1 © Crown copyright 2003
GRAS SAF User Workshop Helsingør, Denmark, 11-13 June 2003
User Requirementsfor GRAS SAF RO Products
Dave Offiler
GRAS SAF User Workshop Helsingør, Denmark, 11-13 June 20032 © Crown copyright 2003
Background Generic (technology-free) URs for temperature &
humidity profiles traceable to WMO/CBS
Reviewed by APM (“Granada-1”), GRAS SAG, CLIMAP & GRAS SAF 1st User Workshop
Also feedback from URs for other RO missions (WATS, ACE+)
Adapted for constraints of RO technique and in particular the GRAS on Metop mission, via the EURD
URD specifies general & specific requirements on GRAS SAF data products.
GRAS SAF User Workshop Helsingør, Denmark, 11-13 June 20033 © Crown copyright 2003
Main Drivers - NWP Objective: Short to medium range weather
forecasting (hours to a few days)
F/c initialisation fields optimum wrt true state of atmosphere (assimilation)
Rapid availability of global observational data
Quality control to maintain a priori expected error characteristics (Gaussian, zero bias)
Errors well characterised
GRAS SAF User Workshop Helsingør, Denmark, 11-13 June 20034 © Crown copyright 2003
Main Drivers - Climate Objective: detect & monitor long-term climate
change Long duration, continuous data sets with
homogeneous, global coverage; diurnal effects unaliased
Long-term stability (no bias drift) Accurate temperature & humidity profiles Monthly (or annual) grid box means (Level 3) Validation of CGMs Initialisation of CGMs from NWP (re-)analyses
GRAS SAF User Workshop Helsingør, Denmark, 11-13 June 20035 © Crown copyright 2003
Atmospheric Layers
HigherStratosphere (HS)
10 – 1 hPa(35 – 50 km)
LowerStratosphere (LS)
100 – 10 hPa(15 – 30 km)
HigherTroposphere (HT)
500 – 100 hPa(5 – 15 km)
LowerTroposphere (LT)
1000 – 500 hPa(Surface to 5km)
1 h
WMO Definition of Atmospheric Layers
GRAS SAF User Workshop Helsingør, Denmark, 11-13 June 20036 © Crown copyright 2003
GRAS Mission Observation Requirements (NWP)
TemperatureSpecific
HumiditySurfacePressure
RefractivityBending
AngleHorizontalDomain
Global Global Global Global Global
HorizontalSampling
100–2000km100 –
2000km100–2000km 100–2000km
100–2000km
VerticalDomain
Sfc–1 hPa Sfc–100 hPa Sfc (msl) Sfc–1 hPa Sfc–80 km
VerticalSampling
LTHTLSHS
0.3–3km1–3 km1–3 km1–3 km
0.4–2 km1–3 km
––
––––
0.3–3 km1–3 km1–3 km1–3 km
¦ ¦ ¦ 2–5 Hz ¦
TimeWindow
1–12 hrs 1–12 hrs 1–12 hrs 1–12 hrs 1–12 hrs
RMSAccuracy 4)
LTHTLSHS
0.5–3 K0.5–3 K0.5–3 K0.5–5 K
0.25–1 g/kg 5)
0.05–0.2g/kg5)
––
0.5–2 hPa–––
0.1–0.5%0.1–0.2%0.1–0.2%0.2–2%
¦ 1 rad¦ or¦ 0.4% 7)
¦Timeliness 1-3 hrs 1–3 hrs 1–3 hrs 1–3 hrs 1–3 hrs
GRAS SAF User Workshop Helsingør, Denmark, 11-13 June 20037 © Crown copyright 2003
GRAS Mission Observation Requirements (Climate)
Temperature Specific HumidityHorizontal Domain Global Global
HorizontalResolution 1)
LTHTLSHS
50–500 km50–500 km50–500 km50–500 km
50–100 km50–100 km50–250 km50–250 km
Vertical Domain Surface to 1 hPa Surface to 1 hPa
VerticalResolution 2)
LTHTLSHS
0.3–3 km1–3 km1–3 km
5–10 km
0.5–2 km0.5–2 km0.5–2 km1–3 km
Time Resolution 3) 3–12 hrs 3–12 hrs
RMSAccuracy 4)
LTHTLSHS
0.5–3 K0.5–3 K0.5–3 K
1–3K
0.25–1 g/kg 6)
0.025–0.1 g/kg 6)
0.0025–0.01 g/kg 6)
0.00025–0.001 g/kg 6)
Timeliness 30–60 days 30–60 daysTime Domain > 10 years > 10 yearsLong-term Stability < 0.1 K/decade < 2% RH/decade
GRAS SAF User Workshop Helsingør, Denmark, 11-13 June 20038 © Crown copyright 2003
Products & Processing Profiles of corrected refraction (bending angles) -
Level 1b Profiles of refractivity - Level 2a Profiles of temperature, humidity & pressure -
Level 2b For climate, use of a consistent processing
methodology (re-processing whole mission) For NWP, availability in NRT (<3hrs)
GRAS SAF User Workshop Helsingør, Denmark, 11-13 June 20039 © Crown copyright 2003
User Requirements Document URD is a base document in the GRAS SAF
documentation tree - almost all other documents flow from it. SAF operational performance will be judged against the URD
URD contains much more detail than presented here, including specific requirements, cross-referenced elsewhere
URD is stable but not fixed; can evolve in a controlled way
Real user feedback on URD (or products defined by it) are always welcome