樋口＠名古屋大です．
Yanai教授から宣伝（その２）です．
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UCLA TROPICAL METEOROLOGY NEWSLETTER No.43 (February 18, 2001)
Part 2
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----------------------- continued from Part 1-------------------------
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ABSTRACTS (Continued)
************************
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Entrainment, Rayleigh Friction, and Boundary Layer Winds over the Tropical
Pacific
----------------------------------------------------------------------------
Bjorn Stevens, Jianjun Duan, James C. McWilliams, Matthias Munnich
and J. David Neelin
Department of Atmospheric Sciences, University of California, Los Angeles
Los Angeles, California, U. S. A.
(Submitted to the Journal of Climate)
Winds over the tropical Pacific are interpreted using mixed-layer theory.
The theory --- which posits that the surface winds can be derived in
terms of a force balance between surface drag,
pressure-gradients, Coriolis forces and the vertical mixing of
momentum into the boundary layer (entrainment) --- is very successful
in predicting the seasonal climatology of the surface winds. The
model is also used as a basis for interpreting previous results. In
particular the model illustrates why, when the momentum flux
divergence is modeled as a Rayleigh damping, optimal damping
coefficients are anisotropic. A linear variant of the model, that
also incorporates entrainment but neglects the quadratic relation
between the wind-speed and the surface stress, is also found to
skillfully predict the surface winds. Overall the incorporation of
the entrainment effect is critical, indicating that the acceleration
of the near surface winds by momentum mixing with the free atmosphere
is a first-order effect that should not be neglected in simple models.
Physically this effect is one of resisting the turning of the winds.
In addition to improving the representation of the winds, it leads to
realistic representations of the divergence of the vector wind. If
the key parameters of the model (the entrainment rate and the boundary
layer depth) are assumed to have uniform climatological mean values
over the Pacific basin, optimal parameter values can be derived by
matching the model winds to the climatology. Such a procedure leads
to boundary layer depths between 300-400m and entrainment rates
slightly less than 1 cms\1. While these are somewhat smaller than one
might expect based on previous experiences, they should be interpreted
as effective values necessary to reproduce the surface winds. By
exploring the steady states of a somewhat more general model of the
boundary layer winds (the so-called $K$-profile parameterization), we
show that, in models that account for the vertical structure of the
wind-profiles, optimal estimates of $w_e$ and $h$ are larger and more
in accord with our expectations.
<http://www.atmos.ucla.edu/~bstevens/publications.html>
*************************************
Dr. Bjorn Stevens
Department of Atmospheric Sciences
University of California, Los Angeles
405 Hilgard Avenue
Los Angeles, CA 90095-1565, U.S.A.
E-mail: <bstevens@atmos.ucla.edu>
<http://www.atmos.ucla.edu/~bstevens>
<ftp://tule.atmos.ucla.edu/pub/bjorn>
*************************************
-------------------------------------------------------------------------
Convective Momentum Transport Observed during the TOGA COARE IOP. Part I:
General Features
-------------------------------------------------------------------------
Wen-wen Tung and Michio Yanai
Department of Atmospheric Sciences, University of California, Los Angeles,
Los Angeles, California, U. S. A.
(Submitted to the Journal of the Atmospheric Sciences)
ABSTRACT
The momentum budget residual, X = (X,Y), is estimated with the objectively
analyzed soundings taken during the TOGA-COARE Intensive Observing Period
(November 1992-February 1993) to study the effects of convective momentum
transport (CMT) over the western Pacific warm pool. The time series of X
and Y exhibit multi-scale temporal behavior, showing the modulations by the
Madden-Julian oscillation (MJO) and other disturbances. The power spectra
of X, Y, and ITBB (an index of convective activity) are remarkably similar,
showing peaks near 10, 4-5 and 2 days, and at the diurnal period,
suggesting a link between deep cumulus convection and the
acceleration/deceleration of the large-scale horizontal motion, via CMT
which is being modulated by atmospheric waves and tides. The temporal
behavior of X and Y can be described as fractals from 1/4 to ~ 20 and from
1/4 to ~ 16 days, respectively. Their fractal characteristics are reflected
in the very large standard deviations around the small IOP means. From the
analyses of the quantities uX/abs(u), vY/abs(v), and v.X, the vertical
distributions of the frictional force and dissipation (epsilon = -v.X) due
to subgrid-scale eddies are determined. The frictional force and
dissipation occupy a deep tropospheric layer from the surface to 300 hPa.
