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\begin{document}
\twocolumn[
\begin{center}
 {\large \bf 
        Experimental Study of General Circulations \\
        with the Parameters Relevant to Earth: \\
        General Circulations on an Aqua-Planet
        \vspace{1em}
        }

 {\large
        ${}^{*}$Yoshi-Yuki Hayashi$^{1}$,
        Shin-ichi Takehiro$^{2}$,
        Kensuke Nakajima$^{2}$, \\
        Masahiro Hosaka$^{3}$, and
        Masaki Ishiwatari$^{4}$
  }
        (${}^{*}$Contact Person)
 
 {\it 
        ${}^{1}$Grad. School of Math. Sci., Univ. of Tokyo, 
                Komaba 3-8-1, Meguro-ku, Tokyo, 153-8914, Japan \\
                and 
                Grad. School of Sci., Hokkaido Univ.,
                Kita 10 Nishi 8, Sappro, 060-0810, Japan

        ${}^{2}$Faculty of Science, Kyushu Univ. 
                Hakozaki 6-10-1, Fukuoka, 812-81, Japan 

        ${}^{3}$Meteofrolgical Research Institute,
                Japan Met. Agency,
                Nagamine 1-1, Tsukuba, 305-0052, Japan

        ${}^{4}$Grad. School of Env. Earth Science, 
                Hokkaido Univ., 
                Kita 10 Nishi 5, Sappro, 060-0810, Japan
  }

  \begin{quote}
    \begin{center}
    {\large \bf Abstract}
    \end{center}    

    {\bf 
    ``Aqua planet'' experiments are performed in order to investigate 
        the effects of an equatorial warm sea surface temperature
        (SST) area on the tropical large-scale precipitation patterns. 
    The warm SST area is placed at the equator 
        of an hypothetical aqua planet 
        whose SST distribution is zonally uniform and 
        symmetric about the equator. 

    The calculated tropical precipitation distributions
        are characterized by the appearance of an east-west asymmetry;
        precipitation decreases to the west of the warm SST area, 
        while it increases in the longitudinally wide area to the east.
    In the western region to the warm SST area,
        an increase of the stability 
        due to a temperature rise in the middle layer 
        is observed 
        and 
        correspondingly downward flow is recognized.
    In the eastern region,
        although a temperature rise appears in the middle layer,
        the stability decreases
        due to the increase of water vapor in the lower layer
        caused by the meridional moisture convergence.
   Experiments 
      in which the wind velocity used in the evaluation of the surface
      evaporation is fixed 
      are performed to show that 
      WISHE (Wind Induced Surface Heat Exchange)
      mechanism is not a principal cause for
      the generation of the east-west asymmetry of the 
      precipitation pattern. 

    The appearance of the decrease of precipitation 
        to the wet of the warm SST area may explain the occurrence of 
        drought over the Indonesian region during the El Nino
        events.  
}
        \vspace{1em}

  {\tenbfs 
  Keywords: Aqua planet,
            Warm SST anomaly,
            Equatorial precipitation,
            WISHE,
            ENSO}
  \end{quote}



\end{center}
]
\footnotetext[1]{E-mail address: shosuke@gfd-dennou.org}



\noindent
{\bf Background}
\vspace*{0.5em}

The grand purpose of our study is to reveal the dynamical structures 
which underlie the general circulations of the earth and 
planetary atmospheres. 
It is aimed to construct a theoretical framework which 
is useful in describing their circulation characteristics, as tried
by Golitsyn (1970). 
Through these activities, 
our interest is to recognize the atmosphere of the earth 
(or the climate of the earth) 
as one of the possible realizations in 
the physical parameter space observed in the solar system. 

One of our procedures in revealing the possible underlying
dynamics is to gather and classify atmospheric circulation patterns
which might be observed under various values of planetary ``external''
conditions such as orbital parameters (amount and variation of the
incoming solar flux), radius and rotation rate of the planet,
radiation property of the atmosphere, and surface boundary setups.
The sampling of the possible atmospheric circulations is 
to a certain extent possible by numerical experiments 
by the use of the super computer powers. 

Our search in circulation patterns is now performed for the following
three major activities:
\begin{enumerate}
\item to reveal the possible circulations which might be
      realized with the values of solar flux and orbital parameters 
      which are related to Mars, Earth and Venus,
\item to reveal the possible circulations which might be
      realized with the earth's condition, but with strongly
      simplified surface and/or physical processes, 
\item to reveal the possible circulations which might be
      realized as convection of a spherical shell in general.
\end{enumerate}
These are being studied continuously from the preceding
years by our research group. 

