Faculty Profiles - MASUNAGA, Hirohiko

Papers - MASUNAGA, Hirohiko

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Physical Properties of Maritime Low Clouds as Retrieved by Combined Use of TRMM Microwave Imager and Visible/Infrared Scanner. Algorithm. Reviewed

Masunaga, H., T. Y. Nakajima, T. Nakajima, M. Kachi, R. Oki, and S. Kuroda

J. Geophys. Res. Vol. 107 ( D10 ) page： doi:10.1029/2001JD000743 2002

Authorship：Lead author Language：English Publishing type：Research paper (scientific journal)

Satellite remote sensing studies on the microphysical and optical properties of clouds have
constructed an active research field in the last decades. Clouds are observed over a wide spectral
range from the visible/infrared to the microwave, and either shortwave or microwave measurement
is used to evaluate the liquid water path (LWP). On the other hand, to date, there have been few
cloud studies based on combined measurement by a visible/infrared imager and a microwave
radiometer aboard the same platform. In this paper a physical inversion algorithm for the combined
use of visible/infrared and microwave sensors is proposed to retrieve the cloud physical quantities
such as LWP and the effective droplet radius, each of which is determined in two different ways.
The current version of the algorithm has been developed for application to the Tropical Rainfall
Measurement Mission (TRMM) sensors, i.e., Visible and Infrared Scanner (VIRS) and TRMM
Microwave Imager (TMI). The cloud top temperature obtained from the VIRS analysis is used as an
input to the TMI analysis to reduce uncertainties in estimation of LWP. Total errors in LWP are
estimated to range from 11 to 30 g /m2. In the algorithm the beam-filling efficiency of clouds for
TMI footprints is corrected by the cloud fraction evaluated from the VIRS measurements. For
application, global analysis is performed with 3-monthly data from January to March 2000. The
scatter diagram of the shortwave-retrieved LWP (LWPshrt) versus the microwave-retrieved LWP
(LWPmicr) shows characteristic trends for both precipitating and nonprecipitating clouds. Vertical
inhomogeneity of the cloud droplet size accounts for small excess of LWPshrt over LWPmicr for
nonprecipitating clouds, while precipitating clouds produce LWPmicr larger than LWPshrt, owing to
the presence of raindrops. These tendencies are reinforced by examination of the global
distributions of the shortwave-retrieved droplet radius Re (NV) and the microwa

Comparison of Rainfall Products Derived from TRMM Microwave Imager and Precipitation Radar. Reviewed

Masunaga, H., T. Iguchi, R. Oki, and M. Kachi

J. Applied Meteor. Vol. 41 page： 849-862 2002

Authorship：Lead author Language：English Publishing type：Research paper (scientific journal)

Satellite remote sensing is an indispensable means of measuring and monitoring precipitation on a global scale.
The Tropical Rainfall Measuring Mission (TRMM) is continuing to make significant progress in helping the global
features of precipitation to be understood, particularly with the help of a pair of spaceborne microwave sensors,
the TRMM Microwave Imager (TMI) and precipitation radar (PR). The TRMM version-5 standard products,
however, are known to have a systematic inconsistency in mean monthly rainfall. To clarify the origin of this
inconsistency, the authors investigate the zonal mean precipitation and the regional trends in the hydrometeor
profiles in terms of the precipitation water content (PWC) and the precipitation water path (PWP) derived from
the TMI profiling algorithm (2A12) and the PR profile (2A25). An excess of PR over TMI in near-surface PWC
is identified in the midlatitudes (especially in winter), whereas PWP exhibits a striking excess of TMI over PR
around the tropical rainfall maximum. It is shown that these inconsistencies arise from TMI underestimating the
near-surface PWC in midlatitude winter and PR underestimating PWP in the Tropics. This conclusion is supported
by the contoured-frequency-by-altitude diagrams as a function of PWC. Correlations between rain rate and PWC/
PWP indicate that the TMI profiling algorithm tends to provide a larger rain rate than the PR profile under a given
PWC or PWP, which exaggerates the excess by TMI and cancels the excess by PR through the conversion from
precipitation water to rain rate. As a consequence, the disagreement in the rainfall products between TMI and PR
is a combined result of the intrinsic bias originating from the different physical principles between TMI and PR
measurements and the purely algorithmic bias inherent in the conversion from precipitation water to rain rate.

