Identification

Title

Diurnal patterns of rainfall in northwestern South America. Part III: Diurnal gravity waves and nocturnal convection offshore

Abstract

Afternoon/evening near-coastal convection over land is easily understood as a response to solar heating of the land, turbulent transfer of heat and moisture to the boundary layer, and lifting of air by vigorous sea-breeze fronts. Subtler processes apparently underlie the late night and morning convection that is prevalent over coastal waters throughout the Tropics. Sensitivity tests using the fifth-generation Pennsylvania State University-NCAR Mesoscale Model (MM5), and further diagnoses of the control run described in Part II, are used to explore these processes. Prior studies have speculated that "land-breeze" circulations, analogous but opposite to the sea breeze, drive offshore convection at night. However, nighttime radiative cooling of land and the associated thermal breezes are much weaker than the corresponding daytime processes, especially under humid tropical skies. Analysis of model mean soundings reveals that modest (fractions of a degree Celsius) temperature changes near the 800-hPa level change the sign of the buoyancy of low-level air, from negative (inhibited) to positive (convecting) after about midnight in the coastal zone. These diurnal temperature changes are seen to be signatures of a diurnal gravity wave with a propagation speed of ~15 m s⁻¹, similar to the speed of motion of the diurnal seaward sweep of convection seen in satellite data as well as in the model. This wave radiates from the diurnally oscillating heat source of the daytime mixed layer, raised up into the stratified layers of the atmosphere by elevated terrain. A surprising finding is that the model mean rainfall field is almost the same in a simulation without diurnally varying solar radiation.

Resource type

document

Resource locator

Unique resource identifier

code

https://n2t.org/ark:/85065/d7542pwr

codeSpace

Dataset language

eng

Spatial reference system

code identifying the spatial reference system

Classification of spatial data and services

Topic category

geoscientificInformation

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keyword value

Text

originating controlled vocabulary

title

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reference date

date type

publication

effective date

2016-01-01T00:00:00Z

Geographic location

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East bounding longitude

North bounding latitude

South bounding latitude

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End position

Dataset reference date

date type

publication

effective date

2003-05-01T00:00:00Z

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Use constraints

Copyright 2003 American Meteorological Society (AMS). Permission to use figures, tables, and brief excerpts from this work in scientific and educational works is hereby granted provided that the source is acknowledged. Any use of material in this work that is determined to be "fair use" under Section 107 of the U.S. Copyright Act or that satisfies the conditions specified in Section 108 of the U.S. Copyright Act (17 USC §108, as revised by P.L. 94-553) does not require the AMS's permission. Republication, systematic reproduction, posting in electronic form on servers, or other uses of this material, except as exempted by the above statement, requires written permission or a license form the AMS. Additional details are provided in the AMS Copyright Policy, available on the AMS Web site located at (http://www.ametsoc.org/AMS) or from the AMS at 617-227-2425 or copyright@ametsoc.org.

Limitations on public access

None

Responsible organisations

Responsible party

contact position

OpenSky Support

organisation name

UCAR/NCAR - Library

full postal address

PO Box 3000

Boulder

80307-3000

email address

opensky@ucar.edu

web address

http://opensky.ucar.edu/

name: homepage

responsible party role

pointOfContact

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