Historically the Heisenberg lower limit is used as the reference level
for the definition of squeezing in observables. However, in the measu
rement of observables corresponding to noncanonical operators, it may
not work [Puri, Phys. Rev. A49, 2178 (1994)]. Then, one should employ
the Schrodinger uncertainty relation for further studies, where the Sc
hrodinger lower limit sets a higher bound on quantum fluctuations than
the Heisenberg one does. In this paper, using Heisenberg's and Schrod
inger's uncertainty relations, we have made a comparative study on the
squeezing properties of quantum fluctuations in atomic dipole variabl
es in the thermal two-photon Jaynes-Cummings model, including the disc
ussion of the difference between both cases, the influence of initial
atomic coherence or thermal photons on the atomic dipole squeezing, an
d the possibility of realization of atomic dipole squeezing in two-pho
ton micromaser experiments with Rydberg atoms in a high-Q cavity.