Observations of the diurnal cycleof the OLR from GERB

Ruth Comer, Tony Slingo and Richard Allan

Environmental Systems Science CentreUniversity of Reading, UK

• Background and methodology• Results• Other related work• Conclusions, current and future work

GERB International Science Team, Met Office, Exeter, 23-25 October 2006

• We use GERB data for July 2006, with 15-minute temporal resolution

• Composite the data to produce an average diurnal cycle, according to local solar time

• Analyse using Principal Component (PC) analysis, following Smith and Rutan (2003)

Methodology

The first two Principal Components of the GERB data for July 2006 (left) and their corresponding empirical orthogonal functions (right)

The first two Principal Components of the GERB data for July 2004 V002 (left) and their corresponding empirical orthogonal functions (right)

Comparisons of the mean diurnal cycles (solid lines) with the contributions from the various Principal Components

Comparison of the second EOF with topographic features

1: Atlas mountains

2: Ethiopian highlands

3: Cameroon highlands

4: Hoggar

5: Tibesti

6: Marra plateau

7: Yemeni highlands

• PC1 shows the diurnal cycle of surface temperature• PC2 shows the diurnal cycle of convective clouds• This is a similar result to that found by Smith and

Rutan (2003), who used ERBE data, but GERB provides much higher temporal resolution and the result is much better defined

• The convective clouds are preferentially triggered by topography and over tropical Africa these clouds then advect to the west in the ambient easterly flow

Summary of results

Other work• Analysis of the diurnal cycle in HiGEM

– High resolution version of the latest Hadley Centre climate model

– http://www.higem.nerc.ac.uk/– Atmospheric model run at 90km and 60km resolution

globally (on the NERC HPCx supercomputer and on the Earth Simulator, Yokohama, through the UK-Japan Climate Collaboration)

– Similar diurnal cycle errors to previous versions of the model (deep tropical convection develops far too quickly in the day)

• Similar analysis of the operational NWP model

Summary and future work• GERB allows us to study the diurnal cycle of the

OLR with unprecedented temporal resolution– Principal Component analysis– Clear interpretation of EOFs 1 and 2 in terms of physical

modes (surface heating, cloud response)

• Paper submitted to GRL and under review– Observations of the diurnal cycle of outgoing longwave

radiation from the Geostationary Earth Radiation Budget instrument, by R.E. Comer, A. Slingo, and R.P. Allan

• Ongoing work at ESSC includes:– Diurnal cycle of convection and upper tropospheric

humidity using SEVIRI imager on Meteosat-8