Physical Properties of Maritime Low Clouds as Retrieved by Combined Use of TRMM Microwave Imager and Visible/Infrared Scanner. II. Climatology of Warm Clouds and Rain. Reviewed

Masunaga, H., T. Y. Nakajima, T. Nakajima, M. Kachi, and K. Suzuki

J. Geophys. Res Vol. 107 ( D19 ) page： doi:10.1029/2001JD001269 2002

Authorship：Lead author Language：English Publishing type：Research paper (scientific journal)

In this paper, we investigate characteristics of low clouds and warm-rain production in
terms of droplet growth based on the effective droplet radii retrieved by a combined use of
visible, infrared, and microwave satellite remote sensing. We propose to categorize low
clouds into the following groups: (1) nondrizzling, nonraining clouds; (2) nonraining
clouds with drizzling near the cloud top; (3) raining clouds; and (4) clouds with no clear
interpretation in terms of the effective radii derived using two different schemes. This
categorization is supported by examination of the correlation between static stability and
the retrieved results in the three ``precipitating regions'' (the Middle Pacific, South Pacific
Convergence Zone [SPCZ], and Intertropical Convergence Zone [ITCZ] cumulus regions)
and in the four ``nonprecipitating regions'' (the Californian, Peruvian, Namibian, and
eastern Asian stratus regions). The rain rate derived by Precipitation Radar (PR) provides
global characteristics consistent with our results. Californian and Peruvian stratus clouds
are found to frequently have the drizzle mode near the cloud top, whereas Namibian strati
have fewer chances to drizzle. The drizzle mode almost completely disappears in the
eastern Asian region in the winter. The cloud–aerosol interaction is a promising candidate
for suppressing the drizzle mode formation in nonprecipitating clouds.

The Effective Cloud Fraction of Broken Clouds Obtained by Multi-stream Radiative Transfer. I. Longwave Radiation Reviewed

Masunaga, H. and T. Nakajima

J. Atmos. Sci. Vol. 58 page： 2455-2467 2001

Authorship：Lead author Language：English Publishing type：Research paper (scientific journal)

The influence of broken clouds on radiative flux has provided a major source of uncertainty in radiative
transfer models of the atmosphere because plane-parallel approximations are assumed in most of the current
atmospheric models, where horizontal inhomogeneity cannot be adequately taken into account. In this paper,
effects by cloud inhomogeneity on longwave radiation fields are investigated, using a simple model of a cloud
array that consists of identical cuboids following some past studies. In contrast to past work that adopted simplified
formulations of radiative transfer, multistream radiative transfer is considered to obtain the exact solutions of
radiative flux, which enable us to consider semitransparent clouds as well as optically thick clouds in desirable
accuracy. Applicability to semitransparent clouds is important because cirrus clouds, which are considered to
play significant roles for longwave radiation, are often semitransparent to infrared radiation.
The computational results show that the empirical formula previously derived by Harshvardhan and Weinman
systematically underestimates the effective cloud fraction. An alternative formula is proposed for the effective
cloud fraction to supply a better fit to the exact solution of radiative flux. Furthermore, new formulas are derived
to approximate the exact solutions including the dependence on the optical thickness of clouds. They are useful
to convert plane-parallel flux to 3D flux passing through broken clouds, either for optically thick or thin clouds.

A Radiation Hydrodynamic Model for Protostellar Collapse II. The Second Collapse and The Birth of a Protostar. Reviewed

Masunaga, H. and Inutsuka, S.

Astrophys. J. Vol. 531 page： 350-365 2000

Authorship：Lead author Language：English Publishing type：Research paper (scientific journal)

carry out radiation hydrodynamic calculations to study physical processes in the formation of a 1
M protostar. Following our previous work, calculations pursue the whole evolution from the beginning _
of the Ðrst collapse to the end of the main accretion phase. The adiabatic core formed after the initial
collapse (i.e., the Ðrst core) experiences further gravitational collapse triggered by dissociation of molecular
hydrogen, which leads to the formation of the second core, i.e., the birth of a protostar. The protostar
grows in mass as accreting the infalling material from the circumstellar envelope, while the protostar
keeps its radius at D4 R during the main accretion phase. These typical features in the evolution are in _
good agreement with previous studies. We consider two dierent initial conditions for the density distribution
: homogeneous and hydrostatic cloud cores with the same central density of 1.415]10~19 g
cm~3 . The homogeneous core has the total mass of 1 M while the hydrostatic core has 3.852 For _ M_.
the initially homogeneous model, the accretion luminosity rapidly rises to the maximum value of 25 L _
just after the birth of a protostar, and declines gradually as the mass accretion rate decreases. In contrast,
the luminosity increases monotonically with time for the initially hydrostatic model. This dierence
arises because the mass accretion rate varies depending on the inward acceleration at the initial stage,
which aects the luminosity curve. A less massive hydrostatic core would possess the similar properties
in the luminosity curve to the 3.852 M case, because a hydrostatic cloud core with mass lower than _
3.852 M can be shown to provide a smaller mass accretion rate after the birth of a protostar and a _
more gradual rise in the luminosity curve. Our numerical code is designed to provide the evolution of
the spectral energy distribution (SED) along with the dynamical evolution in our spherically sym

Infall Signatures in Molecular Line Spectra of Protostellar Envelopes. Reviewed

Masunaga, H. and Inutsuka, S.

