Global Well-Posedness of the Fractional Tropical Climate Model ()
1. Introduction
In this paper, we consider the following tropical climate model with fractional diffusion and nonlinear damping terms
(1.1)
(1.2)
(1.3)
(1.4)
(1.5)
where
, the vector fields
and
denote the barotropic mode and the first baroclinic mode of the velocity, respectively. The scalar functions
and
represent the pressure and the temperature, respectively.
,
,
,
,
,
,
,
,
,
,
,
are real parameters. For
, the fractional Laplacian operator
is defined through the Fourier transform
The tropical climate model (1.1) - (1.5) was originally introduced by Frierson-Majda-Pauluis in [1] without any dissipation terms (
) in order to perform a Galerkin truncation to the hydrostatic Boussinesq equations. For more background about the tropical climate model, we refer to [2] . If the effect of temperature is ignored, the system is similar in form to the generalized MHD equation with divergence free condition both on u and v.
Firstly, we recall some global existence results for the tropical climate model without any damping terms. Ye [3] obtained global regularity for a class of 2-dimensional tropical climate model with
,
. Li and Titi [4] established the 2-dimensional global well-posedness of strong solution for the system with
,
by introducing a combined quantity called pseudo baroclinic velocity. Wan [5] proved the global well-posedness of the classical solutions to the climate model with the dissipation of the first baroclinic model of the velocity and some damping terms (
,
,
,
). Dong et al. [6] investigated the case when
,
,
or
,
and obtained global regularity of 2-dimensional tropical climate models in
. Zhu [7] established the regularity for the tropical climate model with
,
,
and
in
. In [8] the authors analyzed the d-dimensional (
) tropical climate model with only
. By choosing a class of special initial data
whose
norm can be arbitrarily large and obtained the global smooth solution of d-dimensional tropical climate model. Yu, Li and Yin establish the global regularity for the system with
,
,
and
in [9] . Niu and Wang [10] dealt with the global well-posedness and large-time behavior of the 2D tropical climate model with small initial data for
,
and
,
,
.
Next, we will give some global existence results for the system. The global existence and uniqueness of a strong solution is established provided
with
,
,
by Yuan and Chen [11] . Yuan and Zhang [12] proved the global regularity assuming that one of the following three condition holds true: 1)
, 2)
,
,
, 3)
,
with
. Berti, Bisconti and Catania in [13] provided a regularity criterion to obtain the smoothness of the solutions with
,
,
, and
,
.
Since the specific values of
do not play a special role in our discussions, for the sake of simplicity, we set
in the rest of the paper.
We have proved the local existence of the fractional tropical climate model for
in
,
. When
, for our global existence in this paper, because of the shortcoming of the damping terms, we can verify that
to ensure
. The local existence for this paper can be established by the procedure of the local existence of the fractional tropical climate model for
in
,
and Lemma 2.3, thus it is omitted here.
It should be noted that all the above mentioned works for the system require the restriction that at least one of the
must greater than or equal to 1. A natural question is that what would happen if they were all less than 1. In this paper, the focus of our work is to discuss the global exitence when all
are less than
. Also, we improved the previous global solution when
greater than
, which is meaningful.
Our main results are stated as follows:
Theorem 1.1. Assume
with
If
then, for any
, the system (1.1) - (1.5) has a global strong solution
such that
Theorem 1.2. Assume
with
If
then, for any
, the system (1.1) - (1.5) has a global strong solution
such that
Theorem 1.3. Assume
and
with
. If
then, for any
, the system (1.1) - (1.5) has a global strong solution
such that
Throughout the whole paper, we use
to denote the
norm.
and
denote the homogeneous Sobolev space with the norm
and nonhomogeneous Sobolev space with the norm
, respectively. C denotes a generic positive constant, and it may be different from line to line.
We find that when
are relatively large, with the help of dissipative terms, the global existence is relatively easy to obtain. But when all
are relatively small, the global existence is not easy to obtain, and it needs to be controlled by damping terms.
2. Preliminaries
We state the Gagliardo-Nirenberg inequality in Lemma 2.1 and the Kato-Ponce type inequality in Lemma 2.2.
Lemma 2.1. ( [14] ) Let u belongs to
in
and its derivatives of order m,
, belong to
,
. For the derivative
,
, the following inequality holds
(2.1)
where
(2.2)
for all
in the interval
(2.3)
Lemma 2.2 ( [15] ) Let
,
, then we have
(2.4)
with
.
