Global Assimilative Ionospheric Modeling and COSMIC-2 · Global Assimilative Ionospheric Modeling...

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Global Assimilative Ionospheric Modeling and COSMIC-2 Clayton Coker Naval Research Laboratory, Washington, DC, [email protected] Xiaoqing Pi, Atilla Komjathy and Anthony Mannucci Jet Propulsion Laboratory, Pasadena, CA

Transcript of Global Assimilative Ionospheric Modeling and COSMIC-2 · Global Assimilative Ionospheric Modeling...

Page 1: Global Assimilative Ionospheric Modeling and COSMIC-2 · Global Assimilative Ionospheric Modeling and COSMIC-2 ... With the launch of the COSMIC constellation of GPS radio ... high

Global Assimilative Ionospheric Modeling and

COSMIC-2

Clayton Coker

Naval Research Laboratory, Washington, DC, [email protected]

Xiaoqing Pi, Atilla Komjathy and Anthony Mannucci

Jet Propulsion Laboratory, Pasadena, CA

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With the launch of the COSMIC constellation of GPS radio occultation sensors in

2006, research began on assimilating data from multiple GPS radio occultations into

global assimilative ionospheric models. These space-based observations provide the

advantage of global coverage compared to ground-based GPS stations but suffer

from low horizontal resolution. Plans are on the table to deploy even larger

constellations of GPS radio occultation sensors. Will these larger constellations

with double or quadruple the number of observations of the space environment drive

the assimilative models to the next level of performance in resolution and

accuracy? Early in the COSMIC mission multiple spacecraft were in the same orbit,

providing a high density of radio occultation data near the local time of that orbit – a

condition analogous to proposed COSMIC-2 constellations with multiple sensors

in each orbit. The resulting high density radio occultation data are ingested into

global assimilative models, and the performance of the models are validated using

high resolution UV photometer data from COSMIC. The Tiny Ionospheric

Photometer (TIP) on COSMIC is a compact, nadir directed, narrow-band, ultraviolet

photometer operating at the 135.6 nm wavelength and measuring the horizontal

structure of the ionosphere with 15-30 km resolution. Comparisons with TIP data

reveals the horizontal performance of these models and demonstrates the

improvement obtained from ingesting the high density radio occultation data.

Abstract

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Early in the COSMIC mission, three SVs in the same orbit plane.

Provides higher density coverage near the orbit (or local time).

Provides a glimpse into future data densities provided by COSMIC-2.

COSMIC-2 with 12 SVs will provide a factor of 2 to 4 more RO samples.

What is the impact of COSMIC-2 on assimilative ionospheric models?

Rayleighs

Radio Occultations from three COSMIC SVs in 2100LT orbit

Constellation with 3x Data Density of COSMIC

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Climatology Background Model for 2100LT

Rayleighs

Evaluation of Impact of Future Missions

What is the impact of COSMIC-2 data densities on

assimilative ionospheric models?

Assimilation of high density RO data and all

available ground GPS data into GAIMUSC – focus

on specification near the orbit.

Validation using Tiny Ionospheric Photometer

Rayleighs

Radio Occultations from three COSMIC SVs in 2100LT orbit

Tiny Ionosphere Photometer Data

GAIM–TIP RMS 1.2 R Climatology–TIP RMS 2.5 R

GAIM GAIM Ionospheric Specification for 2100LT on 14 Sep 2006

Rayleighs

Ground GPS

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TIP

GAIM USC Climate

Rayleighs

GAIM USC Ground GPS

Rayleighs

GAIM USC Ground + RO

Rayleighs

GAIMUSC Climate–TIP RMS 2.5 R

GAIMUSC Ground–TIP RMS 1.4 R

GAIMUSC Ground+RO–TIP RMS 1.2 R

Impact of Multiple RO Sensors in Each Orbit to

Assimilative Modeling

Ground GPS (all available stations) provides a

reasonable specification of global ionosphere –

some areas fall back to climatology.

Adding RO data improves performance.

Improves global coverage.

Better definition of anomaly trough

Artifacts due to ambiguity in RO data in the

presence of ionospheric gradients (equatorial

ionospheric anomaly).

45%

15%

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TIP is an ultraviolet photometer measuring 135.6 nm emissions from recombination of oxygen ions and electrons

– intensity is integral of density-squared along the line of sight, similar to TEC.

TIP looks downward from the COSMIC spacecraft and maps the equatorial ionization anomaly with high

resolution along the path of the satellites.

Longitudinal variability is driven by zonal winds influenced by tidal modes.

Variability in anomaly crest intensity is 1-20 Rayleighs (5-25 TECU) in longitude.

Variability in crest separation ranges from 30° to 12° with no anomaly at some longitudes.

TIP Observations of Low Latitude Ionosphere

Magnetic Latitude

Ra

yle

igh

s

14 Sep 2006 21LT

10 TECU

15 TECU

20 TECU

5 TECU

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Climatology overestimates 21LT ionosphere near solar minimum.