In addition, a concentration of large friction and dissipation exist in a
layer just below the tropopause, suggesting the significance of momentum
detrainment from the top of deep cumuli. The IOP-mean frictional
deceleration and dissipation in the lower troposphere are ~ 0.5-1.0 m s-1
day-1 and ~ 1.0x10-4 m2 s-3, respectively. The product of eddy momentum
flux with the large-scale vertical wind shear shows that the momentum
transport is, on the average, downgradient, i. e., kinetic energy is
transferred from the large-scale motion to convection and turbulence.
<http://uniblab.atmos.ucla.edu/tropic/CMT1/>
***************************************
Prof. Michio Yanai
Department of Atmospheric Sciences
University of California, Los Angeles
405 Hilgard Avenue
Los Angeles, CA 90095-1565, U.S.A.
E-mail: <yanai@atmos.ucla.edu>
<http://uniblab.atmos.ucla.edu/~yanai/>
***************************************
--------------------------------------------------------------------------------
--------------------------------------
Investigation of the Large-scale Atmospheric Moisture Field over the
Midwestern United States in Relation to Summer Precipitation. Part I:
Relationships between Moisture Budget Components on Different Time-Scales
--------------------------------------------------------------------------------
------------------------------------
Abraham Zangvil*, Diane H. Portis, and Peter J. Lamb**
*Meteorology Unit, Blaustein Institute for Desert Research, Ben Gurion
University of the Negev, Sede Boker, 84990, Israel
**Cooperative Institute for Mesoscale Meteorological Studies
The University of Oklahoma, Norman Oklahoma 73019, U.S.A.
(To appear in Journal of Climate)
ABSTRACT
Atmospheric moisture budget components are evaluated for a large
area (1.23 x 106 km2) in the Midwestern United States for all 12-hour
(12-00, 00-12 UT) and 24-hour (12-12 UT) periods during the contrasting
summers (May-August) of 1975, 1976, 1979, and 1988. The atmospheric
moisture flux divergence (MFD, separated into horizontal and vertical
advection components, HA and VA) and storage change (dPW) are estimated
using a standard finite difference method applied to objectively analyzed
U.S. and Canadian rawinsonde data (50 hPa vertical resolution, surface-300
hPa) for 00 and 12 UT. Area-averaged precipitation (P) totals are derived
from approximately 600 relatively evenly distributed (but ungridded)
recording raingauges. Evapotranspiration (E) is estimated as a residual of
the moisture budget equation and compares favorably with the few existing
observations, especially when totaled for periods of one month or longer.
Relationships between the budget components are established for the daily,
monthly, and seasonal time-scales using stratification, correlation, and
cross-spectral analyses.
On monthly and seasonal time-scales, the surface is a net source of
water vapor (positive E-P) and the bulk of this surplus is exported from
the region, largely through HA. For the daily budget, a threshold P rate
(~4 mm d-1) separates surplus E-P budgets from deficit budgets. On all
time-scales, most of the P variance is reflected in the VA component of
MFD, while HA explains ~80% of the variation in dPW. For the monthly and
(especially) daily budgets, E has bimodal distributions with P where the
minimum E occurs at P~2.6 mm d-1 (monthly) and P~4-5 mm d-1 (daily). For
drier daily P regimes, relatively high E is associated with increased
(decreased) dry VA (HA). The correlation of E with P becomes substantially
more positive from the daily-to-monthly time-scale, confirming the
importance of land-atmosphere interactions over longer periods. The above
stratification and correlation results are complemented by cross-spectral
analyses that identify strong associations between P-HA and P-dPW
previously masked by phase differences. The cross-spectral results also
prompt the development of a conceptual model that describes the temporal
relationships among the budget components for eastward moving large-scale,
"wave-like" disturbances with 3-10 day time-scales. The suggested sequence
of interactions is -- moist HA is accompanied by a pronounced PW increase
and then followed by a moist VA maximum; this horizontal and then vertical
moisture redistribution is first associated with an E minimum and then
culminates in a P maximum; after the P event, atmospheric drying occurs
through increased (diminished) dry HA (moist VA), which leads to an E
maximum and then P minimum.
