Determination of cloud position in CERES products

[xwgw]

How to obtain cloud information in CERES 'product SYN1deg, because there is only cloud top height information, no cloud base height information, how to determine the position of the cloud? What is the effective height of the cloud and how is it defined?

[ASDC - cheyenne.e.land]

Hello,

Thank you for your interest in CERES data.

The cloud effective temperature of the cloud is the temperature returned from the Planck function using the observed imager radiance. The cloud effective height is the corresponding height you would find that temperature in the temperature profile. The cloud height is an adjustment to the effective cloud height based upon the cloud optical depth.

The cloud base pressure and temperature are provided which are used in the Fu-Liou radiative transfer calculations. You can get the cloud base height by using the hypsometric equation or by calculating a saturated adiabatic lapse rate at that point.

Regard,
ASDC

[xwgw]

Thank you very much for your answer. I am still a little confused, because I do not know how to calculate the saturated adiabatic lapse rate. Therefore, I would like to ask whether the geometric thickness of the cloud can be retrieved by using other micro-parameter information of the cloud (such as the effective radius of cloud particles, the visible thickness of cloud, etc.). Then, according to the difference between the height of the cloud top and the geometric thickness of the cloud, the height of the cloud base can be obtained (because the long-wave radiation is related to the height of the cloud base). Is there any specific literature or anything like that that has a specific method? In addition, I want to know that the long-wave radiation, that is, the difference in radiation flux between the total channel and the short-wave channel?

[xwgw]

What is the relationship between cloud effective temperature, cloud effective altitude, cloud effective pressure and cloud radiation? Is the effective temperature and height of the cloud information used to represent the temperature in the cloud and the geometric thickness of the cloud?

[ASDC - cheyenne.e.land]

Hello,

We contacted a member of the CERES Science team and they have stated:

CERES and the imager measurements are satellite based and they are measuring the radiation emitted near the top of the cloud. Therefore, the window channel imager radiance after having atmospheric corrections applied is used to obtain the cloud effective temperature using the inverse Plank function. The temperature, height, and pressure profiles from the Global Modeling and Assimilation Office are used to obtain the pressure and height that the retrieved effective temperature is located through linear interpolation.

I did locate the empirical relationship that is used to calculate cloud thickness in km used in our processing:

For water clouds with optical depth > 1: Cloud Thickness = 0.39 * ln(COD) - 0.1

optical depth <= 1: Cloud Thickness = 0.05 * SQRT(COD)

For ice clouds colder than 245 K: Cloud Thickness = 7.2 - 0.024 * Cloud Effective Temp + 0.95 * ln(COD)

The minimum cloud thickness is 0.02 km in either case.

The cloud thickness is subtracted from the cloud top height to get the cloud base.

The SYN1deg does not have broadband radiances due to the angular dependence involved. Also, most hours do not have CERES flux measurements, but values obtained from either narrowband to broadband fluxes based on geostationary imager radiance or interpolation. The radiance information is on the SSF or SSF1deg-Hour products.

The articles covering the cloud retrievals are

Minnis, P., S. Sun-Mack, Y. Chen, F. Chang, C. R. Yost, W. L. Smith, P. W. Heck, R. F. Arduini, S. T. Bedka, Y. Yi, G. Hong, Z. Jin, D. Painemal, R. Palikonda, B. R. Scarino, D. A. Spangenberg, R. A. Smith, Q. Z. Trepte, P. Yang, Y. Xie, 2020: CERES MODIS Cloud Product Retrievals for Edition 4–Part I: Algorithm Changes. IEEE Transactions on Geoscience and Remote Sensing, 1-37. doi: 10.1109/TGRS.2020.3008866

Minnis, P., S. Sun-Mack, D. Young, P. Heck, D. Garber, Y. Chen, D. Spangenberg, R. Arduini, Q. Trepte, W. Smith, J. Ayers, S. Gibson, W. Miller, G. Hong, V. Chakrapani, Y. Takano, K. Liou, Y. Xie, P. Yang, 2011: CERES Edition-2 Cloud Property Retrievals Using TRMM VIRS and Terra and Aqua MODIS Data #x2014;Part I: Algorithms. IEEE Transactions on Geoscience and Remote Sensing, 49(11), 4374-4400. doi: 10.1109/TGRS.2011.2144601.