Diabatic Heating and Cooling Rates Derived from In Situ Microphysics Measurements: A Case Study of a Wintertime U.K. Cold Front

Abstract

In situ measurements associated with the passage of a kata cold front over the United Kingdom on 29 November 2011 are used to initialize a Lagrangian parcel model for the purpose of calculating rates of diabatic heating and cooling associated with the phase changes of water within the cloud system. The parcel model calculations are performed with both bin-resolved and bulk treatments of microphysical processes. The in situ data from this case study reveal droplet number concentrations up to 100 cm 23 , with planar ice crystals detected at cloud top, as well as columnar crystals produced by rime splinter ejection within the prefrontal warm sector. The results show that in terms of magnitude, the most significant rates of diabatic heating and cooling are produced by condensation growth of liquid water within the convective updrafts at the leading edge of the front. The peak temperature tendencies associated with condensation are typically found to be at least an order of magnitude larger than those associated with the ice phase, although the cooling effect from sublimation and melting occurs over a wide region. The parcel model framework is used in conjunction with the observations to assess the suitability of existing bulk microphysical treatments, of the kind used in operational weather forecast models. It is found that the assumption of spherical ice crystals (with diameters equal to the maximum dimension of those sampled), along with the use of negative exponential functions to describe ice particle size distributions, can lead to an overestimation of local diabatic heating and cooling rates by a factor of 2 or more.Denotes Open Access content.

Observations of the Origin and Distribution of Ice in Cold, Warm, and Occluded Frontal Systems during the DIAMET Campaign

“…The ice particles generated in this temperature zone dominate the ice crystal number concentration throughout the depth of the cloud. Further details of the cloud ice spectra and their parameterization in models together with detailed modeling of the diabatic processes in this case may be found in the companion paper Dearden et al (2014). 8b) show that the highest contribution to the ice water content occurred at ;3 km, where higher concentrations of ice crystals were observed than in any other region of the cloud system.…”

“…Kata cold fronts are the result of dry air intrusions, characterized by a region of air descending from the tropopause region that can overrun the surface front (Browning 1997). The reader is referred to Dearden et al (2014) for a consideration of diabatic heating and cooling rates derived from some of the microphysics data that will be presented here. It also leads to forward motion of the air above the warm conveyor belt relative to the movement of the cold front.…”

The non‐conservation of potential vorticity by a dynamical core compared with the effects of parametrized physical processes

“…This period corresponds to a case‐study from the DIAMET (DIAbatic influences on Mesoscale structures in ExTratropical storms) project (Vaughan et al , ) of a double cold front passing over the UK. Diabatic heating and cooling rates in the cold front due to phase changes of water were investigated by Dearden et al () using insitu flight data for this case‐study. More in‐depth details of the meteorological conditions during the case‐study are given in Dearden et al ().…”

“…Diabatic heating and cooling rates in the cold front due to phase changes of water were investigated by Dearden et al () using insitu flight data for this case‐study. More in‐depth details of the meteorological conditions during the case‐study are given in Dearden et al ().…”

Cloud Banding and Winds in Intense European Cyclones: Results from the DIAMET Project

“…One of the main objectives of DIAMET was to quantify diabatic heating and cooling rates using the observed microphysics, to compare with and improve model simulations. As an example of this, the method described in Dearden et al (2014) has been used to calculate instantaneous diabatic heating and cooling rates associated with the growth and evaporation of ice crystals by vapor diffusion along this section of the flight (Fig. 8e).…”