1 © crown copyright 2003 gras saf user workshop helsingør, denmark, 11-13 june 2003 user...

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.


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


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


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 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 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


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)


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

1 © crown copyright 2003 gras saf user workshop helsingør, denmark, 11-13 june 2003 user...

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