Publication Abstracts

Wang 1997

Wang, J., 1997: Determination of Cloud Vertical Structure from Upper Air Observations and Its Effects on Atmospheric Circulation in a GCM. Ph.D. thesis. Columbia University.

The GISS GCM is used to investigate effects of macro-scale cloud vertical structure (CVS), including cloud base and top heights and layer thicknesses, and the characteristics of multi-layered clouds, on atmospheric circulations. Clouds suppress Hadley circulations in the transient state, but intensify them in the equilibrium state. The existence of multi-layered clouds is more important than top heights of the highest cloud layers for Hadley circulations. Vertical gradients of clouds are more important than their horizontal gradient for circulations. The results suggest the importance of cloud top radiative cooling and base warming within clouds for circulations and thus the requirement of resolving such structure for observations and GCMs. Clouds affect atmospheric circulations by directly modifying radiative cooling and directly imposing opposing effects on latent heating mainly through modulating atmospheric thermodynamics.

A method was developed to use rawinsonde humidity profiles to estimate cloud layer base and top locations based on the fact of high relative humidity (HRH) within clouds and sudden RH jumps at cloud boundaries. The analysis method has been applied in a 20-year (1976-1995) global daily rawinsonde dataset to create a 20-year global CVS dataset, and has been validated by comparing RAOBS-determined CVS properties with other independent data sources. RAOBS can sample all low and middle clouds and determine their boundaries accurately. However, RAOBS might oversample 10% of all clouds globally which might be clear moisture layers, and miss high and thin clouds by 5%.

Global and annual mean cloud top and base heights, layer thicknesses and separation distance between two consecutive multiple clouds layers are 4.26 km MSL, 2.87 km MSL, 1.39 and 2.1 km, respectively. Globally, multi-layered clouds occur 46% of the time and are predominatly two-layered. The lowest layer of multi-layered cloud systems is usually located in the atmospheric boundary layer. Clouds over ocean occur more frequently at low levels and are thinner, but are more often formed in multiple layers than clouds over land. Average cloud top and base heights decrease with latitudes in each hemisphere, and are higher in summer than in winter. Multi-layered clouds exist most frequently in the tropics but least in the subtropics, and there are more multi-layered clouds in summer than in winter. CVS also exhibits significant regional variations.

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BibTeX Citation

@phdthesis{wa06100c,
  author={Wang, J.},
  title={Determination of Cloud Vertical Structure from Upper Air Observations and Its Effects on Atmospheric Circulation in a GCM},
  year={1997},
  school={Columbia University},
  address={New York, N.Y.},
}

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RIS Citation

TY  - THES
ID  - wa06100c
AU  - Wang, J.
PY  - 1997
BT  - Determination of Cloud Vertical Structure from Upper Air Observations and Its Effects on Atmospheric Circulation in a GCM
PB  - Columbia University
CY  - New York, N.Y.
ER  -

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