# Presentation: 004619

## Surveying Green Light: 

**Impacts of Space Weather**

- Joseph Kunches,
- Mihail Codrescu, Tim Fuller-Rowell
- Space Weather Prediction Center
- (nee Space Environment Center)
- National Centers for Environmental Prediction
- National Weather Service
-  Boulder, Colorado

- CORS Users' Forum
- Fort Worth
- September 25, 2007

## Summary of GPS Errors

**     ****Typical Error  [m]           Standard GPS****	****	****         Differential GPS**
**          ****(per satellites)**
**Satellite Clocks****	****	****1.5****	****	****	****            0**
**Orbit Errors****	****	****	****2.5****	****	****	****            0**
**Ionosphere****	****	****	****5.0****	****	****	****            0.4**
**Troposphere****	****	****	****0.5****	****	****	****            0.2**
**Receiver Noise****	****	****0.3****	****	****	****            0.3**
**Multipath****	****	****	****0.6****	****	****	****            0.6**
**  ****The ionosphere is the largest source of error for Standard GPS and second largest for Differential GPS.**
- http://www.trimble.com/gps/howgps-error2.shtml#3

## Ionosphere and Plasmasphere

- Less than 1% of constituents ionized
- Lower boundary at ~ 60 km
- Upper boundary at ~ 1000 km
- Plasmasphere extends to several RE and includes the radiation belts and the ring current

## Ionospheric Effects on GPS

-    propagation of signals from the satellite to the receiver,
-    which affects positioning.
- The delay calculation requires modeling the electron
-    density along the pass of the signal.

## Electron\Ion Density Profile

## Ionospheric Effects

-  Neutral composition
-        Affects production and loss of ionization
-        Can vary on several hours time-scales during storms
-  Neutral Winds
-        Redistribute plasma paralell to B field
-        Change charged particle life times
-        Have time scales of about one hour
-  Electric fields
-        Redistribute plasma perpendicular to B field
-        Change charged particle life times
-        Have time scales of minutes

## Regional Composition Changes and Ion Density 

**Observations:  **
**Paxton et al. 2001**

**Modeling**

**Increase in N****2**

**Ionospheric depletion**

## Wind & Electric Field Effects

**Notes:**
Both neutral winds and E-fields can transport charged particles, creating structure in electron density and TEC.
The structures created by neutral winds and E-fields during storms are not captured by climatological models.

## Integrated particle power 5 - 100 GW on minutes time scales

## Ionospheric Corrections

- Need to model the ionosphere to compute corrections
- Empirical climatological models:  Klobuchar coefficients
- Physics based numerical models: CTIPe, TIE-GCM
- Data assimilation schemes: US-TEC, GAIM
-  Models can provide both specification and forecast
- The ionosphere is highly variable in space and time

## New Products

- Gradient Detection
- OPUS Ionospheric Correction Function

## Gradient Detection

- TEC “walls”:
- 130 TEC units over 50 km
- 20 m of GPS delay;
- walls move 100 to 500 m/s

- SED?

- “wall”

- Courtesy: Tom Dehel, FAA

## Background/Rationale

- NGS was running US-TEC in 3-day latent mode
- As the space weather agency, SWPC to provide ionospheric correctors
- Avoid the need to continue to update ionospheric activities at NGS every time SWPC makes an improvement to services
- SWPC is the natural place for providing the service of characterizing the ionosphere

## Proposal

- SWPC to provide a web-based customer application for providing ionospheric correctors from a user specified list of options
- User submits a RINEX file over a particular interval
- SWPC either uses “best-available” model to evaluate correctors or user specified model (e.g. US-TEC, GAIM, IRI, rtIRI, ....)
- Return RINEX file to user with correctors inserted
- Next version of RINEX format has place for corrector

## Ionosphere Correction for NGS 

- US-TEC slant TEC provides ionospheric correctors for  RINEX files

## USTEC Product 

- Current NOAA capability for characterizing the total number of free electrons (TEC) in the ionosphere, with parallel input data streams for reliability
- Since 2004, a product characterizing the ionospheric TEC over the continental US (CONUS) has been running in real-time at NOAA’s Space Environment Center (SEC)
- The ionospheric data assimilation model uses a Kalman filter and ingests ground-based GPS data to produce 2-D maps of total electron content over the CONUS
- Product evolved from a collaboration between SEC and NOAA’s National Geodetic Survey (NGS), National Geophysical Data Center (NGDC), and Forecast Systems Laboratory (FSL)

**Primary Product:**
**Real-time ionospheric maps of total electron content every 15 minutes. Currently uses about 100 real-time GPS stations from the CORS network**** **

***http://www.swpc.noaa.gov/ustec***

## Slant-Path TEC Maps

- Applications:
- Ionospheric correction for single frequency GPS;  NDGPS positioning;
- dual-frequency integer ambiguity resolution for rapid centimeter accuracy positioning**  **

- Sat. 1

- Sat. 5

- Sat. 14

- Sat. 29

**...****.****etc**

- A

- A

- A

- A

- B

- B

- B

- B

- C

- C

- C

- C

**Notes:**
Work horse of the product are 2-D maps of slant path TEC over the CONUS for each GPS satellite in view updated every 15 minutes 
Provides the information needed to estimate the group delay or phase advance for the GPS signals anywhere in the CONUS

##  Validation Summary

- Differential TEC:
- Slant  = 2.4 TEC units
- Vertical = 1.7 TEC units
- “Absolute” FORTE ray tracing:
- Slant = 2.7 TEC units
- Vertical = 1.9 TEC units

-  Estimated USTEC _slant path_ total electron content uncertainty < _3 TEC units_ (equivalent to about _45 cm_ of signal delay at L1 frequencies)
-  Estimate USTEC _vertical_ total electron content uncertainty < _2 TEC units_ (equivalent to about _30 cm_ of signal delay at L1 frequencies)

## SWPC Ionosphere Goals

-  **Improve USTEC**
-   CONUS: Specification
-      US-TEC _slant path_ total electron content uncertainty < _2 TECU _
-      US-TEC _vertical_ electron content uncertainty < _1 TECU_
-   CONUS: Forecast
-       1 hour forecast as good as specification
-       3 hour forecast: uncertainty < _3 TEC units_
-       6-12 hour forecasts
-   GPS User Tools
-        Color coded regional maps of ionosphere disturbance
-        Support vendors to produce color coded maps for specific applications

**Notes:**
Global specification and forecast requires global, real-time data sets and we are actively working to acquire them (COSMIC, IHY Africa, National Geospatial-Intelligence Agency (NGA), EUREF-IP service, etc.). 
The future of ionosphere services is in accurate forecast. 
1-3 hour forecasts over CONUS are possible with the present models. 
Longer forecasts and forecasts at high and low latitudes require thermosphere/ionosphere numerical models and accurate inputs. 

## Conclusions

**Solar Maximum is on the way (2012?)**

**Ionospheric services are a fast growing area in Space Weather**
**SWPC is committed to offer improved products and tools**
**SWPC is ready to collaborate on:**
-       Data
-       Models and model results
-       Research
-       Services

## Ion Production

**O****2 ****+ h******** ******** O****2****+**** + e  (1028 Å)**

**N****2 ****+ h******** ******** N****2****+**** + e  (795 Å**)

## From Rodney Viereck, SEC

**Notes:**
Flare is X class

- The solar x-ray images are from the Yohkoh mission of ISAS, Japan. The x-ray telescope was prepared by the Lockheed Palo Alto Research Laboratory, the National Astronomical Observatory of Japan, and the University of Tokyo with the support of NASA and ISAS. G.L. Slater and G.A. Linford