Note: All files are referred to are in the UW anonymous ftp archive, and are identified relative to the path pub/astex/lagr on anonymous ftp on atmos.washington.edu. Click here to download Lagrangian data files from this archive.
The two ASTEX Lagrangian experiments were comprehensive studies of the evolution of a boundary layer airmass over roughly 36 hour periods. In each Lagrangian, aircraft observations were taken an continuously as possible following the mean motion of the air in the marine boundary layer (MBL). The information in this directory is mainly oriented toward providing an effective comparison of the two ASTEX Lagrangian experiments with column models of the cloud-topped marine boundary layer. The data presented here are discussed in three papers, the first two of which are available via anonymous ftp (see README for parent directory ASTEX for more information). The papers discussing the data are: I Bretherton, C. S. and R. Pincus, 1995: Cloudiness and Marine Boundary Layer Dynamics in the ASTEX Lagrangian Experiments. Part I: Synoptic setting and vertical structure. J. Atmos. Sci., 52, 2707-2723 II Bretherton, C. S., P. A. Austin and S. T. Siems, 1995: Cloudiness and Marine Boundary Layer Dynamics in the ASTEX Lagrangian Experiments. Part II: Cloudiness, drizzle, surface fluxes and entrainment. J. Atmos. Sci., 52, 2724-2735. III Austin, P. A., and C. S. Bretherton, 1995: Broadband radiative fluxes during the ASTEX Lagrangian experiments. Available from Phil Austin as a UBC tech report. The hourly data for the two Lagrangians are in the subdirectory /hourly of /lagr1 and /lagr2, respectively. The /hourly subdirectory contains a a subdirectory /ECMWF (described below), a file named 'scalars', and a set of files named 'lagr[n]_h[mm]' containing hourly composite soundings for the periods: 16 UTC 12 June-10 UTC 14 June, 1992 for Lagr. 1 22 UTC 18 June-14 UTC 20 June, 1992 for Lagr. 2 In the hourly file name, [n] = 1 or 2 is the Lagrangian number, and [mm] is the hour number, starting from 00 at the first hour. Each file has a header with hourly interpolated values of: June day decimal day of June lat, lon trajectory 'best guess' latitude (N) and longitude (W) [I] SST best fit SST (K) [II, figs. 1a and 1b] psurf surface pressure (hPa) [II, fig 2] Div avg. horizontal divergence over the MBL depth (10^-6 s^-1) [II,section 3d]. Mean vertical velocity = -D*z in the MBL. LW_dn downwelling broadband longwave flux at 700 hPa (W/m^2) [III, table 1]. To adjust this observation to a different pressure p, add 0.4*(p - 700) W/m^2. Except for days 19.45- 19.7, the downgoing longwave flux above the inversion closely approximates the clear sky value obtained from the ECMWF column sounding (which is used for the sounding at pressures less than 700 mb). On days 19.45-19.7, overlying cirrus raised the downgoing longwave flux by about 50 W/m^2. N Mean in-cloud droplet concentration (cm^-3) derived by hourly interpolation from the in- cloud segments of horizontal legs in which 30% or more of the leg was in-cloud [II,fig. 5]. This N is based on measurements entirely inde- pendent of the N's tabulated in the soundings. Together with the sounding information, the header information in each hourly file is sufficient to completely specify boundary conditions and initial conditions for a Lagrangian column model of the marine boundary layer started at an arbitrary hour into either Lagrangian. The file 'scalars' tabulates the hourly values of the above quantities for the entire Lagrangian, along with the inversion-base pressure pib (hPa) for each hour. In each hourly file, after the header follows a composite sounding with 50-100 mb resolution from 100 mb-700 mb and 10 mb resolution from 700 mb down to the surface. The columns ug and vg are the geostrophic wind components interpolated from ECMWF height fields, qv and ql are water vapor and liquid water mixing ratios and N is the mean droplet concentration. The remaining variables are standard. Note that unlike in the header, the N tabulated in the sounding is an average over both cloudy and non-cloudy segments of several aircraft soundings. If N exceeds 50% of the mean in-cloud drop concentration given in the sounding header, it is a fair guess that most of the average is over cloud. In