The Iowa data set for the period 1972-1994, consists of soil moisture observations from two different catchments (W2 & W3), located at 41.2°N, 95.6°W in the southwestern part of the state. The data set is described in detail by Entin (1998), and have been used to study the scales of soil moisture variations (Entin et al., 1999). Each catchment has three sites where soil moisture observations were taken. Observations are available for 12 soil layers extending to a depth of 2.6 m. Details of each layer along with the technique used, are given in Table 1. For the first catchment the top four layers were measured using the gravimetric technique, and a neutron probe was used for the layers beneath 45.7 cm. For the second catchment, the gravimetric method was used for the top five layers and a neutron probe for the lower layers. Soil moisture was recorded in percent wetness by weight. Soil density observations are only available for those layers that were monitored gravimetrically. For the other layers soil density was estimated from observations from similar layer depths using other columns in the region. The record of observations begins in 1972 and continues until 1994, giving 23 years of record. For the most part, observations were made only between April and October, on average twice a month. Although observations were not taken at any fixed day of a month, they were always taken on the same day at all the six sites. Time series data corresponding to each individual layer are available for downloading in both GrADS and ASCII formats.

2. DATA SETS IN ASCII FORMAT

These data are archived in files Iowa.*.dat, where * is W2 or W3 corresponding to the two catchments. The numbers (1, 3, 4, 11, 14 and 16) together with W2 or W3 refer to observation points in the respective catchments. Following the header information, the data for the 12 levels (in inches) are written according to FORTRAN format

format(i4,x,i2,x,i2,x,i3,x,i5,6x,i2,12(x,f5.1)). 
(Year, month, day, day of year, day of record, site code, data)

A Fortran program reader.f, to read the data is also included in the directory containing the ASCII data. These data files can be downloaded by clicking here.

3. GrADS FILES

GrADS control and binary files consisting time series for Iowa can be also downloaded for visualization. These files are iowa.ctl and iowa.bdat and contain time-series for three stations in each of the two catchments. The variable names tr21, tr23, tr24, tr311, tr314, and tr316 correspond to the different catchments and locations. The z levels are the twelve soil layers for which the data are available. The layer thicknesses are in inches as in the ASCII data files and the soil moisture values are in percent weight.

4. REFERENCES

Entin, Jared K., Alan Robock, Konstantin Y. Vinnikov, Steven E. Hollinger, Suxia Liu, and A. Namkai, 2000: Temporal and spatial scales of observed soil moisture variations in the extratropics. J. Geophys. Res., 105, 11,865-11,877. ABSTRACT , PDF file. 

        Table 1. Soil layers observed and technique used at the two catchments
                in Iowa.  (1 inch = 2.54 cm)
        
        ------------------------------------------------------------------------------
        Layer   Layer Boundaries        Thickness of    Catchment W-2   Catchment W-3
          #         (in inches)         Layer (inches)
        ------------------------------------------------------------------------------
         
          1             0 -  3              3.0           Gravimetric    Gravimetric

          2             3 -  6              3.0           Gravimetric    Gravimetric    
        
          3             6 - 12              6.0           Gravimetric    Gravimetric

          4            12 - 18              6.0           Gravimetric    Gravimetric

          5            18 - 27              9.0           Neutron Probe  Gravimetric

          6            27 - 33              6.0           Neutron Probe  Neutron Probe

          7            33 - 42              9.0           Neutron Probe  Neutron Probe

          8            42 - 54             12.0           Neutron Probe  Neutron Probe

          9            54 - 66             12.0           Neutron Probe  Neutron Probe

         10            66 - 78             12.0           Neutron Probe  Neutron Probe

         11            78 - 90             12.0           Neutron Probe  Neutron Probe

         12            90 -102             12.0           Neutron Probe  Neutron Probe

        -------------------------------------------------------------------------------

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