João Paulo Martins (IPMA/IDL) & Rita Cardoso Pedro M. M. Soares Isabel Trigo Margarida Belo Pereira Nuno Moreira Ricardo Tomé The diurnal cycle of coastal cloudiness over west Iberia using the CM-SAF cloud data record (CLAAS) and a WRF regional climate simulation

Motivation Azores High (Subsidence) Iberia thermal Low Cold air advection Coastal upwelling High LTS ERA-Interim JJA means

Satellite observations During summer nights, clouds penetrate inland causing low ceiling and fog. During the day, the cloud deck dissipates over land Little climatological information about this process existed so far in this region Distinct diurnal cycle on coastal (Sc shallow convection) and inland regions (shallow and deep convection) SEVIRI images (10 July 2013) 0900 UTC1300 UTC 1730 UTC

CLASS: A Climate Data Record of cloud and radiation products, based on SEVIRI, onboard Meteosat Second Generation (MSG) (Stengel et al, 2013) Period: 01/01/2004 – 01/12/2011 (8 years) resolution 0.25º / hourly Radiances consistently reprocessed using state of the art algorithms Example products Cloud Fraction Cloud Top Height Cloud Phase Cloud Type Cloud Optical Depth Radiative Fluxes Etc. Ideal dataset to study the diurnal cycle of clouds over west Iberia

Mean Diurnal Cycle JJA (CM-SAF data)

SYNOP in situ observations JJA

Zonal and meridional variations of the diurnal cycle (CM-SAF data) Maximum of low clouds ~ 08 UTC Maximum deep convective clouds ~ 16 UTC Coastal orography: separation between regimes

Regional Climate Simulation using WRF WRF simulations (Soares et al, 2012) over Iberia were used to explain the observations ( ). Only common years with the CM-SAF dataset were used ( ). Simulation features: 9 km resolution. 144 x 111 points ERA-Interim boundary conditions. Nested domain over one with a coarser resolution (27km) 20 vertical levels at the boundary layer (49 total) Microphysics: WSM 6 class single-moment PBL: Mellor-Yamada-Janjic Cumulus: Betts-Miller-Janjic Soil: Noah LSM 4-layer Radiation: NCAR CAM shortwave and longwave schemes Simulation domain WRF 9km (Soares et al., 2012)

Overestimation Underestimation (in general) How well does WRF represent the observed cloud fraction? WRF - CM-SAF

What controls the limit of the cloud deck? (Conditional sampling: only offshore Sc cases) Cloudiness increased over mountains with small h/L Dynamic blocking of the flow on mountains with large h/L Marine boundary layer behaves like a gravity current Internal boundary layer (e.g. Wallace & Hobbs, 2005) Cloud enhancement Dynamic blocking of the flow

What controls the limit of the cloud deck? (Only offshore Sc cases) Zonal Meridional Vertical Strong subsidence (katabatic winds) ascent subsidence

What controls the limit of the cloud deck? (Only offshore Sc cases) Zonal Meridional Vertical Strong subsidence (katabatic winds) ascent subsidence

What controls the limit of the cloud deck? Convection Surface Microphysics PBL Radiation Subsidence warming partially compensated by diabatic processes (e.g. droplet evaporation cooling) -> Prevents further propagation of the cloud deck Potential temperature budget:

Conclusions CM-SAF CLASS dataset is useful to validate high resolution climate simulations such as the one made with WRF for Iberia (clouds and radiation) CM-SAF CLASS shows evidence of a persistent diurnal cycle of coastal clouds, confirmed by in situ measurements (SYNOP observations), with impacts on tourism, airport operations and fire risk management, among others. It is possible to distinguish between stratocumulus-topped convection and cumulus convection over land in the observed diurnal cycles In coastal regions north of the Sintra-Montejunto-Estrela mountain range, between 50 to 60% of the mornings are cloudy/overcast. Mountain and sea-breeze circulations play a key role in the progression of the cloud deck inland: Dynamic blocking of the marine boundary layer by mountains with large h/L Adiabatic heating due to subsidence.

MODIS 11/07/2013 Obrigado If you are interested, please read the paper with the full story: Martins et. al (2015): “The summer diurnal cycle of coastal cloudiness over west Iberia using Meteosat/SEVIRI and a WRF regional climate model simulation”. International Journal of Climatology (Early View)

Additional material

Day: Strong sea/mountain breeze Descending branch offshore Sensible heat flux over land Cloud deck is eroded near the coast Night: Weak breeze Descending branch over the first coastal mountain with high h/L Marine layer is able to conserve offshore properties inland LW cooling Cloud deck thickens What controls the cloud deck limit?

Minimum/Maximum/Mean JJA (CM-SAF data) Cloud Fraction (CM-SAF) MinimumMaximumMean

Hora a que ocorrem os extremos (dados CM-SAF) Time of minimum cloud fraction Time of maximum cloud fraction Hour (UTC)