The present study belongs to the second activity listed above. 
The hypothetical earth utilized in this study is 
so called aqua-planet, where all
of the earth's surface is assumed to be covered by the
ocean (Hayashi and Sumi, 1986; Numaguti and Hayashi, 1991a, b; 
Numaguti, 1993).  
The aim is to answer the basic problem of the
climate, that is, ``where and how does it rain?''.  
In the aqua-planet experiments performed so far, 
the focus has been placed on especially 
in searching for the idealistic precipitation distribution of the
tropics.  
The experiment performed here is also in this category,
however, the new feature is to find out the deformation of the
precipitation distribution to a warm SST (sea surface temperature)
anomaly placed in the tropics.  
The configuration is supposed to
extract the effect of the warm SST region in the real Western Pacific
on the general circulation patterns.

We will show here 
      the precipitation patterns 
      over the entire tropical region 
      caused by a local warm SST area 
      placed at the equator of an aqua planet. 
    On the warm SST area, 
      an intense precipitation activity, so called, 
      convection center, will emerge. 
    However, 
      we will consider 
      the precipitation patterns all over the tropical region 
      affected by the existence of the convection center;
      we will not focus on the convection center itself.
    The SST distribution outside the warm SST area is zonally 
      uniform and symmetric about the equator
      to minimize the in situ effect on the precipitation
      properties. 
    
If we can neglect the various feedback mechanisms 
       in the moist atmosphere, 
       the precipitation patterns outside the convection center 
       will be easily predicted. 
The downward motion should be observed in the neighborhood of
       the convection center, 
       which should suppress precipitation there.
However, we know that 
      it is incomplete to predict the precipitation patterns
      without considering the water vapor supply and its transport. 
In the following results obtained by the numerical experiments, 
        it is actually shown 
        that precipitation decreases to the west of the convection center,
        but it increases to the east
        (Hosaka {\it et al.}, 1998). 

%
%---------------------------------------------------------------------
%

\vspace*{1em}
\noindent
{\bf Model} 
\vspace*{0.5em}

   The model used in this study is AGCM5 of GFD Dennou Club edition, 
      which is the three-dimensional primitive system on a 
      sphere (Swamp Project, 1998).
    The model is basically the same as that developed by and 
        used in Numaguti (1993). 
    The dynamical part is represented by the pseudo spectral method
      with the triangular truncation at wavenumber 42 (T42) and 
      by the sigma vertical coordinate with 16 vertical levels. 

   The model contains the following simplified physical processes.
   The employed cumulus parameterization is
      the Kuo scheme or the adjustment scheme.
    The condensed water is removed from the system 
      immediately after condensation and hence there are no clouds.
    The absorption and scattering of the solar radiation are not included.
    The longwave absorption is represented by four spectral bands, 
      three of which are of water vapor and 
      one is of dry air. 
    The scattering of the longwave radiation is not included.
    The absorption coefficients of the longwave radiation are 
      chosen 
      so that the cooling profile of the atmosphere 
      roughly resembles the observed one.
    The vertical turbulent mixing is represented by 
      the level II scheme of Mellor and Yamada.
    The surface fluxes of momentum, heat and water vapor are
      evaluated by the bulk formula. 
      
    In this report, we will describe only the results with
      adjustment scheme.  It has been confirmed that the obtained
      tendency of the deformation of precipitation pattern is
      independent of the choice of cloud parameterization.

\vspace*{0.5em}
%$B?^(B1    SST $BJ,I[(B
\begin{figure}[hbtp]
     \begin{center}
       \Depsf[75mm]{sxrept9ps/SST-a4.ps}
     \end{center}
     \caption{\small The distribution of SST used in experiment A4. 
              The local warm SST area is shaded.
              The figure in the right hand side shows the basic
                SST distribution (solid line) and 
                the distribution at the longitude 180$^{\circ}$, 
                where the value of SST anomaly is the maximum
                (dashed line).}
          \Dfiglab{sst}
\end{figure}
\vspace*{0.5em}