addition, qv may not match the saturation mixing ratio even in mainly cloudy segments due to small measurement biases, cloud holes, etc. For using a composite sounding to initialize a model run, I recommend that you replace the vapor mixing ratio by the saturation mixing ratio wherever either N exceeds 50% of the mean in-cloud drop concentration, or ql exceeds 0.05 g/kg. Note also that since the geostrophic winds are from a large-scale analysis, they may have significant errors and are not always entirely consistent with the observed wind field. Caveat emptor! The hourly soundings were derived as follows: (i) From each of the 17 2mb averaged aircraft soundings in each Lagrangian, a corresponded blended sounding was constructed by assuming: (a) Between the lowest sounding pressure and the surface pressure (anywhere from 1-5 mb higher), theta, qv, u, v are uniform and equal to the lowest sounding value. (b) More than 50 mb above the sounding top, and everywhere above 700 mb, ECMWF data interpolated to the sounding time and position are used. (c) At the sounding top, the difference of the aircraft and ECMWF data is found. Between 0 and 50 mb above the sounding top, this difference is linearly ramped to zero and added to the ECMWF data. (d) Geostrophic winds from ECMWF height fields are tabulated at all pressures (e) A column itype is included in the sounding which indicates the type of data used at each pressure: 1 - aircraft 2 - aircraft, with ECMWF winds (soundings 9,10 of Lagr. 1 only) 3 - ECMWF 4 - Ramped between ECMWF and aircraft 5 - Extrapolated below lowest aircraft level The 2mb aircraft and blended soundings can be found in subdirectories soundings/2mb and soundings/blended of /lagr1 and /lagr2. (ii) From the blended soundings, an hourly composite sounding was created by using a weighted average of all aircraft soundings within 3 hours of the compositing time. Soundings more than 3 hours away were used if necessary to make a temporally unbiased average. The compositing was done so as to preserve the inversion sharpness by vertically scaling each sounding to have the same inversion base height and surface pressure. A different scaling is used above the inversion base to bring the scaled pressure back to its true value at 700 mb for each blended sounding. The subdirectory /ECMWF should not be necessary to look at, but includes plevels.ec List of the 21 pressure levels for the ECMWF-derived (.ec) fields, which run from 1010 hPa to 100 hPa. ug.ec, vg.ec, t.ec, q.ec, u.ec, v.ec The hourly ECMWF theta (K), qv (g/kg), u, v, ug, vg (m/s). Each field is stored in order of increasing hour, with each of the 21 pressure levels in plevels.ec given sequentially for each hour. Written in (f7.2,9f8.2) format with 10 values per row. Model Verification The following data in lagr/lagr[n] may be useful for model verification: (1) The hourly composite soundings within the boundary layer. (2) The drizzle and cloud fraction data in the subdirectory leg_means. Other data such as turbulence profiles have been analyzed by other investigators. We hope to add such data to this archive if possible. If you have a dataset for the Lagrangians that might be useful for comparison with dynamical or chemical column models of the MBL, and if you would like to add your dataset to this archive, send email to Chris Bretherton at breth@atmos.washington.edu.
Lagrangian 1 trajectory, theta, qv, ql, N, u and v, ug and vg.
Lagrangian 2 trajectory, theta, qv, ql, N, u and v, ug and vg.
Figures 1a and 1b of paper II are a plot of SST for Lagrangians 1 and 2, respectively. The four data sources are tabulated in anonymous ftp in lagr[n]/sst and discussed in README.sst. Each data source has been corrected for assumed biases, and is plotted along with the best fit SST used in the hourly dataset.
Figure 4 of paper II is a plot of the cloud fraction derived from FSSP in-situ measurements and upward pointing PRT5 Electra radiomenter measurements. Satellite derived cloud fraction (fig 10 of paper I) also is included for comparison.
Figure 5 of paper II is a plot of the in-cloud average droplet concentration from horizontal aircraft legs with at least 30% of leg in cloud
Figures 6 and 7 of II are plots of drizzle rate and drizzle fraction for the two Lagrangians.
