TRAMS: A new dynamic cloud model for Titan's methane clouds

Abstract

Convective clouds on Titan may play an important role in climate dynamics, atmospheric chemistry, and the overall volatile cycle. To study the formation and evolution of these clouds, we have developed the Titan Regional Atmospheric Modeling System (TRAMS). TRAMS is a three‐dimensional, time‐dependent, coupled fully compressible dynamic and microphysical model capable of simulating methane and ethane clouds in Titan's atmosphere. In initial model tests over a two‐dimensional domain, a warm bubble or random temperature perturbations trigger a parcel of air to rise. For an initial methane profile with a 60% surface humidity, convection occurs for positive temperature perturbations of 1 K or greater. Cloud tops are between 25 and 35 km, consistent with observations of the south polar clouds. For a drier methane environment in the lower atmosphere, characteristic of the Huygens landing site, convection does not occur, but a layer of stratiform clouds is able to form at altitudes around 10 km.

Titan's Tropical Storms in an Evolving Atmosphere

“…While clouds may be more numerous (Mitchell et al 2006), we find that convection however is still very weak with a CAPE∼160 J kg Ϫ1 and LNB p 26 km, in agreement with Barth & Rafkin (2007) yet not (Tokano et al 2006b) as a result of differing lapse rates (Appendix B). An increase in the surface temperature by 2 K (larger than predicted by GCM models [Tokano 2005]) would also initiate surface convection, but again does not change the CAPE significantly from that of Titan's current atmosphere.…”

“…Yet, Barth & Rafkin (2007) calculate a CAPE p 60 J kg and Ϫ1 LNB p 19 km, which disagrees as a result of their different wet lapse rate. Their study indicates an atmosphere devoid of strong convective systems, consistent with near-IR images of Titan's tropical atmosphere (possible over the past 10 years), which detect no evidence of large convective cloud systems or rainfall (Brown et al 2002;Roe et al 2002;Gibbard et al 2004;Adamkovics et al 2005;Porco et al 2005;Hirtzig et al 2006;Schaller et al 2006a).…”

“…An increase in the surface temperature by 2 K (larger than predicted by GCM models [Tokano 2005]) would also initiate surface convection, but again does not change the CAPE significantly from that of Titan's current atmosphere. Only variations in Titan's humidity below 9 km strongly affect its stability (Barth & Rafkin 2007;Hueso & Sánchez-Lavega 2006). A surface humidity of 60% produces a CAPE of 860 J kg (Fig.…”

Meridional variation in tropospheric methane on Titan observed with AO spectroscopy at Keck and VLT

“…Clouds of methane can indicate regions of convection (e.g., Griffith et al, 2005), polar subsidence , or evaporation from lakes (e.g., $ Accepted for publication on May 22, 2015 Email address: mate@berkeley.edu (MátéÁdámkovics) URL: http://astro.berkeley.edu/~madamkov (MátéÁdámkovics) Brown et al, 2009;Turtle et al, 2009), while the formation of large scale methane cloud systems are diagnostic of atmospheric dynamics via their morphology (Mitchell et al, 2011) and how they evolve with time (Ádámkovics et al, 2010;Turtle et al, 2011a). The amount of methane near the surface is an important factor in triggering convective cloud formation (Barth and Rafkin, 2007) and in determining the strength of storms (Hueso and Sánchez-Lavega, 2006). Precipitation can return methane to the surface (Turtle et al, 2009 where fluid transport has some role in closing the hydrological cycle.…”

AVIATR—Aerial Vehicle for In-situ and Airborne Titan Reconnaissance

“…Convective clouds at Titan's southern midlatitudes have been observed to evolve vertically on short (30 min) timescales with updraft velocities of ∼10 m/s [45]. Convective cloud altitudes can be used as a probe of the stability and humidity profile of Titan's atmosphere [13,47,48,53]. AVIATR, flying at altitudes of 3-14 km, is perfectly positioned to observe cloud base formation and subsequent cloud evolution with the Horizon-Looking Imager (HLI).…”