Evaluating the Future of Lightning in Cloud‐Resolving Models

Abstract

Two proxies for lightning predict very different responses to global warming: the CAPE times precipitation proxy predicts a large increase in lightning over both the continental United States and the tropical oceans, while the ice flux proxy predicts a small increase over the United States and a decrease over the tropical oceans. To date, however, these proxies have been studied only in global climate models with parameterized convection. Here, cloud-resolving simulations are used to assess their predictions of future lightning rates. Over the United States, all proxies predict a large increase in the lightning rate in the range of 8-16%/K. On the other hand, in the tropics as modeled by radiative convective equilibrium, half of the proxies predict an increase (of 5-12%/K), while the other half predict a decrease (of 1-4%/K). The reasons for the different responses of these proxies is explored, but it remains unclear which proxy is best suited to predicting future lightning rates. SimulationsThe analysis presented here will take advantage of two sets of simulations available from other studies: a pair of 13-year-long cloud-resolving simulations over CONUS (RM. Rasmussen & Liu, 2017) and three 4-year-long cloud-resolving simulations of tropical radiative convective equilibrium (RCE) over a slab ocean. WRF Simulations of CONUSThe pair of cloud-resolving simulations over CONUS were conducted with the Weather Research and Forecasting (WRF) model v3.4.1 using a 4-km horizontal grid spacing (RM. Rasmussen & Liu, 2017). Key Points:• Lightning proxies are studied in cloud-resolving simulations of global warming over the United States and the tropical ocean • All the proxies predict that lightning increases over the United States in the range of 8-16% per kelvin • The proxies disagree over the tropical ocean, predicting either a substantial increase of 5-12%/K or a moderate decrease of 1-4%/K Supporting Information:• Supporting Information S1

Estimates of lightning NO<sub><i>x</i></sub> production based on high-resolution OMI NO<sub>2</sub> retrievals over the continental US

“…As a result of the different effects on radiative forcing from ozone and methane, a net positive radiative forcing was found with the CTH approach while there is little net radiative forcing with the IFLUX approach (Finney et al, 2018). However, the convective available potential energy (CAPE) times the precipitation rate (P ) proxy predicts a 12 ± 5 % increase in the continental US (CONUS) lightning strike rate per kelvin of global warming (Romps et al, 2014), while the IFLUX proxy predicts the lightning will only increase 3.4 % K −1 over the CONUS. Recently, Romps (2019) compared the CAPE ×P proxy and IFLUX method in cloud-resolving models.…”

“…In view of the regionally dependent lifetime of NO x and the difficulty of measuring LNO x directly, a better understanding of the LNO x production is required, especially in the tropical and midlatitude regions in summer. Using its distinct spectral absorption lines in the near-ultraviolet (UV) and visible (VIS) ranges (Platt and Perner, 1983), NO 2 can be measured by satellite instruments like the Global Ozone Monitoring Experiment (GOME;Richter et al, 2005), SCanning Imaging Absorption SpectroMeter for Atmospheric CHartographY (SCIA-MACHY; Bovensmann et al, 1999), the Second Global Ozone Monitoring Experiment (GOME-2; Callies et al, 2000), and the Ozone Monitoring Instrument (OMI; Levelt et al, 2006). OMI has the highest spatial resolution, least instrument degradation, and longest record among these satellites (Krotkov et al, 2017).…”

Regional variability in lightning activity over South Asia

“…Some of them have been discussed in the Introduction of this paper. Recently, Romps et al (2014), Romps et al, 2018) and Romps (2019) have successfully used a multiplication of CAPE and precipitation rate as a proxy for contiguous United States. It needs to be cautioned, however, that use of such correlations between parameters does not necessarily imply as causality.…”

“…Simulation of lightning in weather and climate models still remains a challenging problem (Price, 2009; Finney et al ., 2018; Romps, 2019). There is no concrete evidence of a single parameter that could be used to forecast lightning.…”

African Lightning and its Relation to Rainfall and Climate Change in a Convection‐Permitting Model

“…Jacobson and Streets (2009) and Finney et al (2018) use coarse resolution models which parametrize convection, thereby limiting their ability to simulate tropical convective storms. Romps (2019), who investigated cloud-to-ground lightning, uses a much higher resolution model. However, the model is based upon radiative-convective equilibrium and consequentially only applies over the tropical ocean, where there is relatively weak lightning activity.…”