Nicholas Engerer

Surface Characteristics of Observed Cold Pools

Abstract Cold pools are a key element in the organization of precipitating convective systems, yet knowledge of their typical surface characteristics is largely anecdotal. To help to alleviate this situation, cold pools from 39 mesoscale convective system (MCS) events are sampled using Oklahoma Mesonet surface observations. In total, 1389 time series of surface observations are used to determine typical rises in surface pressure and decreases in temperature, potential temperature, and equivalent potential temperature associated with the cold pool, and the maximum wind speeds in the cold pool. The data are separated into one of four convective system life cycle stages: first storms, MCS initiation, mature MCS, and MCS dissipation. Results indicate that the mean surface pressure rises associated with cold pools increase from 3.2 hPa for the first storms’ life cycle stage to 4.5 hPa for the mature MCS stage before dropping to 3.3 hPa for the dissipation stage. In contrast, the mean temperature (potential tem...

Categorizing the Meteorological Origins of Critical Ramp Events in Collective Photovoltaic Array Output

AbstractPhotovoltaic (PV) solar power use is increasing globally. The Australian Capital Territory (ACT) has legislated a renewable energy target of 90% by 2020; to reach this target, use of distributed PV solar arrays is expected to increase. Cloud cover can cause the power output of PV installations to rapidly increase or decrease, resulting in ACT-wide collective ramp events. Accurate forecasts of when the ramp events will occur are needed for electricity providers to plan for these abrupt output changes and to ensure that electricity supplies remain stable. This paper categorizes the weather events that cause changes in the output of rooftop PV arrays in the ACT, providing a foundation for future PV output forecasting to be based on weather event identification. This paper identifies citywide collective ramp events, which occur when a 60% change in collective PV power output (with respect to the clear-sky potential) is experienced within 60 min. Such events are termed critical collective ramp events. ...

A cloud displacement estimation approach for sky images based on phase correlation theory

For intro-hour solar power forecasting approaches with sky images, the computing for cloud motion is very necessary. In this paper, a cloud displacement estimation method for sky images based on phase correlation theory is proposed. By Fourier transforming, the image matrix in frequency domain is obtained and then the cross-power spectrum of two adjacent sky images can be calculated. According to the inverse Fourier transform of the cross-power spectrum, the displacement of cloud in the two adjacent sky images is achieved. To improve the practical application ability of the approach, the noise signal in cross-power spectrum is analyzed and a filtering method to exclude erroneous results is also provided. Simulation results showed the effectiveness of the proposed method.