Modelling tropical convection: comparison with observations (original) (raw)
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Do Undiluted Convective Plumes Exist in the Upper Tropical Troposphere?
Journal of the Atmospheric Sciences, 2010
Using a passive tracer, entrainment is studied in cloud-resolving simulations of deep convection in radiative–convective equilibrium. It is found that the convective flux of undiluted parcels decays with height exponentially, indicating a constant probability per vertical distance of mixing with environmental air. This probability per distance is sufficiently large that undiluted updrafts are negligible above a height of 4–5 km and virtually absent above 10 km. These results are shown to be independent of the horizontal grid size within the range of 3.2 km to 100 m. Plumes that do reach the tropopause are found to be highly diluted. An equivalent potential temperature is defined that is exactly conserved for all reversible adiabatic transformations, including those with ice. Using this conserved variable, it is shown that the latent heat of fusion (from both freezing and deposition) causes only a small increase in the level of neutral buoyancy near the tropopause. In fact, when take...
Spatial and temporal variation of water vapor mixing ratio (WVMR) is examined for its association with the convective activity in upper troposphere and lower stratosphere over tropical region particularly Asian monsoon region (AMR) and Indonesian–Australian West Pacific region (IAWPR) using WVMR obtained from MLS satellite with simultaneous daily mean OLR from NOAA and daily mean wind from NCEP reanalysis. An examination of WVMR at various pressure levels during high water vapor regime (moist Phase) indicates that water vapor (WV) transport, in troposphere, is rather fast up to a level of ~ 147 hPa. Seasonal variation of WVMR over tropical lower stratosphere (TLS) is noted to be closely associated with seasonal northward movement of intertropical convergence zone (ITCZ). Convection activity over AMR appears to be a prominent contributor to the moist phase of WVMR seasonal cycle in TLS. However, other tropical regions may also be contributing to the seasonal variability of WVMR. Low WV (dry) phase of the WVMR seasonal cycle in TLS observed during NH winter and early spring months may be caused by the appearance of extreme cold temperatures (≤ 191 K) close to tropopause heights over IAWPR. Mechanisms that could cause such low temperatures over IAWPR are discussed. Intraseasonal oscillations with period of 30–40 days are observed in WVMR at various pressure levels. At 100 hPa level such oscillations are noted to be closely associated with similar oscillation in OLR and temperature. These observations suggest that variations in OLR (proxy of convection activity) produce such oscillation in WVMR. Present analysis thus report signature of convection in upward transport of WV, seasonal and intraseasonal oscillation in WVMR in upper troposphere and lower stratosphere (UTLS).► A signature of convection in upward transport of water vapor mixing ratio (WV) ► Seasonal variability of WVMR ► Intraseasonal oscillations with period of 30–40 days are observed in WVMR at various pressure levels.
Atmospheric Chemistry and Physics, 2015
In this study we examine the simulated downward transport and mixing of stratospheric air into the upper tropical troposphere as observed on a research flight during the SCOUT-O3 campaign in connection with a deep convective system. We use the Advanced Research Weather and Research Forecasting (WRF-ARW) model with a horizontal resolution of 333 m to examine this downward transport. The simulation reproduces the deep convective system, its timing and overshooting altitudes reasonably well compared to radar and aircraft observations. Passive tracers initialised at pre-storm times indicate the downward transport of air from the stratosphere to the upper troposphere as well as upward transport from the boundary layer into the cloud anvils and overshooting tops. For example, a passive ozone tracer (i.e. a tracer not undergoing chemical processing) shows an enhancement in the upper troposphere of up to about 30 ppbv locally in the cloud, while the in situ measurements show an increase of ...