Adjoint‐based forecast sensitivities of Typhoon Rusa

Abstract

Sensitivities of the forecast to changes in the initial state are evaluated for Typhoon Rusa, which passed through the Korean Peninsula in 2002, to understand the impact of initial condition uncertainties on the forecast and thence to diagnose the sensitive regions for adaptive observations. To assess the forecast sensitivities, adjoint‐based sensitivities were used. Sensitive regions are located horizontally in the right half circle of the typhoon, and vertically in the lower and upper troposphere which coincide with the inflow and outflow regions near the typhoon. Forecast error is reduced around 18% by extracting properly weighted adjoint‐based forecast sensitivity perturbations from the initial state, and the correction occurs primarily in the lower to mid‐troposphere where the forecast error is the largest. In contrast to the improvement in the overall forecast, the track and intensity forecast are not improved much through the modification of the initial condition by adjoint‐based forecast sensitivities.

Application of Adjoint-based Forecast Sensitivities to Asian Dust Transport Events in Korea

“…d Energy-weighted forecast error for each iteration process. R represents the response function similar to large sensitivities in the lower to midtroposphere in the case of extratropical cyclones (e.g., Kleist and Morgan 2005) and quite different from large sensitivities in the lower and upper troposphere in the case of tropical cyclones (e.g., Kim and Jung 2006). Sensitive regions for relatively long forecast lead times are located over areas without observational data.…”

“…Klinker et al (1998) suggested that "key analysis error" can be estimated by iteratively applying the adjoint-based forecast sensitivity to the initial condition. Based on this concept, adjoint-based forecast sensitivity has been used to reduce uncertainties in the analysis and to understand the dynamical evolution of initial condition uncertainties of tropical cyclones (e.g., Kim and Jung 2006) as well as extratropical cyclones (e.g., Kleist and Morgan 2005). But few studies have used adjoint-based forecast sensitivity to assess the initial condition uncertainties and sensitive regions of Asian dust forecasts.…”

Statistical adjoint sensitivity distributions of meteorological forecast errors of Asian dust transport events in Korea

“…2), we selected an energy-based forecast error measure inside a cube encompassing the tropospheric depth surrounding most of the Korean Peninsula at the verification time, instead of using the low-level pressure forecast error. The energy norm has been used in many predictability studies of extratropical and tropical cyclones (Rabier et al, 1996;Gelaro et al, 1998;Klinker et al, 1998;Kleist and Morgan, 2005;Kim and Jung, 2006;Jung and Kim, 2009) because it provides a convenient and physical way of combining forecast errors with separate model variables. Vertically, the response function of the energy forecast error is defined from the surface to 300 hPa of the model domain because the forecast errors associated with both the surface weather system and the 500 hPa trough are important for accurate atmospheric transport prediction for Asian dusts.…”

“…(1 ) (Langland et al, 2002;Kim and Jung, 2006;Kim et al, 2011 The sensitivity frequency is calculated as follows:…”

“…Until recently, many studies used adaptive observation strategies to identify sensitive regions for adaptively observing extratropical or tropical cyclones (e.g. Reynolds, 2005, 2006;Kim and Jung, 2006;Majumdar et al, 2006;Wu et al, 2007;Kim et al, 2008aKim et al, , 2011Kim and Jung, 2009a, b;Jung et al, 2010;Park et al, 2013).…”