NERC Data Catalogue Service
Daily MODIS (MODerate Imaging Spectroradiometer) derived cloud droplet number concentration global dataset for 2003-2015
Daily global cloud droplet number concentrations (Nd) have been calculated at 1x1 degree resolution from pixel-level MODIS (MODerate Imaging Spectroradiometer) Collection 5.1 Joint Level-2 (Aqua satellite) optical depth (tau) and the 3.7 micron effective radius (reff) data (and other supporting data) using the adiabatic cloud assumption (liquid water content increases linearly with height, Nd is constant throughout the cloud depth and the ratio of the volumne mean radius to the effective radius is assumed constant).
The Nd data is contained in separate NetCDF files for each year for the period 2003-2015. Nd is contained in the "Nd" variable and has units of cm^{-3}. This is a 360x180xNdays (lon x lat x Ndays) sized array, where Ndays is the number of days in the year. The lon x lat grid is a regular 1x1 degree grid. The time is provided as both a 1D array of size Ndays ("time") with units of days since 1st Jan, 1970 and an array of size Ndays x 3 ("time_vec") that contains numbers for the year month and day for each of the Ndays entries.
A number of filters have been applied to the data in order to remove retrievals that are likely to be problematic, or to violate the adiabatic cloud assumptions. Data is only included if:
1) Pixels are determined to be liquid pixels by MODIS.
2) The 1x1 degree mean cloud top height (calculated using the MODIS cloud top temperature and the sea surface temperature) is below 3.2km.
3) The 1x1 degree liquid cloud fraction was larger than 80%.
4) The 1x1 degree mean solar zenith angle was 65 degrees or less to avoid biases at high angles (Grosvenor and Wood, 2014).
Note, that the filtering is different to that described in Grosvenor, AMTD, 2018 in the following ways :-
1) 1km resolution tau and reff are used to calculate Nd, which is then aggregated to 1x1 degree resolution (rather than using 1x1 degree tau and reff).
2) Only Nd based on the 3.7 micron reff retrieval is provided here.
3) No filtering for the presence of sea-ice is done here - it is recommended that this is done if using for high latitudes.
4) The data here is not restricted to tau>5.
Also note that the vertical penetration bias correction described in Grosvenor, AMTD, 2018 is NOT applied here. In addition, as described in the latter paper, further pixel-level screening is performed in order to select high quality data.
Details on the reasons for restricting to low solar zenith angles can be found in Grosvenor and Wood, ACP, 2014. Information on the pixel level filtering applied can be found in Grosvenor et al., AMTD, 2018 (noting the differences explained above). A comparison of this dataset with others can be found in Grosvenor et al., Reviews of Geophysics, 2018.
This dataset calculates a product that is not provided as standard by MODIS. It uses improved optical depth and effective radius data compared to the standard MODIS Level-3 data since situations (e.g., high solar zenith angles, broken clouds) that have been shown to cause retrieval issues have been filtered out at the Level-2 stage before being averaged into Level-3 droplet concentration data.
Default
Identification info
- Metadata Language
- English (en)
- Dataset Reference Date ()
- 2018-05-23T15:54:22
- Dataset Reference Date ()
- 2018-05-23T15:54:22
- Identifier
- Centre for Environmental Data Analysis (CEDA) / cf97ccc802d348ec8a3b6f2995dfbbff
- Maintenance and update frequency
- notPlanned
- Update scope
- dataset
- Keywords
-
- Not defined
- GEMET - INSPIRE themes, version 1.0 ()
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- atmospheric conditions
- Limitations on Public Access
- otherRestrictions
- Other constraints
- Public data: access to these data is available to both registered and non-registered users.
- Use constraints
- otherRestrictions
- Spatial representation type
- grid
- Topic category
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- Climatology, meteorology, atmosphere
))
- Begin date
- 2003-01-01T00:00:00
- End date
- 2015-12-31T23:59:59
- Code
- WGS 84
Distribution Information
- Data format
-
-
NetCDF
()
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NetCDF
()
- Resource Locator
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CEDA Data Catalogue Page
Detail and access information for the resource
- Resource Locator
-
DOWNLOAD
Download Data
- Resource Locator
-
Grosvenor, D. P., and R. Wood (2014), The effect of solar zenith angle on MODIS cloud optical and microphysical retrievals within marine liquid water clouds, Atmos. Chem. Phys., 14, 7291–7321, doi:10.5194/acp-14-7291-2014.
No further details.
- Resource Locator
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Grosvenor, D. P., O. Sourdeval, and R. Wood (2018), Quantifying and correcting the effect of vertical penetration assumptions on droplet concentration retrievals from passive satellite instruments, Atmospheric Measurement Techniques Discussions, 2018, 1–21, doi:10.5194/amt-2017-477.
No further details.
- Resource Locator
-
CEDA Data Catalogue Page
Detail and access information for the resource
- Resource Locator
-
DOWNLOAD
Download Data
- Resource Locator
-
Grosvenor, D. P., and R. Wood (2014), The effect of solar zenith angle on MODIS cloud optical and microphysical retrievals within marine liquid water clouds, Atmos. Chem. Phys., 14, 7291–7321, doi:10.5194/acp-14-7291-2014.
No further details.
- Resource Locator
-
Grosvenor, D. P., O. Sourdeval, and R. Wood (2018), Quantifying and correcting the effect of vertical penetration assumptions on droplet concentration retrievals from passive satellite instruments, Atmospheric Measurement Techniques Discussions, 2018, 1–21, doi:10.5194/amt-2017-477.
No further details.
- Quality Scope
- dataset
Report
- Dataset Reference Date ()
- 2010-12-08
- Statement
- The data upon which this dataset was based was downloaded in the form of Collection 5.1 Joint Level-2 cloud product swaths (MYDATML files) from the MODIS-Aqua satellite instrument via the MODIS FTP service. They were then processed using Matlab following the methods described above onto a regular 1x1 degree grid with separate values stored for each overpass of a given gridbox. Overpasseses with a solar zenith angles larger than 65 degrees were not included in the subsequent averaging to daily values.
Metadata
- File identifier
- cf97ccc802d348ec8a3b6f2995dfbbff XML
- Metadata Language
- English (en)
- Character set
- 8-bit variable size UCS Transfer Format, based on ISO/IEC 10646
- Parent identifier
- National Centre for Earth Observation (NCEO) Third Party Data 3b0630c7fa264164868d4da5c9f90bed
- Resource type
- dataset
- Metadata Date
- 2024-08-22T23:03:39
- Metadata standard name
- UK GEMINI
- Metadata standard version
- 2.3
