Due to the rotation of the Earth, solar heating is applied to the Earth with different harmonics of the day length. One of the dominant signals is the diurnal one with a 24hr period in the response of the atmosphere. The thesis investigates diurnal atmospheric circulations in two geographical scales: namely kilometers and thousands of kilometers.

Stations from dry western valleys show the largest diurnal surface pressure amplitudes (∼200 Pa) and the earliest phases (0600 LST for surface pressure maximum). The origin of these unique characteristics is examined using a detailed study of Owens Valley, California. Analysis of the intense observations from the Terrain-Induced Rotor Experiment (T-REX) project shows that the ratio of the valley surface pressure to temperature amplitude can be used to estimate the daily maximum mixed-layer depth. On days with strong westerly winds above the valley, the mixed layer is found to be shallower than on quiescent days because of a flushing effect in the upper parts of the valley. An idealized 2d Weather Research and Forecasting (WRF) Model is used to simulate diurnal valley circulation. In agreement with observations, the simulations show a 3-hour difference between the occurrence of a surface pressure minimum (1800 LST) and a surface temperature maximum (1500 LST). The resolved energy budget analysis reveals that this time lag is caused by the persistence of subsidence warming in the upper part of the valley after the surface begins to cool. Sensitivity tests for different valley depths and seasons show that the relative height of the mixed-layer depth with respect to the valley depth, along with the valley width-to-depth ratio, determine whether the diurnal valley circulation is a "confined" system or an "open" system. The open system has smaller pressure amplitude and earlier pressure phase.

Stations from the Great Plains and Midwest show the known eastward moving diurnal summer precipitation anomaly and a large sun-following continentally enhanced tide. Optimization using the "temperature based tide assumption" reveals a smaller pressure signature moving eastward along with the precipitation. This eastward wave has a variable speed and amplitude. This pressure "wave" is also present on dry days, and in winter, indicating that it is the cause of the precipitation anomaly, not the result. A possible mechanism for the pressure wave is developed from the linear Bousinesq equations with heating and wind shear. In addition to the inhomogeneous continental tide, it shows eastward moving diurnal pulses of potential vorticity (PV) generated by imposed heating over the Rockies. Because of the background shear, they produce vertical motion in the lower troposphere. The PV hypothesis is tested with the North American Regional Reanalysis (NARR) data. Diurnal drifting PV anomalies are found around the 500 to 600 hPa level in both winter and summer. In winter the PV anomalies are weaker, seem to form further west, and they do not trigger convection.