Adding Ground GPS data drives output closer to truth, but not all longitudes

covered.

Adding space-based RO data provides global coverage, drives output towards

correct global average.

Climatology

Ground GPS

Ground+RO

TIP

Magnetic Latitude

135.6

-nm

Rad

iance

- R

ayle

ighs

10 TECU

15 TECU

20 TECU

5 TECU

Comparison of GAIMUSC Runs with TIP Data

Global Average Ionosphere @ 21LT

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Climatology does not improve ionospheric correction error at some latitudes – trough

and transitions between mid and low latitudes.

Adding Ground GPS data drives the error down at low latitudes, but trough and

transitions need improvement.

Adding space-based RO data drives the error down at trough and southern transition,

but does not improve results at anomaly crests – need better gradient info.

RMS Error of GAIMUSC Runs

Global RMS Error @ 21LT

Climatology – TIP Ground GPS – TIP

Ground+RO – TIP

TIP

Magnetic Latitude

RM

S E

rror

– R

ayle

ighs

TIP 135.6-nm

Radiances

10 TECU

15 TECU

20 TECU

5 TECU

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Climatology

Ground GPS

Ground+RO

TIP data RO data

Magnetic Latitude

135.6

-nm

Rad

iance

- R

ayle

ighs

10 TECU

15 TECU

20 TECU

5 TECU

S American Sector

Comparison of GAIMUSC Runs with TIP Data

Example where ground

GPS is abundant.

45-deg

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Climatology

Ground GPS

Ground + RO

Magnetic Latitude

Alt

itude

45-deg

Density

1e5/cm3

8

5

4

1

0

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Climatology

Ground GPS

Ground+RO

TIP data RO data

Magnetic Latitude

135.6

-nm

Rad

iance

- R

ayle

ighs

10 TECU

15 TECU

20 TECU

5 TECU

Hawaiian Sector

Comparison of GAIMUSC Runs with TIP Data

Example where ground

GPS is sparse and

anomaly is symmetric.

45-deg

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Climatology

Ground GPS

Ground + RO

Magnetic Latitude

Alt

itude

45-deg

Density

1e5/cm3

8

5

4

1

0

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Climatology

Ground GPS

Ground+RO

TIP data RO data

Magnetic Latitude

135.6

-nm

Rad

iance

- R

ayle

ighs

10 TECU

15 TECU

20 TECU

5 TECU

Kwajalein Sector

Comparison of GAIMUSC Runs with TIP Data

Example where ground GPS is sparse in the

Southern Hemisphere and nonexistent in

Northern Hemisphere.

45-deg

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Climatology

Ground GPS

Ground + RO

Magnetic Latitude

Alt

itude

45-deg

Density

1e5/cm3

8

5

4

1

0

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Indian Sector

Comparison of GAIMUSC Runs with TIP Data

Climatology

Ground GPS

Ground+RO

TIP data RO data

Magnetic Latitude

135.6

-nm

Rad

iance

- R

ayle

ighs

10 TECU

15 TECU

20 TECU

5 TECU

Example where ground GPS

coverage is reasonable but anomaly

is collapsed – low densities.

45-deg

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Climatology

Ground GPS

Ground + RO

Magnetic Latitude

Alt

itude

45-deg

Density

1e5/cm3

8

5

4

1

0

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Climatology

Ground GPS

Ground+RO

TIP data RO data

Magnetic Latitude

135.6

-nm

Rad

iance

- R

ayle

ighs

10 TECU

15 TECU

20 TECU

5 TECU

Atlantic Sector

Comparison of GAIMUSC Runs with TIP Data

Example where ground GPS is

sparse and anomaly is

collapsed – low densities.

45-deg

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Climatology

Ground GPS

Ground + RO

Magnetic Latitude

Alt

itude

45-deg

Density

1e5/cm3

8

5

4

1

0

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Conclusions

•  Early COSMIC rollout period provides coverage similar to proposed COSMIC-2.

–  Triple the number of radio occultations near the orbit plane.

•  When assimilating data similar to COSMIC-2, the ionospheric RMS error was

reduced by 15% compared with the model run using ground GPS data only.

•  Improvement to assimilative ionospheric modeling is clearly observed in the trough

of the equatorial anomaly.

•  No improvement is observed at the crests of the anomaly.

– When horizontal constraints are limited (sparse ground GPS stations), the model often miss

positions and/or broadens the anomaly crest.

•  COSMIC-2 does not provide sufficient density of data samples to produce high

resolution specification of the post-sunset ionospheric anomaly.

–  Need secondary sensor on COSMIC-2 to specify the true ionospheric horizontal gradients.

•  Recommend a UV photometer as a secondary payload on COSMIC-2 for high

resolution ionospheric specification and identification of irregularities which

produce scintillation.