\vspace*{1em}
\noindent
{\bf Experimental Design} 
\vspace*{0.5em}

The surface is all covered by the ocean (aqua-planet)
and the value of SST is fixed. 
The basic SST distribution is the same as
       that used by Numaguti (1993).
     It is symmetric about the equator and zonally uniform. 
     The value of SST at the equator is 302K and remains constant 
       in the equatorial region between the latitudes of $\pm$ 7$^{\circ}$. 
     The shape of the local warm SST area is rectangular 
       with the longitudinal extent of 40$^{\circ}$ and 
       the latitudinal extent of 20$^{\circ}$. 
     The peak value of SST anomaly is 2, 4, 6 or 8K,
       and is located at the center of the warm SST area
       which is placed at the equator. 
     Accordingly, the experiment without SST anomaly is 
        referred to as A0 and
        the experiments with SST anomaly are referred to 
        as A2, A4, A6, and A8 respectively. 
     \Dfigref{sst} shows the SST distributions of A0 and A4.

     For the experiment A0, 
       the model is integrated from
       an isothermal rest state and 
       the data from day 700 to 2200 are used for analyses. 
     For the warm SST area experiments (A2 - A4), 
       the model is integrated from the data at day 700 of A0
       respectively, 
       and the data from day 150 to 900 are used for analyses.
     The model atmosphere is recognized to reach a quasi-equilibrium
       state after 150 days of integration.

%
%---------------------------------------------------------------------
%

\vspace*{1em}
\noindent
{\bf Results: Precipitation Patterns}
\vspace*{0.5em}

      \Dfigref{$B9_?eJ?LL?^(BA4, A4-A0} is 
        the time mean horizontal distribution 
        of the precipitation difference 
        for experiment A4 from the zonal mean distribution of 
        experiment A0. 

        \vspace*{0.5em}
      %$B?^(B2a   A4    $B9_?eJ,I[(B     $B0^EY7PEYJ?LL?^(B (+30$B!A(B-30)
      %   b   A4-A0 $B9_?eJ,I[(B     $B0^EY7PEYJ?LL?^(B (+30$B!A(B-30)
      \begin{figure}[hbtp]
        \begin{center}
          \Depsf[75mm]{sxrept9ps/RAIN-a4sub-tro.ps}
        \end{center}
        \caption{\small Time mean horizontal distribution 
                      of precipitation difference 
                      for experiment A4
                      from the zonal mean distribution 
                      of experiment A0. 
                      Unit is \watt.
                      Contour interval is 20\watt.
                 }
        \Dfiglab{$B9_?eJ?LL?^(BA4, A4-A0}
      \end{figure}
      \vspace*{0.5em}

        The notable feature in \Dfigref{$B9_?eJ?LL?^(BA4, A4-A0} 
          is the deformation of ITCZ.
        There appears an east-west asymmetry in 
          the precipitation distribution at the equator. 
        To the west of the warm SST area,
          the amount of precipitation decreases in the region 
          with the longitudinal extent of about 70$^{\circ}$. 
        To the east of the warm SST area, on the other hand, 
          it increases in the region 
          with the longitudinal extent of about 220$^{\circ}$. 
        The precipitation anomaly has 
          its minimum of $- 100$ \watt  in the western region 
          at the longitude of 150$^{\circ}$
          and its maximum of $+ 60$ \watt  in the eastern region 
          at the longitudes of $220^{\circ}$ and $280^{\circ}$. 
        In the regions along $\pm 10^{\circ}$ latitudes, 
          the amount of precipitation decreases 
          regardless of the eastern or western sides. 
        Precipitation increases only at the longitudes where the warm 
          SST is placed. 

        As for experiments A2, A6 and A8 
          we show only the longitudinal distributions of 
          precipitation at the equator (\Dfigref{$B9_?eJ,I[(B A*-A0}).
        The east-west asymmetry in the precipitation pattern observed in
          experiment A4 is also seen in these experiments;
        the amount of precipitation decreases in the western region
          while it increases in the broad eastern region.
        As the warm SST anomaly increases, 
          the amount of precipitation at the convection center
          increases. 
        However, 
          the increase of precipitation in the eastern region 
          seems to be independent of the magnitude of the SST anomaly. 
        Even a small SST anomaly of experiment A2 
          causes a precipitation increase 
          of the same magnitude as that of experiment A4. 
        On the other hand, 
          the drying in the western region is intensified
          as the warm SST anomaly increases. 
        The western region of experiment A2 is not so dry 
          as that of experiment A4. 
        The drying in experiments A6 and A8 
          is intensified compared to that of experiment A4. 
        Note that in experiments A6 and A8
          the decrease of precipitation occur 
          even in the eastern vicinity of the warm SST area. 

