A microphysics guide to cirrus – Part 2: Climatologies of clouds and humidity from observations

Abstract

Abstract. This study presents airborne in situ and satellite remote sensing climatologies of cirrus clouds and humidity. The climatologies serve as a guide to the properties of cirrus clouds, with the new in situ database providing detailed insights into boreal midlatitudes and the tropics, while the satellite-borne data set offers a global overview. To this end, an extensive, quality-checked data archive, the Cirrus Guide II in situ database, is created from airborne in situ measurements during 150 flights in 24 campaigns. The archive contains meteorological parameters, ice water content (IWC), ice crystal number concentration (Nice), ice crystal mean mass radius (Rice), relative humidity with respect to ice (RHice), and water vapor mixing ratio (H2O) for each of the flights. Depending on the parameter, the database has been extended by about a factor of 5–10 compared to earlier studies. As one result of our investigation, we show that the medians of Nice, Rice, and RHice have distinct patterns in the IWC–T parameter space. Lookup tables of these variables as functions of IWC and T can be used to improve global model cirrus representation and remote sensing retrieval methods. Another outcome of our investigation is that across all latitudes, the thicker liquid-origin cirrus predominate at lower altitudes, while at higher altitudes the thinner in situ-origin cirrus prevail. Further, examination of the radiative characteristics of in situ-origin and liquid-origin cirrus shows that the in situ-origin cirrus only slightly warm the atmosphere, while liquid-origin cirrus have a strong cooling effect. An important step in completing the Cirrus Guide II is the provision of the global cirrus Nice climatology, derived by means of the retrieval algorithm DARDAR-Nice from 10 years of cirrus remote sensing observations from satellite. The in situ measurement database has been used to evaluate and improve the satellite observations. We found that the global median Nice from satellite observations is almost 2 times higher than the in situ median and increases slightly with decreasing temperature. Nice medians of the most frequently occurring cirrus sorted by geographical regions are highest in the tropics, followed by austral and boreal midlatitudes, Antarctica, and the Arctic. Since the satellite climatologies enclose the entire spatial and temporal Nice occurrence, we could deduce that half of the cirrus are located in the lowest, warmest (224–242 K) cirrus layer and contain a significant amount of liquid-origin cirrus. A specific highlight of the study is the in situ observations of cirrus and humidity in the Asian monsoon anticyclone and the comparison to the surrounding tropics. In the convectively very active Asian monsoon, peak values of Nice and IWC of 30 cm−3 and 1000 ppmv are detected around the cold point tropopause (CPT). Above the CPT, ice particles that are convectively injected can locally add a significant amount of water available for exchange with the stratosphere. We found IWCs of up to 8 ppmv in the Asian monsoon in comparison to only 2 ppmv in the surrounding tropics. Also, the highest RHice values (120 %–150 %) inside of clouds and in clear sky are observed around and above the CPT. We attribute this to the high H2O mixing ratios (typically 3–5 ppmv) observed in the Asian monsoon compared to 1.5 to 3 ppmv found in the tropics. Above the CPT, supersaturations of 10 %–20 % are observed in regions of weak convective activity and up to about 50 % in the Asian monsoon. This implies that the water available for transport into the stratosphere might be higher than the expected saturation value.

Unprecedented Observations of a Nascent In Situ Cirrus in the Tropical Tropopause Layer

“…Heterogeneity of microphysical properties encountered inside cirrus clouds can be explained by small-scale GWs (Jensen et al, 2013). The climatology from Krämer et al (2020) shows (in their Figure 8) that ice concentrations (for radius above 3 µm) in young cirrus are most frequently around 100 L −1 . Although cirrus with ice concentrations above 10,000 L −1 have already been observed (Krämer et al, 2009;Jensen et al, 2009;Krämer et al, 2020), only less than 10% of the observed TTL ice concentrations exceed 1,000 L −1 (Krämer et al, 2020).…”

“…However, Jensen et al (2016a) argued that the overall impact of the high-frequency waves is to increase ice concentrations produced by homogeneous freezing; the quenching of ice nucleation would only represent 11% of the events. In some infrequent cases, TTL cirrus have been observed with ice concentrations above several thousands per liter (Jensen et al, 2013;Krämer et al, 2020), in which case homogeneous nucleation is the only plausible explanation.…”

Cirrus cloud shape detection by tomographic extinction retrievals from infrared limb emission sounder measurements

“…This allows for the measurement of air masses at an angle between 45 • and ≈ 132 • with respect to the flight direction. By constantly panning the instrument over the available angles, the same air masses are measured from multiple directions, which enables the tomographic reconstruction of three-dimensional structures (Ungermann et al, 2011;Krisch et al, 2017Krisch et al, , 2018. In addition to the IR instrument, there is also a standard camera with three channels (red/green/blue) operating in the visible range that observes a much wider field of view.…”

“…The horizontal resolution is on the order of 30 km in the flight-track direction and 70 km orthogonal to that. Circular flight patterns, or, better, a backwards-viewing limb satellite, could further improve the horizontal resolution (Ungermann et al, 2011;Krisch et al, 2017).…”

Properties of ice cloud over Beijing from surface Ka-band radar observations during 2014–2017

“…Dolinar et al (2019) reported that single-layer ice clouds have a global occurrence frequency of about 18 %. Ice clouds are an important component of the planetary radiation budget in terms of magnitude; plus, they influence hydrological and climate sensitivities and affect surface climate (Runheng and Liou, 1985;Yang et al, 2015;Gultepe and Heymsfield, 2016;Lawson et al, 2019).…”