concordiasi gps radio occultation€¦ · alexandria johnson, brian murphy – purdue graduate...

Concordiasi GPS Radio Occultation Proof-of-concept Atmospheric Profiling with GPS Radio Occultation from Stratospheric Balloons in the Antarctic

Jennifer Haase Purdue University Earth & Atmospheric Sciences

Jayson Maldonado – UPRM Undergraduate student Alexandria Johnson, Brian Murphy – Purdue Graduate students

Phil Wyss- Purdue AMY Chemistry Facility Philippe Cocquerez, Marc Minois CNES –French Space Agency

Florence Rabier, Vincent Guidard – Météofrance Albert Hertzog, LMD Paris

Science Objectives

• Understand the flight dynamics of the balloon platform

• Observe gravity waves for the parameterization of momentum flux into the stratosphere

• Use the radio occultation profiles for verification to improve the assimilation of space-borne atmospheric sounders, in particular IASI on board MetOp

Radio Occultation (ROC) System

ROC

CNES Gondola

Location of GPS antenna

Hertzog, Rabier et al, 2011, SPARC workshop

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Hertzog, Rabier et al, 2011, SPARC workshop

GPS precise positioning

• 30 second sampling routinely

• 15 second sampling for one traverse of the Antarctic peninsula

• GPS observations allow separation of pressure and height variations in gravity wave spectra

Flight dynamics

• Accuracy of position determined using two independent antenna/receivers on PSC18

35 cm east and north difference limits corresponds to separation of antennas

East difference

North difference

Height difference

50 cm height difference give absolute accuracy of precise positioning height estimates

Flight Dynamics

• Rotation rate of ~75o to 300o per hour

Background

GPS radio occultation will be used to obtain atmospheric profiles of refractivity for verification in IASI assimilation studies and for IASI retrievals

Radio signals pass through the atmosphere from GPS satellite to GPS receiver on balloon

As it travels, the signal encounters atmospheric layers of varying density

The density changes cause the signal to refract and delay slightly

A Doppler shift is associated with the overall delay seen in the signal and can be converted into an atmospheric refractivity value at a geometrically determined tangent point to the Earth

r(tan)‏

TOA

GPS Receiver

GPS Satellite

Zero elevation

Negative elevation (occultation)

GPS satellite at positive elevation

rearth

rballoon

rtangent

Atmospheric refractivity Is retrieved at the

indicated tangent points

ratmo

Stratospheric balloon

The delay in the GPS signal increases as the line of sight between the balloon and satellite moves lower in the atmosphere

Altitud

e (

km

)

Ground level

Refractivity (N units)

Troposphere

Stratosphere

delay = N dsraypathò

N = 77.6 ´10-2 P

T+ 70.4 ´10-2 e

T+ 3.739 ´103 e

T2

Campaign planning Simulated occultations using 2005

VORCORE 110 day trajectory

An average of 115 occultations

per day, 58 of which are setting

Large tangent drifts

Only possible to transmit

< 10 per day because of

IRIDIUM data limitations

PSC18 and PSC19 flights

• Total of 711 occultations with duration greater than 7 minutes of continuous data below the horizon

• 687 total dropsondes on 13 balloons

PSC18 and PSC19

o PSC18 o PSC19 o dropsondes

Comparison Dropsonde and ARPEGE profiles

No precise reference for geometric height for dropsonde profile

Dropsonde – ARPEGE Refractivity

Excess phase and Doppler for PRN25 day 2010 297

Rising Occultations

• Recorded rising occultations as well as setting with comparable duration and frequency

Penetration depth of occultations

GEOS-5 Observation Impacts for Concordiasi Average for All Drop Cases − 60°S-90°S Observations

Total Impact Impact Per Observation

Observation Count % Beneficial Observations

R Gelaro 2011 Thorpex DAO Working Group

COSMIC distribution of profiles

o PSC18 o PSC19 o COSMIC RO

6111 COSMIC profiles in 54 days Good accuracy at UT/LS

711 ROC profiles in 54 days Without $$ constraint 115 profiles/day * 54 days = 6210 profiles for each balloon Reduced accuracy at UT/LS

Conclusions

• Successful mission – exceeded expectations for a prototype mission

• Retrieved 6-9 profiles per day for each balloon as expected with equally good quality for rising and setting occultations

• During the two balloon flights:

• a combined total of 107 days,

• more than 700 occultations were recorded (number limited by the data transmission rates)

• More than 32% of the profiles (227) descended within 4km of surface

• Very good outlook for contributing to the goal of improving atmospheric models in the Antarctic and improving the description of gravity wave momentum flux

Acknowledgements

• NSF Grants 0814290 and ANT-1043676 that provided GPS ROC development and campaign support, and University of Puerto Rico of Mayaguez for summer internship funding

• James Zimmerman and the AMY Chemistry facility for ROC development

• Olivier Gallien, Jean-Marc Nicot and the team at CNES for assistance with the GPS ROC integration into the stratospheric balloons

• Concordiasi was built by an international scientific group and is currently supported by the following agencies: Météo-France, CNES, CNRS/INSU, NSF, NCAR, University of Wyoming, Purdue University, University of Colorado, the Alfred Wegener Institute, the Met Office and ECMWF. Concordiasi also benefits from logistic or financial support of the operational polar agencies IPEV, PNRA, USAP and BAS, and from BSRN measurements at Concordia. Concordiasi is part of the THORPEX-IPY cluster within the International Polar Year effort. Detailed information on Concordiasi is available on the web site “http://www.cnrm.meteo.fr/concordiasi/”.

• The driftsonde data for this project were quality controlled and are maintained by the Earth Observing Laboratory at the National Center for Atmospheric Research (NCAR). NCAR is sponsored by the National Science Foundation (NSF). Reference: J. Wang, K. Young, T. Hock, N. Potts, and C. Martin, 2011: Concordiasi 2010 quality controlled driftsonde data set. Available at http:/www.eol.ucar.edu/projects/concordiasi

Elevation angle and Continuity Typical configuration – no data sent between 0o and 20o

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PSC18 Hour of day 2010-10-11 PSC19 Hour of day 2010-10-24

Special observing period 5 sec continuously

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Challenges unique to Antarctica

• Temperatures are not cold enough at the surface over the Antarctic plateau

• Temperatures are not warm enough over sea ice

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Challenges unique to Antarctica

• IASI retrievals have trouble reproducing steep stable boundary layer from the first guess

• These problems interfere with cloud detection algorithms which limit the height range of IASI radiances that can be assimilated


Simulated occultations using 2005 VORCORE 110 day trajectory

An average of 115 occultations

per day, 58 of which are setting

Large tangent drifts

Only possible to transmit ~13 per day because of IRIDIUM data limitations

Campaign planning

concordiasi gps radio occultation€¦ · alexandria johnson, brian murphy – purdue graduate...

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