      \vspace*{0.5em}
       %  $B?^(B3
       %  \Dfiglab{$B9_?eJ,I[(B A*-A0}
        \begin{figure}[hbtp]
      \begin{center}
        \Depsf[75mm]{sxrept9ps/RAIN-ADJsub-eq.ps}
      \end{center}
      \caption{\small Longitudinal distributions 
                  of precipitation at the equator 
                  in the warm SST area experiments. 
                Thin solid line, thick solid line, thin dashed line
                  and thick dashed line
                  indicate experiments 
                  A2, A4, A6 and A8, respectively. 
                The zonal mean precipitation value of experiment A0 
                  is subtracted. 
                Unit is \watt.}
      \Dfiglab{$B9_?eJ,I[(B A*-A0}
    \end{figure}
          \vspace*{0.5em}
%
%---------------------------------------------------------------------
%

\vspace*{1em}
\noindent
{\bf The East-West Asymmetry}
\vspace*{0.5em}

      A necessary condition for occurrence of moist convection is that
        the value of $\theta_{e}$ in the lower
        level atmosphere
        is higher than the minimum of $\theta_{e}^{*}$
        (usually located in the middle troposphere).
      According to the numerical results, 
        $\theta_{e}^{*}$ of the warm SST experimnts increases in 
        the middle troposphere ($\sigma \sim 0.55$) 
        both to the east and to the west of the warm SST area,
        and the amount of increase is the larger in the eastern region.
      Since the increase of $\theta_{e}^{*}$ 
        reflects the warming in the middle troposphere,
        its overall increase is qualitatively consistent 
        with the intuitive view 
        in which the atmosphere around a convection center is
        stabilized by the middle tropospheric warming. 
       However, the fact that the eastern region is more stable
        (warmer) than the western region implies that precipitation
        should be more strongly suppressed to the east than to the west.
       The important result is that 
         a significant east-west asymmetry can be observed 
         in the change of $\theta_{e}$ in the lower levels. 
       This zonally asymmetric response is 
         consistent with that of precipitation. 
 
      The increase of low level $\theta_{e}$
        to the east of the warm SST area 
        consists mainly of the increase of humidity; 
        the increase of $\theta_{e}$ 
        due to the temperature change is about 0.2K while 
        that due to the moisture change is about 1K. 
     The increase of the low level humidity to the east of the warm
        SST area should be accounted for either by the increase of 
        evaporation from the ocean 
        or by that of horizontal moisture convergence.

      \vspace*{0.5em}
        %$B?^(B4a   A4-A0 $B>xH/(B $B0^EY7PEYJ?LL?^(B  (+30$B!A(B-30)
        %   b   A4-A0 $P-E$ $B0^EY7PEYJ?LL?^(B  (+30$B!A(B-30)
        \begin{figure}[hbtp]
      \qquad{\bf (a)}
      \begin{center}
        \Depsf[75mm]{sxrept9ps/EVAP-a4sub-tro.ps}
      \end{center}
      \qquad{\bf (b)}
      \begin{center}
        \Depsf[75mm]{sxrept9ps/P-E-a4sub-tro.ps}
      \end{center}
      \caption{\small Horizontal distributions of 
                (a) evaporation and (b) $P-E$  of experiment A4. 
                Unit is \watt. The zonal mean values of
                experiment A0 are subtracted, respectively.
               }
      \Dfiglab{$B>xH/(B, $P-E$ $BJ?LL?^(BA4-A0}
        \end{figure}
      \vspace*{0.5em}

     Now, we will evaluate the relative importance of 
        the two candidates, WISHE and CISK,
        by examining the response of evaporation
        and that of the difference between precipitation and evaporation
        (indicated by $P-E$ below) which reflects the horizontal
        moisture convergence. 
     \Dfigref{$B>xH/(B, $P-E$ $BJ?LL?^(BA4-A0}(a) shows 
        the difference in evaporation (E) in the tropics 
        between experiments A4 and A0,
        and \Dfigref{$B>xH/(B, $P-E$ $BJ?LL?^(BA4-A0}(b) is that
        for $P-E$.
     Around $\pm 7^{\circ}$ latitudes to the east of the warm SST area, 
        a slight increase of evaporation is found. 
     However, against the previous expectation on WISHE, 
        the equatorial response to the east of the warm SST area is
        negative. 
     On the other hand, $P-E$ increases
        at the equator to the east of the warm SST area. 
     As $P-E$ equals a horizontal moisture convergence in the 
        equilibrium state, 
        this indicate the existence of significant horizontal
        moisture convergence at the equator to the east of the warm
        SST area.  
     It is evident that the change of evaporation 
        does not play an important role in moistening at
        the equator.
      
