Coupling of Clouds and Tropospheric Relative Humidity in the Tropical Western Atlantic: Insights From Multisatellite Observations

Abstract

We investigated the interactions between clouds and moisture at the diurnal scale in the Western Atlantic trade winds region. Profiles of tropospheric relative humidity from the SAPHIR/Megha-Tropiques sounder are combined with cloud categories obtained from geostationary satellites. In winter, the midtroposphere undergoes strong daytime drying due to air masses coming from the colder upper troposphere. The moistening near the surface triggered by solar radiation precludes the development of low-level clouds. At night rising moist air in the upper troposphere triggers the formation of high-altitude clouds and favors their presence. In summer, daytime high-altitude clouds shield the solar forcing on the atmosphere and reduce drying from large-scale subsidence. After sunset, the development of upper tropospheric opaque clouds constitutes a local source of moisture. We argue that modulations of the diurnal cycle of clouds and relative humidity by season may be related to diurnal pulses of the Intertropical Convergence Zone. Plain Language SummaryThe heat engine of the climate is the atmospheric water cycle.Understanding the relationships between clouds and the atmospheric relative humidity is crucial to improve our understanding of climate variability. Here we focus on the diurnal fluctuations of vertical profiles of tropospheric relative humidity and collocated clouds in the tropical Western Atlantic trade winds region. Profiles of water vapor and distribution of clouds, classified by altitudes, are obtained from spaceborne instruments, and the other environmental characteristics such as sea surface and air temperatures are extracted from a weather model. Their joint diurnal variations are examined. Winter and summer seasons are compared. The diurnal water vapor cycle of water vapor evolves from the bottom to the top of the atmosphere and is strongly associated with cloud types, with a seasonal modulation. During daytime a strong drying is associated with the downward dry air masses moving downward. The diurnal cycle of upper-level cloudiness plays a critical role in inhibiting daytime drying by shielding the midtroposphere from this downward transport. The upper-level moisture feeds upper-level clouds and modulates their diurnal lifetime.

ENTICE Satellite Orbital Simulator to Study Ice Clouds

“…Figures 8 and 9 show ENTICE sample size for ice clouds with different ranges of IWP values in the two different regions TWA and TWP respectively. These regions were chosen not only for the large amount of high clouds present (Brogniez & Kirstetter, 2020; Hartmann & Berry, 2017), but also because the TWA has a significant pattern of moderate deep convective core occurrence and the TWP is known for its frequently occurring mesoscale convective systems (Houze et all). Four IWP bins are used here: 10 −12 to 1 g/m 2 , 1–10 g/m 2 , 10–100 g/m 2 , and >100 g/m 2 .…”

“…The variation of sampling frequency with respect to local time is investigated for two regions of interest: TWP region (330°E to 350°E in longitude and 12°N to 12°S in latitude), and TWA (82°E to 117°E in longitude and 10°N to 30°N in latitude). These two regions were selected due to the high presence of high‐altitude clouds (Brogniez & Kirstetter, 2020; Hartmann & Berry, 2017). In addition, the TWA has a significant impact on the weather and climate of the United States.…”

The C2Omodo Concept: A Tandem of New Generation High Resolution All-Sky Atmospheric Sounders in the Frame of the AOS Mission

“…Two microwave radiometers, the new generation multi-spectral, high-resolution, all-sky atmospheric sounders, SAPHIR NG [2], form the C²OMODO tandem. These instruments inherit from the SAPHIR instrument [2] on-board the French-Indian Megha-Tropiques mission [3] and benefit from technological improvements since the design of SAPHIR, which data is successfully used more than ten years after its launch [4][5] [6][7] [10]. The C²OMODO concept is currently part of the NASA AOS (Atmosphere Observing System) mission, which addresses the following objectives: low and high clouds, convective storms, cold clouds and precipitation, air quality and aerosol attribution, aerosol redistribution and processing, and aerosols direct and indirect effects.…”