Simulations of Vertical Water Vapor Transport for TC Ingrid (2013)

Abstract

Vertical water vapor transport is examined for tropical cyclone (TC) Ingrid (2013), a Category 1 storm in the Gulf of Mexico that contained deep convection, including numerous overshooting tops. The study employs high-resolution numerical simulations using the Weather Research and Forecasting model with a smallest grid spacing of 1.33 km and a model top of 10 hPa (~31 km) that extends into the lower stratosphere. Area-averaged values of vertical motion, water vapor content, its temporal change, and vertical water vapor transport are presented for Ingrid as a whole and for individual regions of the storm. Results show that area-averaged hydration in the layer~1-14.5 km between the start and end of the simulation (4.75 days) is due to upward convective transport. Observed overshooting convection is simulated, revealing intense vertical motions that transport large quantities of vapor and ice to the lower stratosphere. Greatest dehydration occurs in the upper troposphere and lower stratosphere between 14.5 and 17.5 km. This layer is found to be supersaturated with respect to ice. This apparently caused water vapor to deposit on the convectively lofted ice, allowing it to then grow and sediment out of the layer, thus producing dehydration. Conversely, hydration occurred between 17.5 and 21 km due in part to that layer being subsaturated with respect to ice. Overall, the study highlights the important role TCs and their embedded overshooting convection play in transporting water vapor to the upper troposphere and lower stratosphere.

Simulation of Chemical Transport by Typhoon Mireille (1991)

“…This suggests that vertical flux (by itself) leads to increasing chemical concentrations. Current results for water vapor are consistent with prior TC studies that have found a positive net water vapor flux throughout the troposphere (e.g., Allison et al, ; Wang, ). However, to our knowledge, this is the first study to calculate CO and O 3 flux profiles for a TC.…”

“…Areas of the cells at tropopause altitude are all less than 0.4% of the total area of Mireille. Their heights above the tropopause range from 0.3 to 1.5 km (16.3 km to 17.5 km above sea level), consistent with previous studies (e.g., Allison et al, ; Pan et al, ; Tao & Jiang, ). However, they are slightly higher than those reported for Mireille by NE96 who found tops exceeding 15.5 km based on observed cloud top temperatures and vertical temperature profiles from the Japanese Geostationary Meteorological satellite.…”

“…To summarize, fluxes and concentrations of trace gases associated with Mireille compare well to those from similar studies of TCs, middle‐latitude cyclones, and mesoscale convective systems. For example, Mireille's net water vapor flux was similar to that of Ingrid (Allison et al, ). Values of CO transport (i.e., flux density and concentration) also compared well to middle‐latitude convection over East Asia (Klich & Fuelberg, ) and the central United States (Li et al, ).…”

“…However, Randel et al () found that strong convection during Northern Hemisphere summer monsoons actually dehydrates the stratosphere because convection is linked to large‐scale cooling responses in the subtropics. Similarly, Allison et al () found that the greatest dehydration during TC Ingrid (2013) occurred in the UTLS (~15.5 km) due to the deposition of water vapor on ice crystals in this cold region (Jensen et al, ; Sherwood & Dessler, , ).…”

“…Mireille's total area was defined as a prescribed radius from its eye because of the storm's symmetric structure and relatively constant size during the focus period. Various radii have been used in prior studies, including 100-200 km (e.g., Raju et al, 2011), 300 km (e.g., Allison et al, 2018), 400 km (e.g., Halverson et al, 2006), 500 km (e.g., Tao & Jiang, 2013), and 500-1,000 km (e.g., Romps & Kuang, 2009). Testing of these radii on various meteorological fields, including composite reflectivity and 10-m winds, revealed that an~900-km (8.3°) radius best encompassed Mireille's circulation at the time of DC-8 chemical sampling (27 September).…”