Astrophys. J. Vol. 536 page： 406-415 2000

Authorship：Lead author Language：English Publishing type：Research paper (scientific journal)

A double-peaked proÐle with a stronger blue peak in a molecular line spectrum is considered strong
evidence for the infall motion in the gas envelope surrounding a protostar. Some past studies performed
model calculations for reproducing observed spectral proÐles using simpliÐed dynamical models such as
isothermal similarity solutions. However, validity of the similarity solutions for spectral line synthesis
should be examined in comparison with more realistic dynamical models.
In this paper we carry out theoretical modeling of molecular line spectra, adopting a spherically symmetric
radiation hydrodynamical model for protostar formation taken from a recent work by the
authors. This study concentrates on how infall motions could account for the asymmetric line proÐles
observed toward protostellar sources. We do not explicitly consider the eects of rotation and outÑows
on the generation of line proÐles. In our numerical code for the non-LTE line transfer, the level populations
are fully consistent with the radiation Ðeld under an arbitrary physical structure in spherical symmetry,
and hence, reliable spectral synthesis has been enabled and compared to the LTE, large velocity
gradient (or Sobolev), and microturbulence approximations.
Contrary to the remarks by Zhou, we do not Ðnd an overestimation of line widths, although the
dynamical evolution resembles the Larson-Penston solution rather than the expansion-wave solution.
Furthermore, the infall motion produces wings extending to v\^2 km s~1 in line spectra, in contrast
to previous works where wings could not be produced by infall models. These results imply that simpli-
Ðed infall models, such as the isothermal similarity solutions adopted by previous authors, are not
always suitable to the detailed modeling of line spectra.

Does "t @ 1" Terminate the Isothermal Evolution of Collapsing Clouds? Reviewed

Masunaga, H. and Inutsuka, S.

Astrophys. J. Vol. 510 page： 822-827 1999

Authorship：Lead author Language：English Publishing type：Research paper (scientific journal)

We examine when gravitationally collapsing clouds terminate their isothermal evolution. According to
our previous work, the condition with which isothermality is broken down is classiÐed into three cases,
i.e., when (1) the compressional heating rate overtakes the thermal cooling rate, (2) the optical depth for
thermal radiation reaches unity, or (3) the compressional heating rate becomes comparable with the
energy transport rate because of radiative diusion. In the present paper this classiÐcation is extended to
dmiseoontrhseietirgemesnawelrieatvhl ovwluahltuiiocehns otchef eatssheeesciwonnhitdeiiantlioccnalsoseuad1retoesrma3tpiseiÐsreasdtau.triFesÐoTeridnp,itlaaanundsdibcloaepseavca2iltuyheasis,onfaonTdisniigtwnaeinÐddceatine,cremw. eiWneÐentdehmethpcahrtiatsitcihzaeel
that the condition of qB1 ÏÏ never terminates isothermality, but nonisothermal evolutions begin either
earlier or later depending on the initial temperature and opacity. This result contrasts with the conventional
idea that opaqueness breaks isothermality. On the basis of the critical density discussed above, the
minimum Jeans mass for fragmentation, MF, is reconsidered. In contrast to the results by previous
authors that MF is insensitive to Tinit and i, we Ðnd that MF can be substantially larger than the typical
value of D10~2 M depending on and i. In particular, increases with decreasing metallicity, _ Tinit MF
MFPi~1, for low-metal clouds. A cloud with i\10~4 cm2 g~1 and Tinit\10 K yields MF\3.7 M_.
Finally, our critical densities would be helpful for hydrodynamic simulations that are intended to simply
handle the hardening of the equation of state.

A Radiation Hydrodynamic Model for Protostellar Collapse I. The First Collapse. Reviewed

Masunaga, H., Miyama, S.M., and Inutsuka, S.

Astrophys. J. Vol. 495 page： 346-369 1998

Authorship：Lead author Language：English Publishing type：Research paper (scientific journal)

Dynamical collapse of a molecular cloud core and the formation of a star are investigated by performing
radiation hydrodynamic calculations in spherical symmetry. The angle-dependent and
frequency-dependent radiative transfer equation is solved without any di†usion approximations, and the
evolution of the spectral energy distribution (SED) is examined.
In the present paper, as the Ðrst step in a series of our work, evolutions before hydrogen molecules
begin to dissociate (the so-called Ðrst collapse) are examined for di†erent masses and initial temperatures
of the parent cloud cores and for di†erent opacities. Numerical results for a typical case [Tinit\10 K
and iP(10 K)D0.01 cm2 g~1] show that the radius and mass of the Ðrst core are D5 AU and D0.05
M respectively. These values are independent both of the mass of the parent cloud core and of the _,
initial density proÐle. The analytical expressions for the radius, mass, and accretion luminosity of the
Ðrst core are also obtained. The SED contains only cold components of a few times 10 K throughout
the Ðrst collapse phase, because the opaque envelope veils the Ðrst core from observers. We suggest that
the molecular cloud cores with luminosities higher than D0.1 L should contain young protostars deep _
in the center, even if they show no evidence for the existence of central stars in near-infrared and optical
observations.

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