      \vspace*{0.5em}
%  $B?^(B5
%  \Dfiglab{$B9_?e>xH/7PEYJ,I[(BA4-A0}
%   a   A4-A0 $B9_?e(B, $B>xH/(B $B@VF;>e$N7PEYJ,I[(B
%   b   A4-A0 $B9_?e(B, $B>xH/(B -30$B!A(B+30 $BJ?6Q$N7PEYJ,I[(B
\begin{figure}[hbtp]
      \qquad{\bf (a)}
      \begin{center}
        \Depsf[75mm]{sxrept9ps/RAINEVAP-a4sub-eq.ps}
      \end{center}
      \qquad{\bf (b)}
      \begin{center}
        \Depsf[75mm]{sxrept9ps/RAINEVAP-a4sub-ym30.ps}
      \end{center}
      \caption{\small Longitudinal distributions of precipitation
                 (solid line) 
                  and evaporation (dashed line)
                  of experiment A4 (a) at the equator 
                  and (b) averaged in the meridional area 
                  between $\pm 30$$^{\circ}$ latitudes. 
                Unit is \watt. 
                The zonal mean values of experiment A0 
                  are subtracted, respectively.
               }
      \Dfiglab{$B9_?e>xH/7PEYJ,I[(BA4-A0}
\end{figure}
      \vspace*{0.5em}

    In order to show the responses more clearly, 
        the changes of evaporation and precipitation at the 
        equator are plotted in \Dfigref{$B9_?e>xH/7PEYJ,I[(BA4-A0}(a).
     Again, it is evident that precipitation is enhanced to the east of 
        the warm SST area and suppressed to the west.
     The change in evaporation, on the other hand, is very small
        compared to that of precipitation
        except for over the warm SST area.


    \Dfigref{$B9_?e>xH/7PEYJ,I[(BA4-A0}(b) shows the longitudinal 
        distributions of the changes of precipitation and evaporation
        averaged meridionally between $\pm 30^{\circ}$ latitudes.
     There is no east-west asymmetry in the 
        evaporation response, just as at the equator. 
     WISHE does not operate even as the 
        meridional average over the whole tropical latitudes.

    By comparing \Dfigref{$B9_?e>xH/7PEYJ,I[(BA4-A0}(a) 
        and \Dfigref{$B9_?e>xH/7PEYJ,I[(BA4-A0}(b), 
        we can recognize that
        the increase of precipitation in the eastern region 
        at the equator (\Dfigref{$B9_?e>xH/7PEYJ,I[(BA4-A0}a) 
        is compensated by the 
        decrease of that in the subtropics, 
        resulting in little change in the meridionally averaged 
        precipitation (\Dfigref{$B9_?e>xH/7PEYJ,I[(BA4-A0}b). 
     This suggests 
        that the equatorial precipitation enhancement to the east 
        of the warm SST area is 
        accounted for by the change of meridional moisture transport. 
    The enhancement of precipitation at the equator 
        by the change of the meridional moisture flux 
        to the east of the warm SST area 
        can be recognized also in the other experiments
        with different amplitudes of the warm SST anomaly.

     In order to evaluate the effect of WISHE more completely, 
        experiment A4VC is conducted in which WISHE is 
        excluded artificially. 
     In experiment A4VC, 
       the surface wind speed used in this evaporation bulk formula is 
       held constant in time in 
       the tropical region between the latitudes of $\pm$ 30$^{\circ}$.
     The fixed value of constant wind speed is obtained from
       the temporal and zonal mean of experiment A0 
       except for the warm SST area where the temporal mean value
       of experiment A4 is used.
     The initial condition of experiment A4VC 
        is the data at day 2200
        of experiment A0 
        and is integrated for 900 days and the data of the last 500
        days is used for the following analyses (not shown here).
     The result showed that the
       precipitation at the equator
       to the east of the warm SST area increases significantly
       from that of experiment A0. 
     The response in $P-E$ 
       is quite similar to 
       that of experiment A4, 
     which means that the precipitation response is strongly connected
        to the horizontal moisture convergence. 
     WISHE plays at most secondary
        role in the generation of the zonally asymmetric response of
        precipitation. 