************************************************
Prof. Abraham Zangvil
Institute for Desert Research
Ben Gurion University of the Negev
Sde Boker Campus, 84990
Phone: 972-7-6596845 (Work) 972-9-7679553 (Home)
Cell.: 972-5-2451004
Fax: 972-7-6596921 (Work) 972-9-7661437 (Home)
E-mail: <zangvil@bgumail.bgu.ac.il>
************************************************
---------------------------------------------------------------------------
The Monsoon as a Self-regulating Coupled Ocean-Atmosphere System
---------------------------------------------------------------------------
Peter J. Webster (1), Christina Clark (1), Galina Cherikova (1), John Fasullo
(1), Weiqing Han (1), Johannes Loschnigg (2), and Kamran Sahami (1)
(1) Program in Atmospheric and Oceanic Science,
University of Colorado, Boulder, Colorado
(2) International Pacific Research Center,
University of Hawaii, Honolulu, Hawaii
[In press: Meteorology at the Millenium (Ed. R. Pearce), Academic Press]
Abstract
Observational studies have shown that the Asian-Australasian monsoon
system exhibits variability over a wide-range of space and time scales.
These variations range from intraseasonal (20--40 days), annual,
biennial (about 2 years), longer term interannual (3--5 years) and
interdecadal. Despite this range of variability, the South Asian
monsoon (at least as described by Indian precipitation) exhibits a
smaller range of variability during its summer pluvial phase than
variability exhibited in other climate systems of the tropics. For
example, drought or flood rarely extend to multiple years, with rainfall
oscillating biennially from slightly above average to slightly below
average precipitation.
We argue that variability of the monsoon is regulated by negative
feedbacks between the ocean and the atmosphere. The annual cycle of the
heat balance of the Indian Ocean is such that there is an ocean heat
transport from the summer hemisphere from the summer hemisphere
resulting principally from wind-driven Ekman transport. Given the
configuration of the low-level monsoon winds, the Ekman transport is in
the opposite sense to the lower tropospheric divergent wind. The
cross-equatorial ocean heat transport is large with amplitudes varying
between +2 PW (northward) in winter and --2 PW (southward) in summer.
Thus, the wind-induced heat transport works to cool the summer
hemisphere upper ocean while warming the winter hemisphere. Similar
regulation occurs on interannual time scales. For example, during
anomalously strong northern hemisphere monsoon summers (typically a La
Nina), strong winds induce a stronger than average southward flux of
heat. When the monsoon is weak (typically an El Nino), the wind-driven
ocean heat flux is reduced. In this manner, the monsoon regulates itself
by reducing summer hemisphere sea-surface temperatures during strong
monsoon years and increasing it during weak years. In this manner, the
monsoon is self regulating.
It is noted, however, that the ocean heat transport theory of monsoon
regulation does not necessarily allow heat anomalies to persist from one
year to the next. Furthermore, the theory does not include the Indian
Ocean Zonal Mode (IOZM: sometinimes referred to as the Indian Ocean
dipole) as a dynamic entity. Finally, we develop a more general theory
in which the slow dynamics of the IOZM are integral components of a
sequence of processes that regulate the monsoon, thus minimizing radical
year to year departures of the monsoon from climatology.
******************************************
Prof. Peter J. Webster
Program in Atmospheric and Oceanic Science,
University of Colorado, Campus Box 311
Boulder, Colorado 80309, U. S. A.
