

Signatures of Heavy Precipitation on the Thermodynamics of Clouds Seen From Satellite: Changes Observed in Temperature Lapse Rates and Missed by Weather Analyses

et al. 2018

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Analyses of the thermodynamics of precipitating clouds are mostly based on localized in situ campaigns or, more globally, weather analyses and reanalyses. This work presents a comparison of weather analyses to satellite observations and a radiometeorological method that shows how precipitating layers inside clouds coincide with weather analyses underestimates of the amount of water vapor. The thermodynamic information from inside precipitating clouds is extracted using observed radio occultation (RO) refractivity profiles without requiring weather analysis input, thus reducing analysis-induced biases. The radiometeorological method is described by first identifying the differences between adiabatically dry, mixing-ratio conserving, and saturated pseudoadiabatic refractivity profiles. These reference profiles are then compared to observed RO refractivity profiles within precipitating and nonprecipitating clouds to infer changes in their height-dependent thermodynamic states and in stability to convection. Precipitation is found to start below layers close to pseudoadiabatic and precipitation layers coincide with changes into conditional stability against convection. A statistical comparison between observed profiles and the gradients predicted for a saturated pseudoadiabatic profile is made and finds that on the global average, precipitation separates clouds from the Clausius-Clapeyron law and profiles are close to a saturated pseudoadiabat. The results (a) help constrain the physical processes associated to precipitation inside clouds and (b) validate the potential of graphical RO techniques to analyze observations without ancillary temperature data from weather analyses. Plain Language SummaryPredicting how precipitation responds to changes in atmospheric thermal profiles remains a challenge identified by the Intergovernmental Panel on Climate Change. Solving this challenge requires comparing models with the observed thermodynamics of precipitating clouds. Only radio occultation (RO) can constraint globally the thermodynamics inside clouds with high vertical resolution. Infrared and microwave can measure the thermodynamics outside and only partially clouds, and radar instruments that measure inside clouds do not provide thermodynamic information.This paper develops a method to use RO for distinguishing the thermodynamics inside precipitating versus nonprecipitating clouds. The identification of rain is made using coincidences of RO soundings with Tropical Rainfall Measuring Mission and CloudSat observations. Using the method, we show that globally, (1) the European Center for Medium-Range Weather Forecast ERA Interim reanalysis and the Global Forecast System weather analysis have a global bias in precipitating clouds caused by misrepresentation of the thermodynamics inside clouds; (2) the nature of the bias is associated to a misrepresentation of the lapse rates by the analyses; (3) there are changes in stability to moist convection associated to the height where precipitation originates, and (4) the transition ...

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“…The study performed in Cardellach et al [2015] demonstrated not only that heavy rain events could be detected, but also that an approximated vertical structure of the rain cell could be retrieved. The concept has been tested in a field campaign [Padullés et al, 2016] with promising results in views to the spaceborne mission. One of the limitations of this new concept is the ambiguity between the effect of the rain rate and the effect of the rain cell size, due to the along-path integrated nature of the RO observations.…”

Section: Introductionmentioning

confidence: 99%

Untangling rain structure from polarimetric GNSS Radio Occultation observables: a 2D tomographic approach

Padullés

Cardellach

Rius

2016

European Journal of Remote Sensing

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A new rain measurement concept will be tested aboard the Low Earth Orbiter (LEO) PAZ, (launch planned for 2016). It aims to detect and quantify intense rain using the polarimetric phase-shift induced by rain droplets along GNSS radio occultation's rays. Due to the integral nature of the measurement, rain intensity and extension are difficult to untangle. The work presented here applies tomographic techniques to reconstruct the precipitation structure from the integrated measurement. The technique shows the capability of retrieving simple structures using only the information self contained in the radio occultation observables, while for more complex structures external information would be needed in order to refine the retrievals.

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Atmospheric polarimetric effects on GNSS radio occultations: the ROHP-PAZ field campaign

Cited by 16 publications

References 28 publications

Probability of intense precipitation from polarimetric GNSS radio occultation observations

Probability of intense precipitation from polarimetric GNSS radio occultation observations

Signatures of Heavy Precipitation on the Thermodynamics of Clouds Seen From Satellite: Changes Observed in Temperature Lapse Rates and Missed by Weather Analyses

Untangling rain structure from polarimetric GNSS Radio Occultation observables: a 2D tomographic approach

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