%
%---------------------------------------------------------------------
%

\vspace*{1em}
\noindent
{\bf Concluding Remarks}
\vspace*{0.5em}

  By a series of aqua planet experiments
     with a localized warm SST area with various intensities,
     following conclusions are obtained.
  The response to a warm SST area placed at the equator is that
     precipitation is enhanced in an extensive region 
     to the east of the warm SST area
     while drying occurs to the west.
   The increase of precipitation in the eastern region 
     results from the increase of meridional moisture convergence
     associated with the frictional inflow converging
     into the low pressure area 
     existing to the east of the warm SST area.
   The decrease of precipitation in the western region is associated 
     with downward flow and an increase of stability due to a 
     temperature rise in the middle layer. 
   WISHE does not play an important role in the generation 
     of the east-west asymmetry of the precipitation response. 

  By comparing the results of the two series of experiments with 
     the different cumulus parameterization schemes 
     (the adjustment scheme and the Kuo scheme),
     the structure of the precipitation response is found to be
     insensitive to the choice of cumulus parameterization scheme.
   The east-west asymmetric response of precipitation obtained in the
     present study is robust in this sense.  

   The characteristic that an intense dry region appears 
        to the west of an active convection center 
        is found in the real tropical atmosphere and the GCM
        experiments. 
    During the ENSO warm events, 
        strong droughts are observed to the west of the 
        warm SST anomaly areas in the equatorial Pacific 
        (Ropelewski and Halpert 1987). 
    In the 82--83 ENSO warm event, 
        the decrease of cumulus activity is clearly shown by the
        OLR observation (e.g., Arkin {\it et al.} 1983); 
        it is reported that forest fires occurred even in the
        tropical rain forest of Borneo
        (Tsuyuki, 1988)
        \footnotemark. 
        \footnotetext{The forest fires of 97 event are recently
                reported to be even more severe.}
    In the GCM SST anomaly experiments, 
        dry areas also appear to the west of the anomalous regions 
        (e.g., 
        Keshavamurty, 1982; 
        Geisler {\it et al.}, 1985; 
        Wu and Liu, 1992). 
    As for the climatic precipitation distribution, 
        there appear small rainfall regions to the west of 
        the convection centers 
        (Spencer, 1993). 
    For instance, 
        the heavy convection activity over the Maritime Continent 
        does not extend westward far into the Indian Ocean  
        along the equator. 
    The reason for the small rainfall is usually considered as a 
        result of low SST values in the corresponding region.
    However, 
        even if the values of SST to the eastern and western sides are the 
        same, 
        the results of present research show that 
        a dry region extends to the west of the convection center. 
    The characteristics exemplified in our numerical calculations
        contribute at least partly to the formation of precipitation
        patterns to the west of the real convection centers. 

%
%---------------------------------------------------------------------
%

\vspace*{1em}
\noindent
{\bf Acknowledgment}
\vspace*{0.5em}

We wish to thank all of the staff members of CGER
for providing us with this powerful computing facility. 
Our software environment was provided from the resources of GFD 
Dennou Club (http://www.gfd-dennou.org/). 

%
%---------------------------------------------------------------------
%
\vspace*{1em}
\noindent
{\bf References}
\vspace*{0.5em}
\begin{description}
\small
  \item Arkin, P.A., Kopman, J.D.  and Reynolds, R.W.  (1983)
    1982-1983 El Nino / Southern Oscillation event quick look atlas.
    NOAA / National Weather Service, National Meteorological Center,
    Climate Analysis Center, Washington D. C. 20323. 
        \vspace*{-1em}
  \item Geisler, J. E., Blackmon, M. L., Bates G. T. and Munoz, S. (1985) 
        Sensitivity of January climate response to the magnitude 
        and position of equatorial Pacific sea surface temperature anomalies.
        {\it J. Atmos. Sci.}, {\bf 42}, 1037-1049. 
        \vspace*{-1em}
  \item Golitsyn, G.S. (1970) 
        A similarity approach to the general circulation of planetary 
        atmospheres. \\
        {\it ICARUS}, {\bf 13}, 1-24.
        \vspace*{-1em}
  \item Hayashi, Y.-Y.  and Sumi, A. (1986) 
        The 30-40 day oscillations simulated in an ``aqua planet'' model.
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\end{description}




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