Abhnil A. Prasad

Mesoscale simulations of Australian direct normal irradiance, featuring an extreme dust event

AbstractDirect normal irradiance (DNI) is the main input for concentrating solar power (CSP) technologies—an important component in future energy scenarios. DNI forecast accuracy is sensitive to radiative transfer schemes (RTSs) and microphysics in numerical weather prediction (NWP) models. Additionally, NWP models have large regional aerosol uncertainties. Dust aerosols can significantly attenuate DNI in extreme cases, with marked consequences for applications such as CSP. To date, studies have not compared the skill of different physical parameterization schemes for predicting hourly DNI under varying aerosol conditions over Australia. The authors address this gap by aiming to provide the first Weather and Forecasting (WRF) Model DNI benchmarks for Australia as baselines for assessing future aerosol-assimilated models. Annual and day-ahead simulations against ground measurements at selected sites focusing on an extreme dust event are run. Model biases are assessed for five shortwave RTSs at 30- and 10-k...

Decadal changes in thin cirrus height measured by MISR

Thin cirrus clouds are difficult to detect and the operational cloud-height product from the Multiangle Imaging Spectro Radiometer (MISR) may miss thin cirrus when it overlies thicker, lower-level cloud. To detect thin cirrus over clear skies with MISR, cloud-heights above 10 km were retrieved using a stereo matching technique on the oblique camera pairs and re-projected onto the nadir camera after correction for parallax and winds. A merged dataset, including measurements from the CERES broadband radiometer, was used to compare measured outgoing longwave radiation (OLR) to the OLR from a column model of longwave radiative transfer that uses MISR cloud-top heights and reanalysis data as input parameters. After accounting for uncertainties in modeled OLR of ± 4 W m−2 due to uncertainties in the input properties, especially for known high cloud, surface temperature and specific humidity, the average difference of 17 W m−2 cannot be directly explained, and is accounted for by the addition of thin cirrus with...

Fluctuations in cloud-top height measured by CALIPSO from 2006-2015

The inception of space-borne lidar has added vital information on clouds vertical profile and distribution over the globe. This includes CALIPSO (Cloud-Aerosol Lidar and Infrared Pathfinder Satellite Observations), which has been screening clouds with CALIOP (Cloud-Aerosol Lidar with Orthogonal Polarization) consistently from mid 2006. CALIOP cloud-top height (CTH) measurement capability exists for layers with optical depth (τ > 0.01), allowing it to detect subvisual and thin cirrus with high confidence. The CTH forms an essential parameter in understanding the role of clouds on climate, especially fluctuations in the effective CTH is significant in determining the cloud-feedback. Using CALIPSO Level 2 cloud layer product with a 5 km horizontal resolution from mid 2006-2015, fluctuations in effective CTH are shown for the tropics and the whole globe.