<pjw@oz.colorado.edu>
******************************************
------------------------------------------------
The Tropical Western Hemisphere Warm Pool
------------------------------------------------
Chunzai Wang and David B. Enfield
Physical Oceanography Division
NOAA Atlantic Oceanographic and Meteorological Laboratory
Miami, Florida
Geophysical Research Letters (in press)
Abstract
The Western Hemisphere warm pool (WHWP) of water warmer
than 28.5C extends from the eastern North Pacific to the Gulf of
Mexico and the Caribbean, and at its peak, overlaps with the tropical
North Atlantic. It has a large seasonal cycle and its interannual
fluctuations of area and intensity are significant. Surface heat fluxes
warm the WHWP through the boreal spring to an annual maximum
of SST and areal extent in the late summer/early fall, associated with
eastern North Pacific and Atlantic hurricane activities and rainfall
from northern South America to the southern tier of the United
States. SST and area anomalies occur at high temperatures where
small changes can have a large impact on tropical convection.
Observations suggest that a positive ocean-atmosphere feedback
operating through longwave radiation and associated cloudiness is
responsible for the WHWP SST anomalies. Associated with an
increase in SST anomalies is a decrease in atmospheric sea level
pressure anomalies and an anomalous increase in atmospheric
convection and cloudiness. The increase in convective activity and
cloudiness results in less longwave radiation loss from the surface,
which then reinforces SST anomalies.
<http://www.aoml.noaa.gov/phod/docs.html>
*******************************************************************
* | *
* Dr. Chunzai Wang, Oceanographer | *
* NOAA/AOML/PhOD | Phone: 305-361-4325 *
* 4301 Rickenbacker Causeway | Fax: 305-361-4412 *
* Miami, FL 33149 | E-mail: wang@aoml.noaa.gov *
* | *
*******************************************************************
----------------------------------------------------------------------------
Dynamical and Cloud-Radiation Feedbacks in El Nino and Greenhouse Warming
----------------------------------------------------------------------------
F.-F. Jin
Department of Meteorology, SOEST, University of Hawaii at Manoa,
Honolulu, Hawaii
Z.-Z. Hu
Center for Ocean-Land-Atmosphere Studies,, Calverton, Maryland
M. Latif, L. Bengtsson & E. Roeckner
Max-Planck-Institut fur Meteorologie, Hamburg, Germany
(Geophys. Res. Lett., in Press)
Abstract:
An El Nino-like steady response is found in a greenhouse warming simulation
resulting from coupled ocean-atmosphere dynamical feedbacks similar to those
producing the present-day El Ninos. There is a strong negative cloud-radiation
feedback on the sea surface temperature (SST) anomaly associated with this
enhanced eastern equatorial Pacific warm pattern. However,this negative
feedback is overwhelmed by the positive dynamical feedbacks and cannot
diminish the sensitivity of the tropical SST to enhanced greenhouse gas
concentrations. The enhanced eastern-Pacific warming in the coupled
ocean-atmosphere system suggests that coupled dynamics can strengthen this
sensitivity.
****************************************
Dr. Zeng-Zhen Hu
Center for Ocean-Land-Atmosphere Studies
4041 Powder Mill Road, Suite 302
Calverton, MD 20705-3106 USA
Tel: 301-902-1270 Fax: 301-595-9793
Email: hu@cola.iges.org
****************************************
___________________________________________________________________________
************
IAMAS 2001
************
The Scientific Assembly of the International Association of Meteorology and
Atmospheric Sciences (IAMAS)
10-18 July 2001, Innsbruck, Austria.
<http://meteo.uibk.ac.at/IAMAS2001/>
The deadline for abstract (16 February 2001) has passed.
