# Presentation: 164094

## TIMED/GUVI Data for IRIR. DeMajistre, L.J. Paxton, D. Bilitza and H.Kil

- TIMED/GUVI Data for IRIR. DeMajistre, L.J. Paxton, D. Bilitza and H.Kil

- IRI 2005

## GUVI for the ionosphere

- What is TIMED/GUVI
- Measurement methods for the nighttime ionosphere
- Ionosonde validation
- Application – Calibration transfer
- GUVI and IRI

- Motivation for future work and collaboration rather than final results

## GUVI - Global UV Imager

**GUVI** - Global UV Imager
** ****Scanning Spectrographic Imager**
** ****Covers 115-180 nm in 160 nm spectral bins**
** ****14 cross track spatial pixels act as a linear array**

**TIMED Spacecraft**
** ****High inclination circular orbit, ~625 km altitude**
** ****Covers all local times in 60 days**
** ****Nightside passes ~25 degrees apart**

## Nightside measurements

**GUVI Colors**

-  GUVI ‘colors’ summed on board – 5 bright FUV spectral features
-  Only 2 colors are usually detected at night
-  Color 3, 135.6 nm, due almost entirely from F region recombination

## Disk Measurements

-  GUVI down-looking pixels yield slant column brightness through the F Layer
-  Can be converted to TEC with some assumptions about profile shape
-  Very high spatial resolution (~ 25x25 km) reveals bubbles and irregularities

- Composite 135.6 nm image for day 82, 2002

## Limb Measurements

-  First 32 steps of each scan are on the limb (100 – 520 km)
-  Constrained linear inversion yields volume emission rate/electron densities

**Systematic monitoring of the nighttime F Region**

## Monitoring the Ionosphere

- Coverage
- Altitude – Each scan, 150 – 500 km
- Latitude – Each orbit
- Longitude – Each day
- Local time – 60 days
- Over 3 years of data yields seasonal coverage as well
- Limits
- Low signal levels away from the anomalies
- Assumption of spherical symmetry
- Recombination rate is uncertain
- Assumes one constituent ionosphere (O+)

## Global Observations

-  Electron densities can be used to estimate NMF2
-  Coverage allows global maps
-  Orbit precession rate allows inter-annual comparisons
-  Can be compared directly with ionosonde data or IRI

## Ionosonde Comparisons

-  GUVI electron density profile fit with a Chapman layer
-  NMF2 and HMF2 taken directly from the fit
-  Same process can be used with IRI

## Ionosonde Data

| Station | Lat. | Long. |
| --- | --- | --- |
| Juliusruh, Germany | 54.6 | 13.4 |
| Wakkanai, Japan | 45 | 141 |
| Ebro, Spain | 40.8 | 0.5 |
| Kokubunji, Japan | 35 | 139 |
| Yamagawa, Japan | 31 | 130 |
| Delhi, India | 28.6 | 77.2 |
| Okinawa, Japan | 26 | 128 |
| Waltair, India | 17 | 83 |
| Trivandrum, India | 8.3 | 76.6 |
| Sao Luis, Brazil | -2.3 | 315.8 |
| Fortaleza, Brazil | -3.9 | 321.5 |
| C. Paulista, Brazil | -22.7 | 315 |
| B. Aires, Argentina | -34.6 | 301.7 |
| Concepcion, Chile* | -36.8 | 287 |
| Cachimbo, Brazil | -9.5 | 305.2 |

** ****Ionosonde Data Supplied to from the various stations**
** ****Data from other stations was supplied but had no suitable GUVI coincident measurement**

## GUVI Selections

- Criteria for selecting coincidences
- Within 200 km and 20 minutes
- Chapman layer fit successful
- Good fit to data
- Realistic HMF2 and NMF2
- No ‘qualifying letters’ on ionosonde data
- 427of  1112 observations met these criteria

##  GUVI and IRI have similar spread (~30-40%)

** ****GUVI and IRI have similar spread (~30-40%)**
** ****GUVI compares well between 0.5 and 1.0 (10****6**** cm****-3****)**
** ****IRI bias similar in shape to GUVI **
** ****Both GUVI and IRI show ‘discontinuity’ at 1.0 (10****6**** cm****-3****)**

## IRI/GUVI comparison

-  Similar spread as (~30%)
-  At higher NMF2, GUVI systematically low
-  Slope of bias is constant (suggests calibration of GUVI is reasonable)

## Conclusion of comparisons

-  At moderate NMF2, GUVI predicts ionosonde measurements with 30% or so
-  In the same range, IRI behaves the same way with a fairly large positive bias
-  At larger NMF2 both under-predict

## Calibration Transfer

- The issue – Ionosonde intercalibration
-  Various instrument designs
-  Separate calibrations
-  Independently operated
- Example solution – Ozone monitors
- ‘Standard instrument’ carried from site to site
- Makes simultaneous measurements
- Suggested approach – Orbiting UV monitoring
- Use GUVI (and/or its successors) to transfer calibration

## Slide 16

## Regional Analysis - significant geographic differences

## Inter-ionosonde Comparisons

- Significant differences between stations
- Significant regional differences
- GUVI statistics can be used to identify areas that may need attention
-  In principle, GUVI measurements should have little geographic dependence
- Geographic differences in profile shapes and horizontal gradients may have some influence

## GUVI and IRI - Conclusions

- GUVI can provide systematic observations
- Can be used to compare with IRI
- Once differences are understood, observations can be included in IRI
- GUVI can be used to refine ionosonde measurements
- Provide better IRI validation
- Provide better IRI input