SCM SCSMEX FORCING DATA

SCSMEX SESA (Southern Enhanced Sounding Array) averaged data fields

Version 3b-2 (released on 17 November 2004)

About the Dataset Files

Version 3b-2 (Vb2) of this dataset averages fields over the SESA polygon (see figure below) using version 3b of the upper air sounding data. Vb2 differs from Vb1 only in that the SESA domain is changed slightly to reduce the number of points within it that are over land. JMA analyses were used for all fields at the surface. Budget derived rainfall estimates were computed using JMA fluxes that were adjusted towards fluxes collected on the R/V Kexue 1 (at 6N, 110E) and processed by Dr. Parson's group at NCAR. Please report any suspicious looking features in these analyses to paulc@atmos.colostate.edu. The data are contained in the following four files:

basic fields as a function of pressure, fields.sesa

advection fields as a function of pressure, advect.sesa

heat and moisture fields as a function of pressure, q1q2.sesa

surface evaporation and budget-derived precipitation rates, eopo.sesa

To access these data files, click on the above hyperlinked filenames.

This figure shows an inventory of sounding data during the SCSMEX IOPs. A completely filled circle indicates that soundings were available 152 times out of a possible 152 (4 soundings per day for 38 days). The red circles indicate the nominal positions of the research vessels located within the enhanced sounding arrays.

Data in the above files represent an average of gridded data fields over the SCSMEX Southern Enhanced Sounding Array (SESA), that is, the southern polygon in the above figure. Fields of height (z), zonal wind (u), meridional wind (v), temperature (T) and specific humidity (q) were objectively analyzed using multiquadric interpolation (Nuss and Titley 1994) over a rectangular grid slightly larger than the SESA at 25 mb resolution from 1000 to 25 mb and at 1 degree resolution in both the latitude and longitude directions (see grid in above figure). Surface pressure was also analyzed over this grid. These analyses were done for 244 periods (61 days at 00, 06, 12, and 18 UTC) during May and June of 1998.

Data used in this analyses included quality-controlled sounding data from 43 sounding sites around and over the South China Sea and the JMA reanalysis around the borders of the analysis (every 5 degrees along 5S, 10N, 95E and 115 E), and at (9N,110E and Eq.,107E) if there were no observations within a 3 degree radius. During SCSMEX the ships were on site during the following periods:

IOP 1: 05/06/1998 to 05/25/1998 (20 days)
IOP 2: 06/05/1998 to 06/22/1998 (18 days)

Many of sounding sites over the Southern South China Sea (the SESA polygon) took observations 4x/day for the period from 05/05/98 thru 06/20/98. We refer to this 47-day period as the SCSMEX IOP during which time the results should be of higher quality due to the enhanced nature of the observations. This effect can be seen in the high correlation (0.85) between the Q2-budget derived rainfall and estimate from the TRMM 3B42 analyses during the 47-day IOP period. Outside of this IOP, there is little correlation between these two rainfall estimates.

Five-day filtered time series of rainfall estimates from the JMA/GAME reanalysis (dashed line), the TRMM 3B42 analysis (dotted line), and from the Q2 budget averaged (solid line) averaged over the SESA. Non-shaded region represents 47-day intensive observing period (IOP).

Notes:

For the surface analyses: data were assumed to be at the surface only if the height of the observations were within 10 m of the station height. Surface pressure represents pressure reduced to sea level.
Negative precipitation rates, found in the file "eopo.sesa" result from a combination of factors: sampling errors (i.e., the inadequacy of a sounding at a given time and location to represent conditions in a large area and a longer time period), data errors, errors introduced by the objective analyses, and errors in the estimation of surface evaporation.
Evaporation rates were obtained from the JMA reanalyis and were adjusted towards the point flux measurement from collected on the R/V Kexue 1.
To keep updated on any future problems, issues and/or changes to the data, users should register with Paul Ciesielski at paulc@atmos.colostate.edu.

fields.sesa
File "fields.sesa" contains 244 periods of six-hourly data. For each six hour period there are 42 lines of data.

Line 1 contains: [year, month, day, hour]
                  written with format (4i3)
Lines 2-42 contain: [p(mb), z(m), u(m/s), v(m/s), omega(mb/hr), T(C), 
                    theta(K), specific humidity(gr/kg) and 
                    divergence(1/s)*10e6] written with format (9f.2)

Omega is computed using O'Brien's (1970) method with an isovalue divergence adjustment. Omega is set to zero at the surface and at 100 mb.

advect.sesa
File "advect.sesa" contains 244 periods of six-hourly data. For each six hour period there are 42 lines of data.

Line 1 contains: [year, month, day, hour]
                 written with format (4i3)
Lines 2-42 contain: [p(mb), hu(m/s**2), vu(m/s**2), hv(m/s**2), vv(m/s**2),
                          hT(C/s), vT(C/s), hq(gr/(gr*s)), vq(gr/(gr*s))]
                          written with format (f8.2,1p,8e11.3)
                          where hu - horizontal advection of u
                          where vu -   vertical advection of u
                          where hv - horizontal advection of v
                          where vv -   vertical advection of v
                          where hT - horizontal advection of T
                          where vT -   vertical advection of T
                          where hq - horizontal advection of q
                          where vq -   vertical advection of q

These horizontal and vertical advection terms were computed using centered differences as follows:

horizontal advection of "f": h(f) = u*df/dx + v*df/dy
                      where: dx = a cos(phi)*d(lambda)
                             dy = a d(phi)
                             phi    - latitiude
                             lambda - longitude
vertical advection of "f": v(f) = omega*df/dp

q1q2.sesa
File "q1q2.sesa" contains 244 periods of six hourly data. The computation of Q1 and Q2 were not done for the first and last periods of the IOP because time center differences were used in computing these fields and no grids were analyzed before and after the IOP. For each six hour period there are 42 lines of data.

Line 1 contains: [year, month, day, hour]
                 written with format (4i3)
Lines 2-42 contain: [p(mb), Q1(C/day), Q2(C/day)]
                          written with format (3f.2)

The apparent heat source, Q1, and moisture sink, Q2 (Yanai et al. 1973) were computed as:

Q1/cp = [dT/dt + h(T) + (p/po)**kappa * omega * d(theta)/dp]
Q2/cp = -Lv/cp * [dq/dt + h(q) + v(q)]
      where dt = 12 hours
            po = 1000 mb
            cp = 1004
            Lv = 2.5e6
             g = 9.8

eopo.sesa
File "eopo.sesa" contains values of surface evaporation (e_0) and precipitation rates (p_0) for 244 six-hourly periods. The surface evaporation values represent the average from the JMA reanalyses. Once surface evaporation is known, rainfall rates can be computed from the moisture budget by integrating the equation for Q2 (shown above) from 1000 mb to 100 mb as follows:

p_0 = e_0 + 1./(g*Lv) * [integral(Q2*dp) from 1000mb to 100mb]

Line 1-244 contains: [year, month, day, hour, e_0(mm/day), p_0(mm/day)]
                     written with format (4i3,2f8.2)

References
Nuss W.A. and D.W. Titley, 1994: Use of multiquadric interpolation for meteorological objective analysis. Mon. Wea. Rev., 22, 1611-1631.

O'Brien J.J., 1970: Alternative solutions to the classical vertical velocity problem. J. Appl. Meteor., 9, 197-203.

Yanai, M.S., S. Esbensen and J.H. Chu, 1973: Determination of bulk properties of tropical cloud clusters form large-scale heat and moisture budgets. J. Atmos. Sci., 30, 611-627.

Please send any questions or comments to Paul Ciesielski, paulc@atmos.colostate.edu