Next deadline: early registration 23 March 2001
-----------------------------
Selected Sessions of Interest:
-----------------------------
2.2 Modes of Current Climate Variability
3.1 Land-surface climate and interactions in global climate models
3.2 Snow cover and atmosphere interactions
4.3 Radiative Forcing and Climate Feedbacks
5.1 Clouds and Precipitation
6.1 Asian Monsoon and Global Climate
6.2 Monsoon Systems around the World
6.4 The Tropospheric Biennial Oscillation and Its Modelling
6.W Convective momentum transport (workshop: jointly with ICCP)
__________________________________________________________________________
***********************************************************************
UCLA TROPICAL METEOROLOGY NEWSLETTER is a forum for quick exchange of
information and discussions related to the "tropical" or "equatorial"
atmosphere and oceans (from the hydrosphere to the mesosphere) and
intends to cover all time and space scales. We invite news, reviews,
abstracts, Web-site updates, and comments/suggestions from the readers.
SEND YOUR CONTRIBUTION to Michio Yanai <yanai@atmos.ucla.edu>.
***********************************************************************
______________________________________________________________________
NEWSLETTERS AND PREVIEWS ON WEB:
*Previous issues of the UCLA TROPICAL METEOROLOGY NEWSLETTER PREVIEW
(from No. 10) are on the Web site of TOGA COARE Information Service
at the National Climatic Data Center (NCDC):
<http://www.ncdc.noaa.gov/coare/index.html>
(Look for "TOGA COARE community information" --->"updates").
*All previous issues of the NEWSLETTER (full text version) are on the Web site:
<http://uniblab.atmos.ucla.edu/tropic/newsletters>.
This Web site is maintained by Chih-Wen Hung <cw@atmos.ucla.edu>.
-----------------------------------------------------------------------------
Major contents of recent issues:
#40. Workshop on MJO and ENSO (GFDL 15-17 March 2000).
Harry Hendon (Climate Diagnostics Center, Boulder, Colorado)
<http://orca.rsmas.miami.edu/mjomip/mjo.enso.workshop>
#41. Correction of Humidity Data from the Vaisala RS80 Radiosondes during TOGA
COARE: Data Release.
Junhong Wang, Erik R. Miller, Harold L. Cole, David J. Carlson, and
Kathryn
Beierle (NCAR, Boulder, Colorado), and Ari Paukkunen (Vaisala OY,
Helsinki)
<http://www.atd.ucar.edu/homes/junhong/datarelease-nonATD.html>
#42. Superensemble Forecasts for Weather and Climate.
T.N. Krishnamurti Department of Meteorology. Florida State University
<tnk@io.met.fsu.edu>
--------------------------------------------------------------------------
FORTHCOMING ISSUES: Articles (Joanne Simpson; Peter Webster; Ed. Zipser;
and others). Abstracts (Yansen Wang, Wei-Kuo Tao, Joanne Simpson, and
Stephen Lang; Zhao-Xia Pu, Wei-Kuo Tao, Yiqin Jia, Joanne Simpson, Scott
A. Braun, Jeffrey Halverson, Arthur Hou, and William Olson; Yuko Okumura,
Shang-Ping Xie, Atusi Numaguti and Youichi Tanimoto; Kuan-Man Xu and David
A. Randall; Kuan-Man Xu, Richard T. Cederwall, Leo J. Donner, Wojciech W.
Grabowski,Francoise Guichard, Daniel E. Johnson, Marat Khairoutdinov,
Steven K. Krueger, Jon C. Petch, David A. Randall, Charles J. Seman,
Wei-Kuo Tao, Donghai Wang, Shao Cheng Xie, J. John Yio, and Ming-Hua
Zhang), Conference announcements, Web-site updates and more.
__________________________________________________________________________
To update the E-mailing list, please check below and return to the Editor.
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/**********************************************************************
樋口篤志 〒464-8601 名古屋市千種区不老町 名古屋大学大気水圏科学研究所
共同研究観測プロジェクトセンター Tel: 052-789-5467 Fax: 052-789-3449
e-mail: higu@ihas.nagoya-u.ac.jp (official)
ahiguchi@mui.biglobe.ne.jp (private use)
URL:http://rcwb.ihas.nagoya-u.ac.jp/~higu/
**********************************************************************/