Lemma 2.3 ( [16] ) For
,
and
, we have
where
3. Proof of the Theorem 1.1
Proof. Multiplying (1.1), (1.2), (1.3) respectively by
, after integrating by parts and taking the divergence free property into account, we have
(3.5)
Next, applying the operator
to (1.1), (1.2), (1.3) and taking the
inner product to the resultants with
, after integrating by parts, we have
(3.6)
Integration by parts implies
(3.7)
Because of the divergence-free condition of u, the estimates for
,
,
and
are similar, and we take the detailed estimate for
as an example.
For
, when
, using Kato-Ponce type inequality and Young’s inequality, we can get
here we have used the following Gagliardo-Nirenberg inequality
(3.8)
Note that
implies
and
. Letting
, which means
.
Therefore, we need
and
. Then, we get
(3.9)
Similarly, for the terms
,
and
, we can obtain the following estimates
(3.10)
(3.11)
and
(3.12)
It remains to estimate the term
. However, this term can not be treated as above due to the non-divergence free property of v, so we estimate
as follows
For
, similarly to 3.9, we obtain
and for
, we have
where
with
and
which implies that
.
Therefore, we have
(3.13)
Taking the above estimations (3.9) - (3.13) into (3.6), we obtain that
(3.14)
This completes the proof of the Theorem 1.1 by Gronwall’s inequality and energy estimate (3.5).
4. Proof of the Theorem 1.2
Proof. Multiplying (1.1), (1.2), (1.3) respectively by
, after integrating by parts and taking the divergence free property into account, we have
(4.15)
Next, applying the operator
to (1.1), (1.2), (1.3) and taking the
inner product to the resultants with
, after integrating by parts, we have
(4.16)
Integration by parts implies
(4.17)
We take the detailed estimate for
as an example.
For
, when
, using Kato-Ponce type inequality, we can get
with
,
. Here, we can yeild
.
Then, we have
(4.18)
Due to the non-divergence free condition we have used, so we can obtain other terms using the same way. Then we have
(4.19)
(4.20)
(4.21)
and
(4.22)
Taking the above estimations (4.17) - (4.22) into (4.16), we obtain that
This completes the proof of the Theorem 1.2 by Gronwall’s inequality and energy estimate (4.15).
5. Proof of the Theorem 1.3
Proof. Multiplying (1.1), (1.2), (1.3) respectively by
, after integrating by parts and taking the divergence free property into account, we have
(5.23)
For the
-estimates:
Next, applying the operator
to (1.1), (1.2), (1.3) and taking the
inner product to the resultants with
, after integrating by parts, we have
(5.24)
Integration by parts implies
(5.25)
We also consider
first.
(5.26)
here, we need
and have used the following inequalities
Similarly, we can obtain
as follows
(5.27)
Though above estimate for
and
, we know that we don’t need to use the divergence free condition. Therefore, we can obtain
(5.28)
(5.29)
(5.30)
Taking the above estimations (5.25) - (5.38) into (5.24), we obtain that
(5.31)
For the
-estimates:
Taking
to (1.1), (1.2), (1.3), multiplying (1.1), (1.2), (1.3) by
,
,
, after integrating by parts and taking the divergence free property into account, we have
(5.32)
Integration by parts implies
(5.33)
We consider
first.
(5.34)
here, we have used the following inequalities
By the Kato-Ponce, Hölder, Gagliardo-Nirenberg and Young inequalities, we have
(5.35)
(5.36)
(5.37)
(5.38)
Taking the above estimations (5.25) - (5.38) into (5.24), we obtain that
(5.39)
For the
-estimates:
Taking
to (1.1), (1.2), (1.3), multiplying (1.1), (1.2), (1.3) by
,
,
, after integrating by parts and taking the divergence free property into account, we have
(5.40)
Integration by parts implies
(5.41)
Now, we estimate the terms in the right side of (5.40) one by one
(5.42)
(5.43)
Similarity,
(5.44)
The most difficulty are the following two terms.
For
, we can estimate it as follows
For
, we have
Similarity,
Therefore, we can get
This completes the proof of the Theorem 1.3 by Gronwall’s inequality and energy estimate (5.23).