Monitoring atmospheric severeconvection from 60°S to 60°N using

passive microwave radiometry

JF Rysman, C Claud, JP Chaboureau,J Delanoe, BM Funatsujfrysman@lmd.polytechnique.fr

Context/Motivation

• Atmospheric convection is a quasi globalphenomenon which is often associated withsevere weather

• Need for comprehensive and homogeneousmonitoring of this phenomenon

Context/Motivation

• Atmospheric convection is a quasi globalphenomenon which is often associated withsevere weather

• Need for comprehensive and homogeneousmonitoring of this phenomenon

• Can be achieved using space borne instruments (radar, infraredsensors, microwave radiometers)

• Microwave instruments are sensitive to hydrometeors and thus canbe used to detect convection

=> Passive space-borne microwave sounders (AMSU-B, MHS, ATMS)

• AMSU-B is a space borne passive microwave radiometer

• 5 channels: 2 window channels and 3channels around the water vapourabsorption line (183 GHz)

• Swath-width of 2000 km and nadirresolution of 16 km

• Viewing angle from 0.6° to 60°

• MHS and ATMS are very similar (same frequencies) to AMSU-B

Advanced Microwave Sounding Unit(AMSU-B)

Temporal coverage

• From 2002 onwards atleast 3 satellites fly conjointly

• Good temporal coverage with 3-4 hourresolution, crossing hours depend on the year/orbite

Crossing time of the equator

How to detect convection with passive microwave sounders ?

• Using these characteristics,Hong et al. 2005, JGR developped 2 criteriaof severe convection named deep convectionand convective overshooting

1/ Water vapour channels probe in mid-atmosphere

2/ Frozen hydrometeors scatter Earthradiation at microwave frequencies

=> It is possible to detect heavy iceloading in mid-atmosphere signature ofconvection

Weighting function ofAMSU-B

Method

Windowschannels

Water vapourchannels

However these criteria have been developed for the tropical regions and donot inform on the microphysics characteristics of the detected events

Method

Objective: evaluate and characterise these criteria from 60°S/60°N

Method: Thousand of collocations between MHS and Cloudsat/Calipsofrom 2006 to present

27 October 2012

Heavy rain in Albania/Greece(>200 mm/36h)

DC and COV detected by MHS

High reflectivity measured by Cloudsat

Tropopause

COV

DC

Evaluation and characterisation of Deep Convection andConvective Overshooting criteria

1/ We used the Cloudsat Level 2 Cloud Scenario Classification product (Wang et al. 2007) to evaluate the DC & COV criteria

• DC valid when associated with Deep Convective Clouds

• COV valid when associated with Deep Convective CloudsAND ice associated with COV reaches the Tropopause

MethodEvaluation and characterisation of Deep Convection andConvective Overshooting criteria

1/ We used the Cloudsat Level 2 Cloud Scenario Classification product (Wang et al. 2007) to evaluate the DC & COV criteria

• DC valid when associated with Deep Convective Clouds

• COV valid when associated with Deep Convective CloudsAND ice associated with COV reaches the Tropopause

2/ We used the DARDAR-Cloud product (Delanoë et al. 2010) tocharacterize the DC and COV criteria

• DARDAR-Cloud retrieves the ice microphysics combining Cloudsat andCALIPSO measurements

MethodEvaluation and characterisation of Deep Convection andConvective Overshooting criteria

ResultsValidity of Deep Convection/Convective Overshooting criteria

• Both criteria are associated with Deep Convective Clouds > 90%of time

• COV effectively reaches the Tropopause 51% of time

• Both criteria are associated with Deep Convective Clouds > 90%of time

• COV effectively reaches the Tropopause 51% of time

• Problem in frozen soil regions (e.g., Siberia) and mountain range

False positive as a function of monthRysman et al., in reviewIEEE Geosci. Remote Sens. Lett.

ResultsValidity of Deep Convection/Convective Overshooting criteria

ResultsMicrophysics of Deep Convection and Convective Overshooting

• Effective radius quite similarfor both diagnostics

• ER decreases rapidly withaltitude

• Ice reaches lower altitude forDC

• Maximum of IWC is lower forCOV

Rysman et al., in reviewIEEE Geosci. Remote Sens. Lett.

ResultsToward a climatology of Deep Convection and Convective Overshooting

Data checking, some problems are better documented than others ...

Average number of DC occurrence

ResultsToward a climatology of Deep Convection and Convective Overshooting

Data checking, some problems are better documented than others ...

Brightness temperature of windows channel 1 of AMSU-B

Average number of DC occurrence

ResultsToward a climatology of Deep Convection and Convective Overshooting

Data checking, some problems are better documented than others ...

ResultsClimatology of Deep Convection and Convective Overshooting

• Range: 60°S/60°N• Daily resolution• 0.2°x 0.2° resolution

DC occurrence between 1999 and 2015

• Range: 60°S/60°N• Daily resolution• 0.2°x 0.2° resolution

January-March 2015 June-August 2015

Number of DC occurrence

ResultsClimatology of Deep Convection and Convective Overshooting

ResultsClimatology of Deep Convection and Convective Overshooting

Number of daily DC occurrence

Related studies from our group

• Characterization of convection in theMediterranean during the 2012Autumn (Rysman et al. 2016, QJRMS)

• Evaluation of rainfall andconvection from WRF model usingMHS/AMSU-B measurements(Rysman et al. 2016, Clim Dyn)

• Relationship between DC andMediterranean hurricanes(Claud et al. 2010, NHESS)

Conclusion

• We use spaceborne passive microwave instruments to detectconvection

• We validated and characterized the convective events detectedby microwave sounders

=> Passive microwave radiometers can be used to monitor convectionfrom 60°S/60°N except in mountainous and frozen soil regions

• We are building of quasi-global climatology of convective events

Thank you for your attention