Engineering topics

Vaughan, Geraint

Publications and source records attributed to Vaughan, Geraint.

4 records

NASA NTRS2008

Cloud-Resolved Simulations of Lightning NOx in an Observed Hector Thunderstorm

Cloud chemistry simulations are being performed for a "Hector" storm observed on 16 November 2005 during the SCOUT-03lACTIVE campaigns based in Darwin, Australia. The primary objective of these simulations is to estimate the average production of NO per lightning flash during the storm. The 3-D WRF-AqChem model is being used for these calculations. This modeling package contains the WRF nonhydrostatic cloud-resolving model, online gas- and aqueous-phase chemistry, and a lightning algorithm (Barth et al., 2007). Early morning soundings of temperature, water vapor and winds are used to initialize the model. Surface heating of the Tiwi Islands is simulated in the model to induce convection. Observations from the Egrett, Falcon, Geophysica, and Dornier aircraft in air undisturbed by the storm are used to construct composite initial condition chemical profiles. Convective transport in the model is tested using tracer species such as CO and O3. Lightning flashes observed by the LINET network are input to the model and a lightning placement scheme is used to inject the resulting NO into the simulated cloud. Various scenarios of NO production per flash are used for cloud-to-ground and intracloud flashes in a series of simulations for the storm. Resulting NO, mixing ratios from each simulation are compared with upper tropospheric anvil observations (from the Geophysica and Egrett aircraft) to determine the best fit with the mean NOx at anvil altitudes, the profile shape, and the frequency distribution of NOx values. We will compare the results for lightning NO production from this tropical thunderstorm with similar analyses conducted for several midlatitude and subtropical convective events.

Pickering, Kenneth↗

NASA NTRS1994

Ozone laminae near the edge of the stratospheric polar vortex

Analysis of ozonesonde data collected at high northern latitudes in winter and spring shows that laminae of enhanced and depleted ozone are associated with the polar vortex. In January and February, they are most common at all latitudes in the potential temperature range 370-430 K, but are abundant up to 500 K between 60 and 70 deg N. In March and April they occur most frequently northward of 75 deg N, and are abundant up to 520 K, whereas they are largely confined to the range 320-440 K at lower latitudes. Analysis of ozone lidar data obtained during AASE-1 depicts clearly the extrusion of laminae of enhanced ozone concentration from the polar regions in the altitude range 13-15 km. These extrusions form a class of laminae which transport ozone equatorward in the lowest levels of the stratosphere.

Reid, S. J.↗

NASA NTRS1994

Ozone and NO2 measurements from Aberystwyth and Lerwick

Measurements of the total column of ozone and NO2 were obtained by a SAOZ UV/Visible spectrometer at Aberystwyth (52.4 deg N, 4.1 deg W) and Lerwick (60.1 deg N, 1.2 deg W) during the period March 1991 - April 1992. NO2 measurements show a marked decrease in 1992 compared with 1991, due to the effect of aerosols from Mt. Pinatubo. Ozone measurements appear to have been affected by the aerosols - comparisons with both Dobson and TOMS measurements are presented.

Bartlett, L. M.↗

NASA NTRS1994

Detection of stratosphere troposphere exchange in cut-off low systems

The Aberystwyth MST radar has been used as part of the TOASTE program to study the structure of the tropopause in cut-off-low system with an aim to identifying regions where stratosphere-troposphere exchange are taking place. Theory predicts that the vertical gradient in reflected power is proportional to the static stability of the reflecting region, and should therefore resolve tropopause structure. Comparisons of MST power profiles with radiosonde data are presented and show good agreement, revealing regions of indefinite tropopauses, where stratosphere-troposphere exchange is thought to take place. The continuous nature of MST data allows an estimation of the size of these regions.

Price, Jeremy D.↗